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Sinclair BASIC
Dialect of the programming language BASIC

Sinclair BASIC is a dialect of the programming language BASIC used in the 8-bit home computers from Sinclair Research, Timex Sinclair and Amstrad. The Sinclair BASIC interpreter was written by Nine Tiles Networks Ltd.

Designed to run in only 1 KB of RAM, the system makes a number of decisions to lower memory usage. This led to one of Sinclair BASIC's most notable features, that the keywords were entered using single keystrokes; each of the possible keywords was mapped to a key on the keyboard, when pressed, the token would be placed into memory while the entire keyword was printed out on-screen. This made code entry easier whilst simplifying the parser.

The original ZX80 version supported only integer mathematics, which partially made up for some of the memory-saving design notes which had negative impact on performance. When the system was ported to the ZX81 in 1981, a full floating point implementation was added. This version was very slow, among the slowest BASICs on the market at the time, but given the limited capabilities of the machine, this was not a serious concern. The low speed was not mainly due to an inefficient interpreter though, it was an effect of the fact that 70-80% of the machine cycles were consumed by the video hardware. So the Z80 in the ZX81 clocked at 3.25 MHz was "in effect" running at well below 1 MHz from the perspective of the BASIC system.

Performance became a more serious issue with the release of the ZX Spectrum in 1983, which ran too slowly to make full use of the machine's new features. This led to an entirely new BASIC for the following Sinclair QL, as well as a number of 3rd-party BASICs for the Spectrum and its various clones. The original version continued to be modified and ported in the post-Sinclair era.

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History

Clive Sinclair initially met with John Grant, the owner of Nine Tiles, in April 1979 to discuss a BASIC for Sinclair's new computer concept.2 Sinclair was inspired to make a new machine after watching his son enjoy their TRS-80, but that machine's £500 price tag appeared to be a serious limit on its popularity. He wanted a new kit that would expand on their previous MK14 and feature a built-in BASIC at the target price of £79.95. To meet this price point, the machine would ship with only 1 KB of RAM and 4 KB of ROM. Grant suggested using the Forth language instead, but the budget precluded this. Grant wrote the BASIC interpreter between June and July 1979, but the code initially came in at 5 KB and he spent the next month trimming it down. It was initially an incomplete implementation of the 1978 American National Standards Institute (ANSI) Minimal BASIC standard with integer arithmetic only, termed 4K BASIC.3

Even before the ZX80 was introduced in February 1980, the constant downward price-pressure in the industry was allowing the already inexpensive design to be further reduced in complexity and cost. In particular, many of the separate circuits in the ZX80 were re-implemented in a single uncommitted logic array from Ferranti, which allowed the price to be reduced to only £49.95 while increasing the size of the ROM to 8 KB. This work was assigned to Steve Vickers, who joined Nine Tiles in January 1980. Whilst Grant worked on the code interfacing with hardware, Vickers used the larger space to introduce floating-point arithmetic and a suite of trig functions, which were expected of any BASIC from that era, producing 8K BASIC.4 The initial version did not support the ZX Printer and had a bug in its square root function. Nine Tiles provided a new version to address these, but Sinclair was slow to include the new version in the ROMs. The new ROMs were eventually offered to owners of the earlier ZX80 as well.5

When Sinclair lost the contest to build the BBC Computer, he moved ahead with plans to produce a low-cost colour-capable machine that emerged as the ZX Spectrum of April 1982. ROM space would once again be increased, this time to 16 KB. In keeping with his philosophy of making systems for the lowest possible expenditure, Sinclair wanted the absolute minimum changes to the existing 8K BASIC. Although Nine Tiles felt that something much better would be needed for the new machine, the schedule would not allow it, and yet another expansion of the original code was produced. Due to the RAM also being increased, to 48 KB, this version was known as 48K BASIC and eventually 48 BASIC with the introduction of the ZX Spectrum 128 at which time the 16 KB Spectrum was no longer sold and most existing ones in use had been upgraded to 48 KB.67 The new version was available near the end of 1981, but it was "depressingly slow" and "snail like". Additionally, as no prototypes were available until the end of the year, it lacked support for the new line of peripherals Sinclair was planning.8

In February 1982, Nine Tiles began to have disagreements with Sinclair over owed royalties for the various manuals that Nine Tiles had produced. Around the same time, Vickers and his Sinclair counterpart, Richard Altwasser, left their respective companies to start the Jupiter Ace project.9 When the Spectrum was launched the ROM was still not complete, and although Nine Tiles continued working on it until April 1982, by that point 75,000 Spectrums had already been sold and the project was cancelled. The missing functionality was later added by additional code in the ZX Interface 1. After Nine Tiles and Sinclair went their own ways, several new versions of 48 BASIC were created.

In 1983, as part of introducing the Spectrum to the US market as the TS2068, Timex modified it as T/S 2000 BASIC. The new version was incapable of running many Spectrum programs due to the memory location of machine's functions moving. A similar, but somewhat more compatible version, was introduced as part of the Spanish Spectrum 128 of 1985, 128 BASIC.10

Amstrad purchased Sinclair Research in 1986. As Sinclair had never owned the copyright to the language, Amstrad had to arrange a new license with Nine Tiles. Several other versions also appeared in this period as various extensions and clones of the Spectrum were introduced. These included +3 BASIC, BASIC64 and Timex Extended Basic.1112

As of 2015, interpreters exist for modern operating systems,13 and older systems,14 that allow Sinclair Basic to be used easily.

Description

Program editing

Like most home-computer BASICs, Sinclair BASIC is anchored around its line editor. When the machine is booted, it runs BASIC and displays an inverse video "K" at the bottom of the screen to indicate the entry point. When a line is entered and the NEW LINE key is pressed, it either runs immediately if it does not have a line number prefix, or clears the screen and performs the equivalent of a LIST command, placing a ">" cursor after the line number in the most recently entered line.

In contrast to most machines of the era, the editor does not allow freeform editing at any point on the screen. Instead, when the user presses EDIT, the current line of code is copied back to the bottom of the screen. The user can move horizontally through this line using the cursor keys and commits their changes by pressing NEW LINE again. In contrast, on machines like the Commodore 64 or Atari 8-bit computers, the up and down keys can be used to move among the lines in the program and edit them in-place.

The most notable feature of the editor is that keywords are entered using single keystrokes. For instance, on the ZX81, the P key on the keyboard would cause the entire keyword PRINT to be entered into the currently editing line. Once a keyword has been entered, the cursor changes to an "L" to indicate what follows will be interpreted as normal text. For instance, pressing P again at this point would enter a single letter "P".

