Lithe

<h2 id="overview">Overview</h2>
<p>The standard <a href="/facts/Class-based_programming/n3wudt1B">class-based programming</a> model does not specify a mechanism by which to manipulate objects: where <a href="/facts/Smalltalk/Ru2UPVDE">Smalltalk</a> uses message passing, Lithe uses <a href="/facts/Syntax-directed_translation/QX5kllfS">syntax-directed translation</a> (SDT). SDT is a method of translating a string into a sequence of <i>actions</i> by attaching one such action to each rule of a grammar. Thus, parsing a string of the grammar produces a sequence of rule applications. Lithe merges SDT with the class model by using classes as the non-terminal alphabet of the grammar. Since the grammar class used by Lithe properly contains all context-free grammars, a wide variety of syntax can be described, and SDT provides a simple way to attach semantics to any such syntax.
</p><p>The <i>package</i> is the unit of <a href="/facts/Modularity_(programming)/sNoqKvRD">program modularity</a> in Lithe. A package is divided into two parts: one that defines classes and another that defines rules. <a href="/facts/Information_hiding/dnSDPMaz">Information hiding</a> is achieved by requiring both <i>export</i> keywords on those rules and classes that are to be seen outside a package <i>and</i> that the source package names be included in the <i>with</i> clause of the consumer package.
</p>
<h2 id="examples">Examples</h2>
<p>Programming in Lithe consists of defining rule-action pairs and classes. Take the task of computing the <a href="/facts/Absolute_value/dwJBpEs5">absolute value</a> of a number, for example:
</p>
rule "|" <i:int> "|" return int;
  {if i<0 then return -i else return i end}

<p>After this rule-action pair has been defined, it can be freely used within Lithe source code, for example, the following expression will thereafter be valid:
</p>
|x - y| + 3

<p>The equivalent rule in <a href="/facts/Backus%E2%80%93Naur_form/xbMXDntc">BNF</a> would be:
</p>
<int>  ::=  "|" <int> "|"

<p>Note that the Lithe description swaps the left and right sides of the BNF one, then adds a name to each nonterminal in the BNF right-hand side. These names are used in the action part, which is expressed as a string that is translated into a sequence of actions by using other, previously defined, rule-action pairs (eventually, some of those rule-action pairs will invoke primitive actions). 
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<h2 id="external-links">External links</h2>
<ul><li><a href="http://portal.acm.org/citation.cfm?id=582169">"Lithe: a language combining a flexible syntax and classes"</a></li></ul>

Lithe open-in-new

Lithe