diff options
Diffstat (limited to 'docs/spec/evaluate.html')
| -rw-r--r-- | docs/spec/evaluate.html | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/docs/spec/evaluate.html b/docs/spec/evaluate.html index 3ba25d9e..be087db0 100644 --- a/docs/spec/evaluate.html +++ b/docs/spec/evaluate.html @@ -15,8 +15,9 @@ <p>The only remaining step before evaluating the <code><span class='Function'>BODY</span></code> is to bind the inputs and other names. Special names are always bound when applicable: <code><span class='Value'>๐จ๐ฉ๐ค</span></code> if arguments are used, <code><span class='Value'>๐จ</span></code> if there is a left argument, <code><span class='Value'>๐๐</span></code> if operands are used, and <code><span class='Modifier'>_๐ฃ</span></code> and <code><span class='Modifier2'>_๐ฃ_</span></code> for modifiers and combinators, respectively. Any names in the header are also bound, allowing multiple assignment for arguments.</p> <p>If there is no left argument, but the <code><span class='Function'>BODY</span></code> contains <code><span class='Value'>๐จ</span></code> at the top level, then it is conceptually re-parsed with <code><span class='Value'>๐จ</span></code> replaced by <code><span class='Nothing'>ยท</span></code> to give a monadic version before application; this modifies the syntax tree by replacing some instances of <code><span class='Value'>arg</span></code> with <code><span class='Value'>nothing</span></code>. However, it also causes an error if, in a function that is called with no left argument, <code><span class='Value'>๐จ</span></code> is used as an operand or list element, where <code><span class='Value'>nothing</span></code> is not allowed by the grammar. The same effect can also be achieved dynamically by treating <code><span class='Nothing'>ยท</span></code> as a value and checking for it during execution. If it is used as a left argument, then the function should instead be called with no left argument (and similarly in trains); it it is used as a right argument, then the function and its left argument are evaluated but rather than calling the function <code><span class='Nothing'>ยท</span></code> is "returned" immediately; and if it is used in another context then it causes an error.</p> <h3 id="assignment">Assignment</h3> -<p>An <em>assignment</em> is one of the four rules containing <code><span class='Function'>ASGN</span></code>. It is evaluated by first evaluating the right-hand-side <code><span class='Value'>subExpr</span></code>, <code><span class='Function'>FuncExpr</span></code>, <code><span class='Modifier'>_m1Expr</span></code>, or <code><span class='Modifier2'>_m2Exp_</span></code> expression, and then storing the result in the left-hand-side identifier or identifiers. The result of the assignment expression is the result of its right-hand side. Except for subjects, only a lone identifier is allowed on the left-hand side and storage sets it equal to the result. For subjects, <em>multiple assignment</em> with a list left-hand side is also allowed. Multiple assignment is performed recursively by assigning right-hand-side values to the left-hand-side targets, with single-identifier (<code><span class='Value'>s</span></code>) assignment as the base case. When matching the right-hand side to a list left-hand side, the left hand side is treated as a list of <code><span class='Value'>lhs</span></code> targets. The evaluated right-hand side must be a list (rank-1 array) of the same length, and is matched to these targets element-wise.</p> +<p>An <em>assignment</em> is one of the four rules containing <code><span class='Function'>ASGN</span></code>, other than <code><span class='Function'>IMPORT</span></code>. It is evaluated by first evaluating the right-hand-side <code><span class='Value'>subExpr</span></code>, <code><span class='Function'>FuncExpr</span></code>, <code><span class='Modifier'>_m1Expr</span></code>, or <code><span class='Modifier2'>_m2Exp_</span></code> expression, and then storing the result in the left-hand-side identifier or identifiers. The result of the assignment expression is the result of its right-hand side. Except for subjects, only a lone identifier is allowed on the left-hand side and storage sets it equal to the result. For subjects, <em>multiple assignment</em> with a list left-hand side is also allowed. Multiple assignment is performed recursively by assigning right-hand-side values to the left-hand-side targets, with single-identifier (<code><span class='Value'>s</span></code>) assignment as the base case. When matching the right-hand side to a list left-hand side, the left hand side is treated as a list of <code><span class='Value'>lhs</span></code> targets. The evaluated right-hand side must be a list (rank-1 array) of the same length, and is matched to these targets element-wise.