Keys generally had two separate keywords assigned to them – one above it and one below. Pressing the key in "K" mode would enter the keyword above the key, like PRINT for P. If the system was in "L" mode, one could return to "K" by pressing the shift key – the systems did not initially support lowercase text, so the shift was not otherwise needed. The keywords below the keys required a second keystroke, ⇧ Shift+NEW LINE, which put the editor into "function mode", changing the cursor to an "F". Entering common code often resulted in a significant number of keystrokes.

The system has the advantage of representing all multi-character keywords as a single character in memory, which was a significant savings in the early machines that shipped with only 1 KB of RAM. This single-character representation included multi-character items like <>. This has the added advantages of simplifying the runtime, as it can immediately determine whether a character in the source code is a keyword or text, and also means that keywords are never entered directly, meaning that one can, for instance, have a variable named "PRINT", as the system can determine that it is not the same as the keyword.

As the systems evolved and added new keywords, the entry system became increasingly difficult to use. 48 BASIC in the Spectrum required every key to host up to four keywords. Entering keywords was a time-consuming process of looking over the relatively small type on the keyboard for the appropriate key, and then correctly entering the multiple keystrokes needed to enter it properly. For instance, entering BEEP required one to type CAPS SHIFT+SYMBOL SHIFT to access extended mode (later models include a separate EXTENDED MODE key), keeping SYMBOL SHIFT held down, and then and pressing Z. To improve the complex entry on the Spectrum, the keywords were colour-coded to indicate the required mode:15

  • White: key only
  • Red on the key itself: SYMBOL SHIFT plus the key
  • Green above the key: EXTENDED MODE followed by the key
  • Red below the key: EXTENDED MODE followed by SYMBOL SHIFT plus the key

This concept had run its course, and later machines running 128 BASIC (ZX Spectrum 128, +2, +3, +2A, and +2B) featured a more traditional editor where the user typed-in the keyword as individual characters, similar to other home computers of the era. This required a new tokenizer to convert the line into a similar internal format.

The resulting in-memory storage of the program was otherwise similar to Microsoft BASIC, in that only the keywords are presented as tokens, while non-keywords – like string and numeric constants and variable names – are left in their original typed-in format. However, that typed-in format was not ASCII, but an internal character code that contains both printable characters and the keyword tokens. Although portions of the table, the capital letters A to Z, for instance, are in the same order as in ASCII, their characters correspond to different numeric values, i.e. their code points' offset from zero is different from ASCII's offset of 65. Other characters, like punctuation, may have been moved about even more. The ZX Spectrum character set is the most prominent example of such a character code. Related computers running Sinclair BASIC used similar variants, e.g. the ZX80 or ZX81 character sets. All of these different but related character sets included Sinclair BASIC tokens.

Data types

One uncommon feature of Sinclair BASIC is the way it stores variables in memory. Typically, interpreters use a fixed-size entry to hold data, making it easy to scan the variable table. Due to the extremely limited memory of the ZX series, any wasted space had to be avoided, and this led to the use of a variable-length format. The data types included numbers stored in a 5-byte values, strings with a length and then the characters, and arrays of both of those types. The data was stored in the table itself, which contrasts with most BASICs of the era, where strings and array entries were stored in a separate heap.

The first byte for a variable entry always held the type in the first three bits, and the first character of the name in the next five bits. As was the case in most microcomputer dialects, A, A$, A() and A$() were all different variables and could store different values. Most variables could only have a single-character name; the exception are numeric variables (not arrays), where an alternate format held the first character of the name in those same five bits, but was then followed by additional characters ending with one with its high-bit set. Long variable names were whitespace-independent, and case-insensitive in later versions, so LET Number Of Apples = 5 is the same as LET numberofapples = 5 referred to the same variable.

The downside to this approach is that scanning the table to look up the value of a variable reference is more complex. In addition to testing whether the name matches using the subset of the first byte, if the entry is not the one that is being looked for, the type has to be read from the upper three bits and then the next location of a variable in storage calculated using the type. For instance, if the program encounters the variable "A" and the table starts with the entry for "B$", it fails to match A with B, then reads the type to see it is a string, and then has to read the following length byte and skip forward by that amount of bytes to find the next entry in the table. To make this somewhat easier, arrays also stored a two-byte length, so the entire structure could be skipped over more easily.

A unique feature was the "short float", or integer type. Any numeric variable could store either type, the storage itself did not change and used 5 bytes in either case. Integers were indicated by setting the exponent byte to zero, while floating-point values were stored with an excess-128 format exponent. This meant that it could not store zero as a float and lost one possible exponent magnitude. It also did not use any less memory, as the values were still 5-byte in memory. The advantage to this format is performance; the math library included tests to look for the zero exponent, and if it was seen, it would not attempt to perform various operations on the remaining 3 bytes under certain conditions.

Keyword details

The ZX81 8K BASIC used the shorter forms GOTO, GOSUB, CONT and RAND, whereas the Spectrum 48 BASIC used the longer forms GO TO, GO SUB, CONTINUE and RANDOMIZE. The ZX80 4K BASIC also used these longer forms but differed by using the spelling RANDOMISE. The ZX81 8K BASIC was the only version to use FAST, SCROLL, SLOW and UNPLOT. The ZX80 4K BASIC had the exclusive function TL$(); it was equivalent to the string operator (2 TO ) in later versions.

Unique code points are assigned in the ZX80 character set, ZX81 character set and ZX Spectrum character set for each keyword or multi-character operator, i.e. <=, >=, <>, "" (tokenized on the ZX81 only), ** (replaced with ↑ on the Spectrum). These are expanded by referencing a token table in ROM. Thus, a keyword uses one byte of memory only, a significant saving over traditional letter-by-letter storage. This also meant that the BASIC interpreter could quickly determine any command or function by evaluating one byte, and that the keywords need not be reserved words like in other BASIC dialects or other programming languages, e.g., it is allowed to define a variable named PRINT and output its value with PRINT PRINT. This is also related to the syntax requirement that every line start with a command keyword, and pressing the one keypress for that command at the start of a line changes the editor from command mode to letter mode. Thus, variable assignment requires LET (i.e., LET a=1 not only a=1). This practice is also different from other BASIC dialects. Further, it meant that unlike other BASIC dialects, the interpreter needed no parentheses to identify functions; SIN x was sufficient, no SIN(x) needed (though the latter was allowed). The 4K BASIC ROM of the ZX80 had a short list of exceptions to this: the functions CHR$(), STR$(), TL$(), PEEK(), CODE(), RND(), USR() and ABS() did not have one-byte tokens but were typed in letter-by-letter and required the parentheses. They were listed as the INTEGRAL FUNCTIONS on a label above and to the right of the keyboard.16

128 BASIC, present on ZX Spectrum 128, +2, +3, +2A, and +2B, stored keywords internally in one-byte code points, but used a conventional letter-by-letter BASIC input system. It also introduced two new commands:

