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diff --git a/docs/spec/evaluate.html b/docs/spec/evaluate.html index 892aa7a5..9e221c53 100644 --- a/docs/spec/evaluate.html +++ b/docs/spec/evaluate.html @@ -7,6 +7,7 @@ <h1 id="specification-bqn-evaluation">Specification: BQN evaluation</h1> <p>This page describes the semantics of the code constructs whose grammar is given in <a href="grammar.html">grammar.md</a>. The formation rules there are not named, and here they are identified by either the name of the term or by copying the rule entirely if there are several alternative productions.</p> <p>Here we assume that the referent of each identifier, or equivalently the connections between identifiers, have been identified according to the <a href="scope.html">scoping rules</a>.</p> +<p>Errors described in this page are "evaluation errors" and can be caught by the Catch (<code><span class='Modifier2'>⎊</span></code>) modifier. If an error is caught, evaluation halts without attempting to complete any in-progress node, and is restarted as part of the execution of Catch.</p> <h3 id="programs-and-blocks">Programs and blocks</h3> <p>The result of parsing a valid BQN program is a <code><span class='Function'>PROGRAM</span></code>, and the program is run by evaluating this term.</p> <p>A <code><span class='Function'>PROGRAM</span></code> or <code><span class='Function'>BODY</span></code> is a list of <code><span class='Function'>STMT</span></code>s, which are evaluated in program order. A result is always required for <code><span class='Function'>BODY</span></code> nodes, and sometimes for <code><span class='Function'>PROGRAM</span></code> nodes (for example, when loaded with <code><span class='Function'>•Import</span></code>). If any identifiers in the node's scope are exported, or any of its statements is an <code><span class='Function'>EXPORT</span></code>, then the result is the namespace created in order to evaluate the node. If a result is required but the namespace case doesn't apply, then the last <code><span class='Function'>STMT</span></code> node must be an <code><span class='Function'>EXPR</span></code> and its result is used. The statement <code><span class='Function'>EXPR</span></code> evaluates some APL code and possibly assigns the results, while <code><span class='Value'>nothing</span></code> evaluates any <code><span class='Value'>subject</span></code> or <code><span class='Function'>Derv</span></code> terms it contains but discards the results. An <code><span class='Function'>EXPORT</span></code> statement performs no action.</p> |