</p> <p><em>Modified assignment</em> is the subject assignment rule <code><span class='Value'>lhs</span> <span class='Function'>Derv</span> <span class='String'>"โฉ"</span> <span class='Value'>subExpr</span></code>. In this case, <code><span class='Value'>lhs</span></code> should be evaluated as if it were a <code><span class='Value'>subExpr</span></code> (the syntax is a subset of <code><span class='Value'>subExpr</span></code>), and the result of the function application <code><span class='Value'>lhs</span> <span class='Function'>Derv</span> <span class='Value'>subExpr</span></code> should be assigned to <code><span class='Value'>lhs</span></code>, and is also the result of the modified assignment expression.</p> +<p>The <code><span class='Function'>IMPORT</span></code> rule resembles a multiple assignment. However, in this case the values passed do not form a list but rather a module or namespace, which in this specification is not a value accessible to the programmer. To evaluate the <code><span class='Function'>IMPORT</span></code> the <code><span class='Value'>brNS</span></code> side is evaluated, then each inner variable mentioned in the <code><span class='Value'>nsLHS</span></code> term is extracted and assigned to the corresponding outer identifier. Typically the two will both share the <code><span class='Function'>LHS_NAME</span></code>, but if <code><span class='Gets'>โ</span></code> is used in an <code><span class='Function'>NS_VAR</span></code> then the <code><span class='Value'>lhs</span></code> term refers to the outer identifier and <code><span class='Function'>LHS_NAME</span></code> to the inner one. Since <code><span class='Function'>IMPORT</span></code> is a statement and not an expression, it doesn't have a result value.</p> <h3 id="expressions">Expressions</h3> <p>We now give rules for evaluating an <code><span class='Value'>atom</span></code>, <code><span class='Function'>Func</span></code>, <code><span class='Modifier'>_mod1</span></code> or <code><span class='Modifier2'>_mod2_</span></code> expression (the possible options for <code><span class='Function'>ANY</span></code>). A literal or primitive <code><span class='Value'>sl</span></code>, <code><span class='Function'>Fl</span></code>, <code><span class='Modifier'>_ml</span></code>, or <code><span class='Modifier2'>_cl_</span></code> has a fixed value defined by the specification (<a href="literal.html">literals</a> and <a href="primitive.html">built-ins</a>). An identifier <code><span class='Value'>s</span></code>, <code><span class='Function'>F</span></code>, <code><span class='Modifier'>_m</span></code>, or <code><span class='Modifier2'>_c_</span></code> is evaluated by returning its value; because of the scoping rules it must have one when evaluated. A parenthesized expression such as <code><span class='String'>"("</span> <span class='Modifier'>_modExpr</span> <span class='String'>")"</span></code> simply returns the result of the interior expression. A braced construct such as <code><span class='Function'>BraceFunc</span></code> is defined by the evaluation of the statements it contains after all parameters are accepted. Finally, a list <code><span class='String'>"โจ"</span> <span class='Separator'>โ</span><span class='Value'>?</span> <span class='Paren'>(</span> <span class='Paren'>(</span> <span class='Function'>EXPR</span> <span class='Separator'>โ</span> <span class='Paren'>)</span><span class='Value'>*</span> <span class='Function'>EXPR</span> <span class='Separator'>โ</span><span class='Value'>?</span> <span class='Paren'>)</span><span class='Value'>?</span> <span class='String'>"โฉ"</span></code> or <code><span class='Function'>ANY</span> <span class='Paren'>(</span> <span class='String'>"โฟ"</span> <span class='Function'>ANY</span> <span class='Paren'>)</span><span class='Function'>+</span></code> consists grammatically of a list of expressions. To evaluate it, each expression is evaluated in source order and their results are placed as elements of a rank-1 array. The two forms have identical semantics but different punctuation.</p> <p>Rules in the table below are function and modifier evaluation.</p> |