  • PLAY, which operated the 128k models' General Instrument AY-3-8910 music chip
  • SPECTRUM, which switched the 128k Spectrum into a 48k Spectrum compatibility mode

The original Spanish ZX Spectrum 128 included four additional BASIC editor commands in Spanish,1718 one of which was undocumented:

  • EDITAR (to edit a line number or invoke the full screen string editor)
  • NUMERO (to renumber the program lines)
  • BORRAR (to delete program lines)
  • ANCHO (to set the column width of the RS-232 device, but undocumented as the code was broken)

Unlike the LEFT$(), MID$() and RIGHT$() functions used in the ubiquitous Microsoft BASIC dialects for home computers, parts of strings in Sinclair BASIC are accessed by numeric range. For example, a$(5 TO 10) gives a substring starting with the 5th and ending with the 10th character of the variable a$. Thus, it is possible to replace the LEFT$() and RIGHT$() commands by simply omitting the left or right array position respectively; for example a$( TO 5) is equivalent to LEFT$(a$,5). Further, a$(5) alone is enough to replace MID$(a$,5,1).

Syntax

Keywords

On the 16K/48K ZX Spectrum (48 BASIC), there are 88 keywords in Sinclair BASIC, denoting commands (of which there are 50), functions and logical operators (31), and other keywords (16, including 9 which are also commands or functions):

