From 972a0543c98aa8cd3c2034725397953413c8776e Mon Sep 17 00:00:00 2001 From: Marshall Lochbaum Date: Wed, 1 Dec 2021 21:27:40 -0500 Subject: =?UTF-8?q?Specify=20placeholder=20assignment=20to=20=C2=B7?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- docs/spec/evaluate.html | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'docs/spec/evaluate.html') diff --git a/docs/spec/evaluate.html b/docs/spec/evaluate.html index 5d4a0eb7..e2f40bd1 100644 --- a/docs/spec/evaluate.html +++ b/docs/spec/evaluate.html @@ -18,8 +18,8 @@

Inputs and other names are bound when evaluation of a BODY is begun. Special names are always bound when applicable: ๐•จ๐•ฉ๐•ค if arguments are used, ๐•จ if there is a left argument, ๐•—๐•˜ if operands are used, and _๐•ฃ and _๐•ฃ_ for modifiers and combinators, respectively. Any names in the header are also bound, allowing multiple assignment for arguments.

If there is no left argument, but the BODY contains ๐•จ or ๐•Ž at the top level, then it is conceptually re-parsed with ๐•จ replaced by ยท to give a monadic version before application; this modifies the syntax tree by replacing some instances of subject, arg, or Operand with nothing. The token ๐•Ž is not allowed in this case and causes an error. Re-parsing ๐•จ can also cause an error if it's used as an operand or list element, where nothing is not allowed by the grammar. Note that these errors must not appear if the block is always called with two arguments. True re-parsing is not required, as the same effect can also be achieved dynamically by treating ยท as a value and checking for it during execution. If it's used as a left argument, then the function should instead be called with no left argument (and similarly in trains); if it's used as a right argument, then the function and its left argument are evaluated but rather than calling the function ยท is "returned" immediately; and if it's used in another context then it causes an error.

Assignment

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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.

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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 LHS_NAME, or an lhsList where every LHS_ENTRY is an LHS_NAME or lhs "โ‡" LHS_NAME, so that it can be considered a list of LHS_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 LHS_NAME node used to get it from v.

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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 "ยท" is also possible in place of a NAME, and performs no assignment.

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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 "โ‡" 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.

Modified assignment is the subject assignment rule lhs Derv "โ†ฉ" 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 "โŸจ" โ‹„? ( ( EXPR โ‹„ )* EXPR โ‹„? )? "โŸฉ" or ANY ( "โ€ฟ" 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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