From 7de47f9a7db71a179ba3124d39cc2c5be2000fd4 Mon Sep 17 00:00:00 2001 From: Marshall Lochbaum Date: Sat, 16 Apr 2022 17:23:57 -0400 Subject: =?UTF-8?q?Specify=20ordering=20of=20destructuring=20=E2=86=A9=20w?= =?UTF-8?q?ith=20error=20catching?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- docs/spec/evaluate.html | 1 + 1 file changed, 1 insertion(+) (limited to 'docs/spec/evaluate.html') diff --git a/docs/spec/evaluate.html b/docs/spec/evaluate.html index c9c45110..9f00a28d 100644 --- a/docs/spec/evaluate.html +++ b/docs/spec/evaluate.html @@ -20,6 +20,7 @@

Assignment

An assignment is one of the four rules containing ASGN. It is evaluated by first evaluating the right-hand-side subExpr, FuncExpr, _m1Expr, or _m2Exp_ 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, destructuring assignment is performed when an lhs is lhsList or lhsStr. Destructuring assignment is performed recursively by assigning right-hand-side values to the left-hand-side targets, with single-identifier assignment as the base case. The target "·" is also possible in place of a NAME, and performs no assignment.

The right-hand-side value, here called v, in destructuring assignment must be a list (rank 1 array) or namespace. If it's a list, then each LHS_ENTRY node must be an LHS_ELT. The left-hand side is treated as a list of lhs targets, and matched to v element-wise, with an error if the two lists differ in length. If v is a namespace, then the left-hand side must be an lhsStr where every LHS_ATOM is an NAME, or an lhsList where every LHS_ENTRY is an NAME or lhs "⇐" NAME, so that it can be considered a list of NAME nodes some of which are also associated with lhs nodes. To perform the assignment, the value of each name is obtained from the namespace v, giving an error if v does not define that name. The value is assigned to the lhs node if present (which may be a destructuring assignment or simple subject assignment), and otherwise assigned to the same NAME node used to get it from v.

+

A destructuring assignment is performed in program order, or equivalently index order, with each sub-assignment fully completed before beginning the next (a depth-first order). Thus if an assignment with ↩ encounters an error but it's caught with ⎊, some of the assignment may have already been performed, changing variable values.

Modified assignment is the subject assignment rule lhs Derv "↩" subExpr?. In this case, lhs is evaluated as if it were a subExpr (the syntax is a subset of subExpr), and passed as an argument to Derv. The full application is lhs Derv subExpr, if subExpr is given, and Derv lhs otherwise. Its value is assigned to lhs, and is also the result of the modified assignment expression.

Expressions

We now give rules for evaluating an atom, Func, _mod1 or _mod2_ expression (the possible options for ANY). A literal or primitive sl, Fl, _ml, or _cl_ has a fixed value defined by the specification (literals and built-ins). An identifier s, F, _m, or _c_, if not preceded by atom ".", must have an associated variable due to the scoping rules, and returns this variable's value, or causes an error if it has not yet been set. If it is preceded by atom ".", then the atom node is evaluated first; its value must be a namespace, and the result is the value of the identifier's name in the namespace, or an error if the name is undefined. A parenthesized expression such as "(" _modExpr ")" simply returns the result of the interior expression. A braced construct such as BraceFunc is defined by the evaluation of the statements it contains after all parameters are accepted. Finally, a list "⟨" ⋄? ( ( EXPR ⋄ )* EXPR ⋄? )? "⟩" or ANY ( "‿" ANY )+ 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.

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