KeywordParameters19Entered using20TypeSummary
ABSnumberEXTENDED MODE then GFunctionReturns the absolute value of number21
ACSnumberEXTENDED MODE then SYMBOL SHIFT+WFunctionReturns the arccosine of number22
ANDSYMBOL SHIFT+YLogical operatorReturns true if both conditions on either side of the AND keyword are true, else returns false2324
ASNnumberEXTENDED MODE then SYMBOL SHIFT+QFunctionReturns the arcsine of number25
ATline, column;SYMBOL SHIFT+IOtherUsed in a PRINT statement to print at the line and column specified;26 for example, PRINT AT 5,10;"*" puts a star in column 10 of line 5.
ATNnumberEXTENDED MODE then SYMBOL SHIFT+EFunctionReturns the arctangent of number27
ATTR(line, column)EXTENDED MODE then SYMBOL SHIFT+LFunctionReturns a byte containing information on the colours of the text cell on the screen, corresponding to the specified line and column;note that, unlike most Sinclair BASIC keywords, the parentheses are required; the first three bits indicate the ink (foreground)colour, the fourth, fifth and sixth bits the paper (background) colour, the seventh bit whether the colours are bright or not, and the eight, whether they are flashing28
BEEPduration, pitchEXTENDED MODE then SYMBOL SHIFT+ZCommandProduces sound from the computer's speaker; duration is in seconds, pitch is in semitones above (positive value) or below (negative value) middle C29
BINnumberEXTENDED MODE then BOtherIndicates number is in binary notation30
BORDERnumberBCommandSets the border of the screen to the colour specified by the number3132
BRIGHTnumberEXTENDED MODE then SYMBOL SHIFT+BCommand/otherMakes all following colours brighter if number is 1, or its normal shade if 03334
CATnumberEXTENDED MODE then SYMBOL SHIFT+9CommandDisplays contents of ZX Microdrive specified by number3536
CHR$numberEXTENDED MODE then UFunctionReturns the character corresponding to the decimal number in the computer's character set37
CIRCLEx, y, rEXTENDED MODE then SYMBOL SHIFT+HCommandDraws a circle with its centre at coordinates (x,y) and radius r38
CLEARaddressXCommandClears the screen,39 all variables and the GO SUB stack,40 and optionally sets the maximum RAM address to be used by BASIC41
CLOSE #numberEXTENDED MODE then SYMBOL SHIFT+5CommandCloses the specified stream number for access42
CLSVCommandClears all text and graphics from the screen43
CODEstringEXTENDED MODE then IFunction/otherReturns the number corresponding to the first character in string in the computer's character set;44 also used to save arbitrary chunks memory to tape, disk, etc. and load them back in — see LOAD, SAVE and VERIFY for details
CONTINUECCommandRestarts a program after it has stopped due to an error or the user pressing the CAPS SHIFT+SPACE or BREAK keys45
COPYZCommandSends the currently displayed screen to the printer46
COSnumberEXTENDED MODE then WFunctionReturns the cosine of number47
DATAcomma-separated valuesEXTENDED MODE then DCommand/otherProvides numbers and/or strings to use with the READ command48 and allows saving the contents of an array to tape when used with the SAVE command49 (as SAVE filename DATA array name())
DEF FNname(variable) = operationEXTENDED MODE then 1CommandDefines a custom function that can be used with the FN command;function definitions must be of the form f(x)=operations, for example f(x)=x*2 and the function name may not consist of more than one letter, plus a $-symbol if the function returns a string50
DIMvariable(dimensions)DCommandDeclares an array with the specified dimensions, which may be multi-dimensional (for example, DIM a(10,10); if used with strings, the last dimension indicates the length of each of the strings (thus, DIM a$(2,5) is an array of two strings each of five characters long, and DIM b$(5) is one string of five characters)51
DRAWx, y [, r]WCommandDraws a line in the current INK colour to coordinates (x,y) from the coordinates used by the previous PLOT or DRAW command; if the optional r is supplied, it indicates the radius of the circle segment to be drawn, in radians52
ERASEdrive;"filename"EXTENDED MODE then SYMBOL SHIFT+7CommandDeletes the specified file from a ZX Microdrive5354
EXPnumberEXTENDED MODE then XFunctionReturns e to the power number55
FLASHnumberEXTENDED MODE then SYMBOL SHIFT+VCommand/otherMakes all following text alternate its foreground (INK) and background (PAPER) colours56
FNfunction(value)EXTENDED MODE then SYMBOL SHIFT+2FunctionCalls the function defined earlier in the program using DEF FN57
FORMATdrive;"name"EXTENDED MODE then SYMBOL SHIFT+0CommandFormats the cartridge in the indicated Microdrive and assigns it the identifier name5859
FORvariable = start TO endFCommandStarts a FOR-NEXT loop;60 the variable name may only be one character long61
GO SUBnumberHCommandMakes the program jump to the BASIC line specified by number; when the program encounters the command RETURN, it will jump back to the statement after the GO SUB62
GO TOnumberGCommandMakes the program jump to the BASIC line specified by number
IF condition THENUCommandEvaluates the condition, and if true, executes the statement that follows the keyword THEN that must come after the condition,63 for example IF a=1 THEN LET b=264
INaddressEXTENDED MODE then SYMBOL SHIFT+IFunctionReturns a byte read from the hardware input/output port corresponding to the address65
INKnumberEXTENDED MODE then SYMBOL SHIFT+XCommand/otherSets the foreground colour for text and graphics666768
INKEY$EXTENDED MODE then SYMBOL SHIFT+ZFunctionReturns a string representing the key being pressed on the keyboard at the moment the function is called, or an empty string if none is,69 but does not wait for a keypress
INPUT[prompt,] variableICommandHalts program execution until the user types in something on the keyboard and presses the Enter key, then stores the entered value in the specified variable; if the optional prompt is supplied, this will be shown on the screen70
INTnumberEXTENDED MODE then RFunctionReturns the integer value of number, rounding down to the nearest whole number71 (thus, INT -1.1 returns −2, not −1)
INVERSEnumberEXTENDED MODE then SYMBOL SHIFT+MCommand/otherReverses the colours on all following text if number is 1, so that it uses the current ink colour for the background and the current paper colour for the text, or sets them back to normal if number is 07273
LENstringEXTENDED MODE then KFunctionReturns the number of characters (bytes) in string74
LETvariable=valueLCommandAssigns value to the named variable75
LINEEXTENDED MODE then SYMBOL SHIFT+3Other
  • When used in an INPUT statement before a string variable, will not put quotation marks ("") around its prompt,76 for example INPUT "Name: "; LINE n$
  • When used in a SAVE statement so that when the BASIC program being saved is loaded again, it starts automatically at the line number indicated77
LIST[number]KCommandOutputs the current BASIC program to the screen; if the optional number is provided, it omits all lines with a lower number78
LLIST[number]EXTENDED MODE then SYMBOL SHIFT+VCommandAs LIST except the listing is output to the printer79
LNnumberEXTENDED MODE then SYMBOL SHIFT+ZFunctionReturns the natural logarithm of number80
LOAD"[filename]" [CODE [address[, length]]| DATA variable()]JCommandLoads a program or data into RAM from tape, ZX Microdrive, disk, etc., deleting any existing BASIC program and variables;81 if an empty string ("") is provided, this loads the first program found, else it will search the tape for the program named in the string; if the optional CODE is provided, will load the program into memory at the address it had when it was saved, or at the specified address (length is intended as a safety, to try and load the right program in case there are multiple on the tape with the right name but of different lengths);82 if the optional DATA variable() is provided, will load the data from the tape into the array named variable()83
LPRINTtextEXTENDED MODE then SYMBOL SHIFT+CCommandAs PRINT except output is sent to the printer84
MERGE"[filename]"EXTENDED MODE then SYMBOL SHIFT+TCommandAs LOAD, except it does not delete the current program and variables; if a line number exists in both, that of the newly loaded program overwrites the existing one. Using MERGE prevents a program saved using LINE from auto-running once loaded85
MOVEstream1 TO stream2EXTENDED MODE then SYMBOL SHIFT+6CommandMoves data from one stream (keyboard, screen, file, printer, network, etc.) to another8687
NEWACommandErases the current BASIC program and all variables88
NEXTvariableNCommandCloses a FOR-NEXT loop; the variable must match that of the corresponding FOR command89 — "empty" NEXTs to refer to the immediately preceding FOR in the program are not allowed
NOTconditionSYMBOL SHIFT+SLogical operatorReturns true if the condition is false, else returns false9091
OPEN #streamEXTENDED MODE then SYMBOL SHIFT+4CommandOpens a stream for reading from and/or writing to9293
ORSYMBOL SHIFT+YLogical operatorReturns true if either of the conditions on either side of the OR keyword are true, else returns false9495
OUTaddress, valueEXTENDED MODE then SYMBOL SHIFT+OCommandSends the value (a byte) to the hardware [Memory-mapped I/O|input/output port] corresponding to the address96
OVERnumberEXTENDED MODE then SYMBOL SHIFT+NCommand/otherWill make following text overprint with an XOR operation what is already on the screen if number is 1, instead of erasing it, or erase it if number is 09798
PAPERnumberEXTENDED MODE then SYMBOL SHIFT+CCommand/otherSets the background colour for text and graphics99100101
PAUSEdelayMCommandHalts program execution for the specified delay, in 1 50 {\displaystyle {\tfrac {1}{50}}} of a second in Europe or 1 60 {\displaystyle {\tfrac {1}{60}}} in North America102 (thus, PAUSE 50 halts for one second in Europe)
PEEKaddressEXTENDED MODE then OFunctionReturns a byte representing the contents of the memory location pointed to by address103
PIEXTENDED MODE then MFunctionReturns the value of pi104
PLOTx, yQCommandDraws a pixel in the current INK colour on the screen at the coordinates (x,y)105
POINT(x,y)EXTENDED MODE then SYMBOL SHIFT+8FunctionReturns 1 if the pixel pointed at graphical coordinates (x,y) is currently in the ink (foreground) colour, else returns 0106
POKEaddress, valueOCommandSets the contents of address in RAM to value107
PRINT[AT x,y;] textPCommandPrints text (which must be one or more strings or numbers separated with semicolons) to the screen.108 If used with #0 or #1, it prints in the bottom two (input) lines of the screen; if used with AT, it prints at the specified text coordinates; otherwise, it prints either immediately following the output of any previous PRINT statement (if the previous statement ended in a semicolon), or in the first column of the line below the previous PRINT output,109 defaulting to 0,0.
RANDOMIZE[number]TCommandInitializes the random number generator; if used without a number (or with 0), it does this based on the computer's internal clock, else it uses the number supplied, which must be in the range [1,65535]110
READvariableEXTENDED MODE then ACommandTakes a value from a DATA statement and stores it in the named variable: the first time READ is used, it gets the first value after the first DATA, the second time it gets the next one, and so on111
REMtextECommandBegins a comment in the source code, meaning that everything after the REM statement is ignored, until the end of the line112 — note this includes everything after a colon, which normally begins a new segment: 10 REM Nothing to see here : PRINT "Unprintable" will not produce any output, for example
RESTORE[number]EXTENDED MODE then SCommandResets where READ commands look for values in DATA statements: if used without a number, the next READ will use the first DATA in the program, with a number it will use the first DATA on or after the line whose number is indicated113
RETURNYCommandReturns execution to the first statement following the last GO SUB command that was executed114
RNDEXTENDED MODE then TFunctionReturns a pseudo-random number with eight significant figures in the range [0,1)115
RUN[number]RCommandStarts the current BASIC program, from its first line if no number is specified, else from the line with that number (or the first one after, if it does not exist)116
SAVE"filename" [DATA variable() | LINE number]SCommandSaves the current BASIC program to tape or other storage device, with the filename specified; if the optional LINE followed by a line number is used, then the program will start automatically at the indicated line number when it is LOADed back in; with the optional DATA, the command saves the contents of the array named by the variable instead of the current BASIC program117
SCREEN$[(line, column)]EXTENDED MODE then SYMBOL SHIFT+Function/otherAs a function, identifies the character at the specified line and column on the screen.118 Used after the filename in a LOAD or SAVE command, indicates that the contents of the display memory should be loaded or saved; this essentially makes it a shortcut for CODE 16384,6912119 but does not work with VERIFY because the contents of the display memory will be different by the time that command reads back the saved data;120
SGNnumberEXTENDED MODE then FFunctionReturns 1 if number is positive, 0 if it is 0, and −1 if it is negative121
SINnumberEXTENDED MODE then QFunctionReturns the sine of number122
STEPnumberSYMBOL SHIFT+DOtherIndicates the interval used by a FOR statement,123 for example FOR n=2 TO 6 STEP 2 will skip n=3 and n=5 in the loop
STOPSYMBOL SHIFT+ACommandEnds execution of the current program, exiting to the BASIC editor; can also be given when the computer is waiting for input using the INPUT command;124 once the program is stopped, it can be resumed with CONTINUE
SQRnumberEXTENDED MODE then HFunctionReturns the square root of number125
STR$numberEXTENDED MODE then YFunctionConverts a number to string.
TABcolumnEXTENDED MODE then POtherIn a PRINT statement, makes sure that the text to be output begins in the column specified, wrapping to the next line as necessary, but never more than one line126
TANnumberEXTENDED MODE then EFunctionReturns the tangent of number127
THENstatementSYMBOL SHIFT+GOtherFollows the condition in an IF statement to indicate what should happen when the condition evaluates to true128129
TOSYMBOL SHIFT+FOtherIndicates a range from the number to the left of TO to the number of the right of it, inclusive;130 when used with FOR both numbers must be supplied, while if used to slice strings, either may be left off to indicate the start or end of the string
USRstring or addressEXTENDED MODE then LFunctionWhen called with a single-character string, this returns the memory address at which the glyph for the user-defined graphic character corresponding to that character is defined.131 If called with an address, it starts machine code execution at that address (thus making it one of the few Sinclair BASIC functions to have a Side effect) and returns the contents of the Z80’s BC register pair.132
VALstringEXTENDED MODE then JFunctionEvaluates the string as a number and returns the result;133 this can perform calculations: VAL "1+2" returns 3, for example, and also evaluates variables and even other VAL statements: LET a=1: VAL "a+VAL ""2"""134 also returns 3
VAL$stringEXTENDED MODE then SYMBOL SHIFT+JFunctionSimilar to VAL but evaluates the string as a string135
VERIFY"[filename]"EXTENDED MODE then SYMBOL SHIFT+RCommandReads a program or data from tape or other storage, much like LOAD, but instead of loading it into memory, compares it with the program or data that is already in memory. This is intended to be used immediately after a SAVE command, to make sure the program or data has been saved without corruption.136

