From fb3580660898306105c2e1f041f29bbdb9006210 Mon Sep 17 00:00:00 2001 From: Marshall Lochbaum Date: Mon, 29 Nov 2021 20:55:22 -0500 Subject: =?UTF-8?q?Remove=20return=20(=E2=86=92)=20from=20the=20spec?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- docs/spec/evaluate.html | 3 +-- docs/spec/grammar.html | 4 +--- docs/spec/scope.html | 2 -- docs/spec/token.html | 2 +- 4 files changed, 3 insertions(+), 8 deletions(-) (limited to 'docs/spec') diff --git a/docs/spec/evaluate.html b/docs/spec/evaluate.html index 9b57dd5f..44a337b5 100644 --- a/docs/spec/evaluate.html +++ b/docs/spec/evaluate.html @@ -7,7 +7,7 @@

Specification: BQN evaluation

This page describes the semantics of the code constructs whose grammar is given in grammar.md. 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.

Here we assume that the referent of each identifier, or equivalently the connections between identifiers, have been identified according to the scoping rules.

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Evaluation is an ordered process, and any actions required to evaluate a node always have a specified order unless performing them in any order would have the same effect. Side effects that are relevant to ordering are setting and getting the value of a variable, causing an error, and returning (with →) from a block. Errors described in this page are "evaluation errors" and can be caught by the Catch (⎊) modifier. For caught errors and returns, evaluation halts without attempting to complete any in-progress node, and is restarted by Catch (for errors) or at the end of the appropriate block evaluation (for returns).

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Evaluation is an ordered process, and any actions required to evaluate a node always have a specified order unless performing them in any order would have the same effect. Side effects that are relevant to ordering are setting and getting the value of a variable, and causing an error. Errors described in this page are "evaluation errors" and can be caught by the Catch (⎊) modifier. If caught, evaluation halts without attempting to complete any in-progress node, and is restarted by Catch.

As specified, BQN programs can involve an arbitrary amount of information, but when run there will be memory and possibly other limitations. To accommodate this, any part of evaluation can cause an error, if a resource such as memory, stack memory, or limited execution time is exhausted.

Programs and blocks

The result of parsing a valid BQN program is a PROGRAM, and the program is run by evaluating this term.

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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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A Return node creates a return function. As discussed in the scoping rules, its identifier indicates a namespace from a particular block evaluation. When called, the function causes an error if that block has finished execution, or if the call includes a left argument 𝕨. Otherwise, evaluation stops immediately, and resumes at the end of the block where it returns the right argument 𝕩 from that block.

Rules in the table below are function and modifier evaluation.

diff --git a/docs/spec/grammar.html b/docs/spec/grammar.html index 99058319..d28fa55b 100644 --- a/docs/spec/grammar.html +++ b/docs/spec/grammar.html @@ -32,12 +32,10 @@ |Operand_mod2_# Left partial application |_mASGN_m1Expr -

Functions can be formed by fully applying modifiers, as trains, or with the return token →, which behaves syntactically like a 1-modifier whose operand must be an identifier. Modifiers are left-associative, so that the left operand (Operand) can include modifier applications but the right operand (subject | Func) cannot. Trains are right-associative, but bind less tightly than modifiers. Assignment is not allowed in the top level of a train: it must be parenthesized.

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Functions can be formed by fully applying modifiers or as trains. Modifiers are left-associative, so that the left operand (Operand) can include modifier applications but the right operand (subject | Func) cannot. Trains are right-associative, but bind less tightly than modifiers. Assignment is not allowed in the top level of a train: it must be parenthesized.

Derv     = Func
          | Operand _mod1
          | Operand _mod2_ ( subject | Func )
-         | Return
-Return   = ( NAME | "𝕊" | "𝕣" ) "→"
 Operand  = subject
          | Derv
 Fork     = Derv
diff --git a/docs/spec/scope.html b/docs/spec/scope.html
index 5576f6c8..a4663def 100644
--- a/docs/spec/scope.html
+++ b/docs/spec/scope.html
@@ -30,5 +30,3 @@
 
When a body in a block is evaluated, it creates a namespace, which contains a variable for each definition (that is, defined identifier instance) the body contains. Whenever another block—the block itself, not its contents—is evaluated during the execution of the block, it is linked to the currently-evaluating block, so that it will use the variables defined in this instance. By following these links repeatedly, an instance of a block is always linked to exactly one instance of each block that contains it. These links form a tree that is not necessarily related to the call stack of functions and modifiers. Using the links, the variable an identifier refers to is the one corresponding to that variable's definition in the linked instance of the containing scope for the definition.

 
The first access to a variable must be made by its definition (this also means it sets the variable). If a different instance of its identifier accesses it first, then an error results. This can happen because every scope contained in a particular scope sees all the definitions it uses, and such a scope could be called before the definition is run. Because of conditional execution, this property must be checked at run time in general; however, in cases where it is possible to statically determine that a program will always violate it, a BQN instance can give an error at compile time rather than run time.

 
A namespace defines a mapping from names to variables: if the given name is shared by an exported identifier in the body used to create that namespace, then that name maps to the variable corresponding to that identifier. The mapping is undefined for other names.

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Returns

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The name NAME | "𝕊" | "𝕣" in a Return node is resolved exactly like any other identifier. Following resolution, the block that defines the identifier must not be a namespace block (export variables or contain an EXPORT statement). Furthermore, if it is a NAME, then its definition must be an internal name for a containing block: s in brSub, F in FuncHead or FMain, _m in Mod1H1 or _mMain, or _c_ in Mod2H1 or _cMain_. When reached, the Return node's identifier is not accessed; instead, it is used to indicate the namespace that contains it, and through this the block evaluation that created that namespace.

diff --git a/docs/spec/token.html b/docs/spec/token.html
index acf8dc4b..b935b9b9 100644
--- a/docs/spec/token.html
+++ b/docs/spec/token.html
@@ -43,7 +43,7 @@
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Punctuation←⇐↩→(){}⟨⟩‿⋄,. and newline←⇐↩(){}⟨⟩‿⋄,. and newline
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