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| -rw-r--r-- | spec/grammar.md | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/spec/grammar.md b/spec/grammar.md index 1f863a1b..7154e706 100644 --- a/spec/grammar.md +++ b/spec/grammar.md @@ -2,10 +2,10 @@ BQN's grammar is given below. All terms except `BraceFunc` `_braceMod` `_braceCo The symbols `v`, `F`, `_m`, and `_c_` are identifier tokens with value, function, modifier, and composition classes respectively. Similarly, `vl`, `Fl`, `_ml`, and `_cl_` refer to value literals (numeric and character literals, or primitives) of those classes. While names in the BNF here follow the identifier naming scheme, this is informative only: syntactic classes are no longer used after parsing and cannot be inspected in a running program. -A program is a list of statements. Almost all statements are expressions. However, valueless results stemming from `ยท`, or `๐จ` in a monadic brace function, can be used as statements but not expressions. +A program is a list of statements. Almost all statements are expressions. However, explicit definitions and valueless results stemming from `ยท`, or `๐จ` in a monadic brace function, can be used as statements but not expressions. PROGRAM = โ? ( ( STMT โ )* STMT โ? )? - STMT = EXPR | nothing + STMT = EXPR | DEF | nothing โ = ( "โ" | "," | \n )+ EXPR = valExpr | FuncExpr | _modExpr | _cmpExp_ @@ -60,6 +60,15 @@ Value expressions are complicated by the possibility of list assignment. We also | v ASGN valExpr | v Derv "โฉ" valExpr โ Modified assignment +In an explicit definition, the left hand side looks like application of a function, modifier, or combinator. As with assignment, it is restricted to a simple form with no extra parentheses. The full list syntax is allowed for arguments. + + DEF = VALDEF | FUNCDEF + VALDEF = valLHS "โ" valExpr + FUNCDEF = FuncLHS "โ" FuncExpr + FuncLHS = F _m + | F _c_ F + valLHS = lhs? ( F | FuncLHS ) lhs + One aspect of BQN grammar is not context-free: determining the syntactic class of a brace definition. The terms `braceVal`, `BraceFunc` `_braceMod` `_braceComp_` all obey the syntax for `BRACED` given below. Then the class is determined by the presence of `๐จ`, `๐ฉ`, `๐`, and `๐` (including alternate class spellings) at the top level, that is, not contained within further pairs of braces. If `๐` is present, it is a `_braceCmp_`; otherwise, if `๐` is present it is a `_braceMod`; otherwise is is a `BraceFunc` if `๐จ` or `๐ฉ` are present and a `braceVal` if no special names appear. BRACED = "{" โ? ( STMT โ )* EXPR โ? "}" |