Official versions

4K BASIC

4K BASIC for ZX80137 (so named for residing in 4 KiB read-only memory (ROM)), was developed by John Grant of Nine Tiles for the ZX80. It has integer-only arithmetic.

  • System Commands: NEW RUN LIST LOAD SAVE
  • Control Statements: GOTO IF THEN GOSUB STOP RETURN FOR TO NEXT CONTINUE
  • Input/Output Statements: PRINT INPUT
  • Assignment Statement: LET
  • Other Statements: CLEAR CLS DIM REM RANDOMIZE POKE
  • Functions: ABS CHR$ CODEPEEK RND STR$ TL$ USR

8K BASIC

8K BASIC is the ZX81 BASIC (also available as an upgrade for the ZX80138), updated with floating-point arithmetic by Steve Vickers, so named for residing in 8 KiB ROM.

  • Statements: PRINT RAND LET CLEAR RUN LIST GOTO CONT INPUT NEW REM PRINT STOP BREAK IF STOP FOR NEXT TO STEP SLOW FAST GOSUB RETURN SAVE LOAD CLS SCROLL PLOT UNPLOT PAUSE LPRINT LLIST COPY DIM POKE NEW
  • Functions: ABS SGN SIN COS TAN ASN ACS ATN LN EXP SQR INT PI RND FUNCTION LEN VALSTR$ NOT CODE CHR$ INKEY$ AT TAB INKEY$ PEEK USR

48 BASIC

48 BASIC is the BASIC for the original 16/48 KB RAM ZX Spectrum (and clones), with colour and more peripherals added by Steve Vickers and John Grant. It resides in 16 KB ROM and began to be called 48 BASIC with the introduction of the ZX Spectrum 128 at which time the 16 KB Spectrum was no longer sold and most existing ones in use had been upgraded to 48 KB.139

128 BASIC

128 BASIC is the BASIC for the ZX Spectrum 128.140 It offers extra commands and uses letter-by-letter input.

  • New commands: LOAD ! SAVE ! MERGE ! ERASE ! PLAY SPECTRUM

+3 BASIC

+3 BASIC is the BASIC with disk support for the ZX Spectrum +3 and +2A.141

  • New commands: FORMAT COPY

T/S 2000 BASIC

T/S 2000 BASIC is used on the Spectrum-compatible Timex Sinclair 2068 (T/S 2068) and adds the following six new keywords:

  • DELETE deletes BASIC program line ranges.
  • FREE is a function that gives the amount of free RAM. PRINT FREE will show how much RAM is free.
  • ON ERR is an error-handling function mostly used as ON ERR GO TO or ON ERR CONT.
  • RESET can be used to reset the behaviour of ON ERR. It was also intended to reset peripherals.
  • SOUND controls the AY-3-8192 sound chip.
  • STICK is a function that gives the position of the internal joystick (Timex Sinclair 2090).

BASIC64

BASIC64 by Timex of Portugal, is a software extension142 to allow better Basic programming with the 512×192 and dual display areas graphic modes available only on Timex Sinclair computers. This extension adds commands and does a complete memory remap to avoid the system overwriting the extended screen memory area. Two versions exist due to different memory maps – a version for TC 2048 and a version for T/S 2068 and TC 2068.

  • PRINT # prints to a specific output channel.
  • LIST # lists the program to a specific output channel.
  • CLS* clears both display areas.
  • INK* sets ink colour for both display areas
  • PAPER* sets paper colour both display areas
  • SCREEN$ selects the high / normal resolution modes.
  • PLOT* plots a pixel and updates the drawing position.
  • LINE draws a line from the previous PLOT position, supporting arc drawing
  • CIRCLE* draws a circle or oval, depending on screen mode.

Timex Extended Basic

Timex Extended Basic by Timex of Portugal is used on the Timex Computer 3256, adding TEC – Timex Extended Commands commands supporting the AY-3-8912 sound chip, RS-232 network and the 512x192 pixel high resolution graphic mode.143144

  • RAM drive commands: LOAD! SAVE! CAT! MERGE! ERASE! CLEAR!
  • RS-232 commands: FORMAT! LPRINT LLIST
  • AY-3-8912 commands: BEEP!
  • 512 x 192 resolution commands: SCREEN$ DRAW! PLOT! CIRCLE!

Other versions, extensions, derivatives and successors

Interpreters for the ZX Spectrum family

Several ZX Spectrum interpreters exist.145

  • Beta BASIC by Dr. Andy Wright, was originally a BASIC extension, but became a full interpreter.146
  • YS MegaBasic by Mike Leaman.147148
  • ZebraOS by Zebra Systems in New York, a cartridge version of T/S 2000 BASIC that used the 512×192 screen mode.149
  • Sea Change ROM by Steve Vickers and Ian Logan, modified by Geoff Wearmouth, a replacement ROM with an enhanced Sinclair BASIC.150
  • Gosh Wonderful by Geoff Wearmouth, a replacement ROM that fixes bugs and adds a tokenizer, stream lister, delete and renumber commands.151152
  • OpenSE BASIC (formerly SE BASIC) by Andrew Owen, a replacement ROM with bug fixes and many enhancements including ULAplus153 support, published as open source in 2011154155156

Compilers for the ZX Spectrum family

Several ZX Spectrum compilers exist.157

  • HiSoft COLT Compiler (a.k.a. HiSoft COLT Integer Compiler)158159
  • HiSoft BASIC (a.k.a. HiSoft BASIC Compiler), an integer and floating-point capable compiler160161
  • Laser Compiler162163
  • Softek 'IS' Integer Compiler164165 (successor to Softek Integer Compiler166)
  • Softek 'FP' Full Compiler167168
  • ZIP Compiler169170

Derivatives and successors for other computers

  • SuperBASIC, a much more advanced BASIC dialect introduced with the Sinclair QL personal computer, with some similarities to the earlier Sinclair BASICs171
  • SAM Basic, the BASIC on the SAM Coupé, generally considered a ZX Spectrum clone172
  • ROMU6 by Cesar and Juan Hernandez – MSX173
  • Spectrum 48 by Whitby Computers – Commodore 64174
  • Sparky eSinclair BASIC by Richard Kelsh, an operating system loosely based on ZX Spectrum BASIC - Zilog eZ80175
  • Sinbas by Pavel Napravnik – DOS176
  • Basic177 (and CheckBasic178) by Philip Kendall - Unix
  • BINSIC179 by Adrian McMenamin, a reimplementation in Groovy closely modelled on ZX81 BASIC – Java
  • BASin180 by Paul Dunn, a complete Sinclair BASIC integrated development environment (IDE) based on a ZX Spectrum emulator181 – Windows
  • SpecBAS182 (a.k.a. SpecOS) by Paul Dunn, an integrated development environment (IDE) providing an enhanced superset of Sinclair BASIC – Windows, Linux, Pandora, and Raspberry Pi
  • ZX-Basic183 Backwardly compatible, but enhanced compiler of Sinclair BASIC programs the ZX Spectrum, written in Python, freely available for Windows, Linux and Mac OS
  • ZX-Basicus184 by Juan-Antonio Fernández-Madrigal, a synthesizer, analyzer, optimizer, interpreter and debugger of Sinclair BASIC 48K for PCs, freely downloadable for Linux and Windows.

See also

Notes

Bibliography

  • Adamson, Ian; Kennedy, Richard (1986). Sinclair and the 'sunrise' Technology. Penguin.
  • Ardley, Neil (1984). Sinclair ZX Spectrum+ User Guide. Dorling Kindersley in association with Sinclair Research. ISBN 0-86318-080-9.
  • Vickers, Steven (1982). Sinclair ZX Spectrum BASIC Programming. Sinclair Research.
  • Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research.
  • Cambridge Communication (1983). Sinclair ZX Spectrum Microdrive and Interface 1 manual. Sinclair Research.

References

  1. Garfield, Simon (28 February 2010). "Sir Clive Sinclair: "I don't use a computer at all"". The Guardian. Retrieved 23 May 2011. He is keen to credit [...], not least Nine Tiles, the company that made the Basic operating software. https://www.theguardian.com/technology/2010/feb/28/clive-sinclair-interview-simon-garfield ↩

  2. Adamson & Kennedy, p. 63. sfn error: no target: CITEREFAdamsonKennedy (help) ↩

  3. Adamson & Kennedy 1986, p. 64. - Adamson, Ian; Kennedy, Richard (1986). Sinclair and the 'sunrise' Technology. Penguin. https://rk.nvg.ntnu.no/sinclair/computers/zx81/zx81_sst.htm ↩

  4. Adamson & Kennedy 1986, p. 70. - Adamson, Ian; Kennedy, Richard (1986). Sinclair and the 'sunrise' Technology. Penguin. https://rk.nvg.ntnu.no/sinclair/computers/zx81/zx81_sst.htm ↩

  5. "ZX80 – 8K BASIC ROM Upgrade". www.fruitcake.plus.com. http://www.fruitcake.plus.com/Sinclair/ZX80/ROMUpgrade/ZX80_ROMUpgrade.htm ↩

  6. "World of Spectrum - Documentation - ZX Spectrum +3 - Chapter 7". worldofspectrum.org. https://worldofspectrum.org/ZXSpectrum128+3Manual/chapter7.html ↩

  7. "World of Spectrum - Documentation - ZX Spectrum 128 Manual Page 6". worldofspectrum.org. https://worldofspectrum.org/ZXSpectrum128Manual/sp128p06.html ↩

  8. Smith, Tony (23 April 2012). "Happy 30th Birthday, Sinclair ZX Spectrum". The Register. https://www.theregister.com/2012/04/23/retro_week_sinclair_zx_spectrum_at_30?page=2 ↩

  9. Adamson & Kennedy 1986, p. 88. - Adamson, Ian; Kennedy, Richard (1986). Sinclair and the 'sunrise' Technology. Penguin. https://rk.nvg.ntnu.no/sinclair/computers/zx81/zx81_sst.htm ↩

  10. "World of Spectrum - Documentation - ZX Spectrum 128 Manual Page 6". worldofspectrum.org. https://worldofspectrum.org/ZXSpectrum128Manual/sp128p06.html ↩

  11. "World of Spectrum - Documentation - ZX Spectrum 128 Manual Page 6". worldofspectrum.org. https://worldofspectrum.org/ZXSpectrum128Manual/sp128p06.html ↩

  12. "World of Spectrum - Documentation - ZX Spectrum +3 - Chapter 7". worldofspectrum.org. https://worldofspectrum.org/ZXSpectrum128+3Manual/chapter7.html ↩

  13. Dunn, Paul (7 December 2022), SpecBAS, retrieved 12 December 2022 https://github.com/ZXDunny/SpecBAS ↩

  14. "CSDb". Commodore 64 Scene Database. Retrieved 12 December 2022. https://csdb.dk/search/?seinsel=releases&search=spectrum+emulator&all=1 ↩

  15. Vickers 1983, p. 7–8. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  16. "Picture of ZX80". https://upload.wikimedia.org/wikipedia/commons/5/54/Sinclair_ZX80_%281980%29_-_Computer_History_Museum.jpg ↩

  17. "Spectrum 128 ROM Disassembly - Spanish Spectrum 128". www.fruitcake.plus.com. http://www.fruitcake.plus.com/Sinclair/Spectrum128/ROMDisassembly/Spectrum128ROMDisassembly3.htm ↩

  18. Sinclair (1985). ZX Spectrum 128 Introducción y Guía de Funcionamiento. Sinclair Research Ltd and Investronica, S. A. p. 9. http://archive.org/details/128_20220808_202208 ↩

  19. Optional parameters are enclosed in [square brackets] ↩

  20. These assume the computer is in  K  (keyword) mode, which it normally is at the start of a line when entering BASIC. On the Spectrum 16K and 48K, Extended Mode is entered by pressing CAPS SHIFT and SYMBOL SHIFT simultaneously rather than the EXTENDED MODE key that is present on the Spectrum+ and later models. ↩

  21. Vickers 1983, p. 59. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  22. Vickers 1983, p. 70. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  23. “False” in Sinclair BASIC equates to 0 (zero), everything else equates to “true”. Functions that return true-or-false values thus actually return 0 for false and 1 for true, while AND usually returns the first of the conditions supplied for true, or 1 if no numerical values were given. For example, 6 AND 7 returns 6, while NOT 6=7 returns 1. ↩

  24. Vickers 1983, p. 85. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  25. Vickers 1983, p. 69–70. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  26. Vickers 1983, p. 101. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  27. Vickers 1983, p. 70. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  28. Vickers 1983, p. 116. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  29. Vickers 1983, p. 135. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  30. Vickers 1983, p. 93. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  31. The available numbers for colours are: 12345670blueredmagentagreencyanyellowwhiteblack In all colour-related commands, the number 8 may be used to indicate “transparent” while in INK and PAPER may also be set to 9 for “contrast” — that is, to put a dark colour on a light background or vice versa automatically. ↩

  32. Vickers 1983, p. 113. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  33. INK, PAPER, FLASH, BRIGHT, OVER and INVERSE set attributes for outputting text and graphics to the screen. They can be used either as commands, to apply to all subsequent output until set again, or within a PRINT statement, to apply only from that point until the end of the statement. ↩

  34. Vickers 1983, p. 110–111. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  35. CAT, ERASE, FORMAT and MOVE were originally designed to be used with peripherals, but at the launch of ZX Spectrum, they had not been completely implemented, such that their use generated an error message (Invalid Stream). Later with the aid of the ZX Interface 1 shadow ROM, they were used for the ZX Microdrive. (The shadow ROM was paged when the BASIC interpreter detected a syntax error, which is why most ZX Microdrive commands use a "*"). /wiki/ZX_Microdrive ↩

  36. Cambridge Communication 1983, p. 15. - Cambridge Communication (1983). Sinclair ZX Spectrum Microdrive and Interface 1 manual. Sinclair Research. ↩

  37. Vickers 1983, p. 91. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  38. Vickers 1983, p. 123. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  39. Vickers 1983, p. 103. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  40. "World of Spectrum - Documentation - ZX Spectrum manual - Chapter 24". worldofspectrum.org. https://worldofspectrum.org/ZXBasicManual/zxmanchap24.html ↩

  41. Vickers 1983, p. 168. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  42. CAT, ERASE, FORMAT and MOVE were originally designed to be used with peripherals, but at the launch of ZX Spectrum, they had not been completely implemented, such that their use generated an error message (Invalid Stream). Later with the aid of the ZX Interface 1 shadow ROM, they were used for the ZX Microdrive. (The shadow ROM was paged when the BASIC interpreter detected a syntax error, which is why most ZX Microdrive commands use a "*"). /wiki/ZX_Microdrive ↩

  43. Vickers 1983, p. 103. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  44. Vickers 1983, p. 91. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  45. Vickers 1983, p. 19. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  46. Vickers 1983, p. 151. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  47. Vickers 1983, p. 68. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  48. Vickers 1983, p. 41. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  49. Vickers 1983, p. 142. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  50. Vickers 1983, p. 60. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  51. Vickers 1983, p. 79–81. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  52. Vickers 1983, p. 11–123. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  53. CAT, ERASE, FORMAT and MOVE were originally designed to be used with peripherals, but at the launch of ZX Spectrum, they had not been completely implemented, such that their use generated an error message (Invalid Stream). Later with the aid of the ZX Interface 1 shadow ROM, they were used for the ZX Microdrive. (The shadow ROM was paged when the BASIC interpreter detected a syntax error, which is why most ZX Microdrive commands use a "*"). /wiki/ZX_Microdrive ↩

  54. Cambridge Communication 1983, p. 18. - Cambridge Communication (1983). Sinclair ZX Spectrum Microdrive and Interface 1 manual. Sinclair Research. ↩

  55. Vickers 1983, p. 66. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  56. INK, PAPER, FLASH, BRIGHT, OVER and INVERSE set attributes for outputting text and graphics to the screen. They can be used either as commands, to apply to all subsequent output until set again, or within a PRINT statement, to apply only from that point until the end of the statement. ↩

  57. Vickers 1983, p. 60. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  58. CAT, ERASE, FORMAT and MOVE were originally designed to be used with peripherals, but at the launch of ZX Spectrum, they had not been completely implemented, such that their use generated an error message (Invalid Stream). Later with the aid of the ZX Interface 1 shadow ROM, they were used for the ZX Microdrive. (The shadow ROM was paged when the BASIC interpreter detected a syntax error, which is why most ZX Microdrive commands use a "*"). /wiki/ZX_Microdrive ↩

  59. Cambridge Communication 1983, p. 19. - Cambridge Communication (1983). Sinclair ZX Spectrum Microdrive and Interface 1 manual. Sinclair Research. ↩

  60. Vickers 1983, p. 31. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  61. Vickers 1983, p. 32. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  62. Vickers 1983, p. 37. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  63. Vickers 1983, p. 25. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  64. Unlike many other BASIC dialects, Sinclair Basic did not include the ELSE operator in the IF–THEN[–ELSE] clause. A workaround would be to use an IF–THEN–GO TO construct instead, bypassing the lines that would have been in an ELSE clause with the GO TO ↩

  65. Vickers 1983, p. 159. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  66. The available numbers for colours are: 12345670blueredmagentagreencyanyellowwhiteblack In all colour-related commands, the number 8 may be used to indicate “transparent” while in INK and PAPER may also be set to 9 for “contrast” — that is, to put a dark colour on a light background or vice versa automatically. ↩

  67. INK, PAPER, FLASH, BRIGHT, OVER and INVERSE set attributes for outputting text and graphics to the screen. They can be used either as commands, to apply to all subsequent output until set again, or within a PRINT statement, to apply only from that point until the end of the statement. ↩

  68. Vickers 1983, p. 110. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  69. Vickers 1983, p. 131. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  70. Vickers 1983, p. 16. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  71. Vickers 1983, p. 59. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  72. INK, PAPER, FLASH, BRIGHT, OVER and INVERSE set attributes for outputting text and graphics to the screen. They can be used either as commands, to apply to all subsequent output until set again, or within a PRINT statement, to apply only from that point until the end of the statement. ↩

  73. Vickers 1983, p. 112. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  74. Vickers 1983, p. 57. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  75. Vickers 1983, p. 13. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  76. Vickers 1983, p. 101. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  77. Vickers 1983, p. 144. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  78. Vickers 1983, p. 15. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  79. Vickers 1983, p. 151. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  80. Vickers 1983, p. 67. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  81. Vickers 1983, p. 16. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  82. Vickers 1983, p. 142–143. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  83. Vickers 1983, p. 142. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  84. Vickers 1983, p. 151. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  85. Vickers 1983, p. 147. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  86. CAT, ERASE, FORMAT and MOVE were originally designed to be used with peripherals, but at the launch of ZX Spectrum, they had not been completely implemented, such that their use generated an error message (Invalid Stream). Later with the aid of the ZX Interface 1 shadow ROM, they were used for the ZX Microdrive. (The shadow ROM was paged when the BASIC interpreter detected a syntax error, which is why most ZX Microdrive commands use a "*"). /wiki/ZX_Microdrive ↩

  87. Cambridge Communication 1983, p. 39. - Cambridge Communication (1983). Sinclair ZX Spectrum Microdrive and Interface 1 manual. Sinclair Research. ↩

  88. Vickers 1983, p. 16. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  89. Vickers 1983, p. 31–32. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  90. “False” in Sinclair BASIC equates to 0 (zero), everything else equates to “true”. Functions that return true-or-false values thus actually return 0 for false and 1 for true, while AND usually returns the first of the conditions supplied for true, or 1 if no numerical values were given. For example, 6 AND 7 returns 6, while NOT 6=7 returns 1. ↩

  91. Vickers 1983, p. 85. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  92. CAT, ERASE, FORMAT and MOVE were originally designed to be used with peripherals, but at the launch of ZX Spectrum, they had not been completely implemented, such that their use generated an error message (Invalid Stream). Later with the aid of the ZX Interface 1 shadow ROM, they were used for the ZX Microdrive. (The shadow ROM was paged when the BASIC interpreter detected a syntax error, which is why most ZX Microdrive commands use a "*"). /wiki/ZX_Microdrive ↩

  93. Cambridge Communication 1983, p. 22. - Cambridge Communication (1983). Sinclair ZX Spectrum Microdrive and Interface 1 manual. Sinclair Research. ↩

  94. “False” in Sinclair BASIC equates to 0 (zero), everything else equates to “true”. Functions that return true-or-false values thus actually return 0 for false and 1 for true, while AND usually returns the first of the conditions supplied for true, or 1 if no numerical values were given. For example, 6 AND 7 returns 6, while NOT 6=7 returns 1. ↩

  95. Vickers 1983, p. 85. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  96. Vickers 1983, p. 159. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  97. INK, PAPER, FLASH, BRIGHT, OVER and INVERSE set attributes for outputting text and graphics to the screen. They can be used either as commands, to apply to all subsequent output until set again, or within a PRINT statement, to apply only from that point until the end of the statement. ↩

  98. Vickers 1983, p. 112. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  99. The available numbers for colours are: 12345670blueredmagentagreencyanyellowwhiteblack In all colour-related commands, the number 8 may be used to indicate “transparent” while in INK and PAPER may also be set to 9 for “contrast” — that is, to put a dark colour on a light background or vice versa automatically. ↩

  100. INK, PAPER, FLASH, BRIGHT, OVER and INVERSE set attributes for outputting text and graphics to the screen. They can be used either as commands, to apply to all subsequent output until set again, or within a PRINT statement, to apply only from that point until the end of the statement. ↩

  101. Vickers 1983, p. 110. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  102. Vickers 1983, p. 129. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  103. Vickers 1983, p. 130. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  104. Vickers 1983, p. 67. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  105. Vickers 1983, p. 121. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  106. Vickers 1983, p. 123. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  107. Vickers 1983, p. 163. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  108. Vickers 1983, p. 13. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  109. Vickers 1983, p. 101. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  110. Vickers 1983, p. 74. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  111. Vickers 1983, p. 41. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  112. Vickers 1983, p. 16. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  113. Vickers 1983, p. 42. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  114. Vickers 1983, p. 37. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  115. Vickers 1983, p. 73. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  116. Vickers 1983, p. 14. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  117. Vickers 1983, p. 142. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  118. Vickers 1983, p. 101. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  119. The Spectrum’s display memory starts at address 16384 and is 6912 bytes long ↩

  120. Vickers 1983, p. 143. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  121. Vickers 1983, p. 59. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  122. Vickers 1983, p. 68. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  123. Vickers 1983, p. 32. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  124. Vickers 1983, p. 14. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  125. Vickers 1983, p. 60. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  126. Vickers 1983, p. 103. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  127. Vickers 1983, p. 69. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  128. Unlike many other BASIC dialects, Sinclair Basic did not include the ELSE operator in the IF–THEN[–ELSE] clause. A workaround would be to use an IF–THEN–GO TO construct instead, bypassing the lines that would have been in an ELSE clause with the GO TO ↩

  129. Vickers 1983, p. 25. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  130. Vickers 1983, p. 32, 51. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  131. Vickers 1983, p. 93. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  132. Vickers 1983, p. 180. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  133. Vickers 1983. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

  134. A string inside a string must have its quotes doubled in Sinclair BASIC ↩

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  136. Vickers 1983, p. 141. - Vickers, Steven (1983). Sinclair ZX Spectrum BASIC Programming (2 ed.). Sinclair Research. ↩

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