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110 lines
3.1 KiB
Racket
110 lines
3.1 KiB
Racket
#lang racket/base
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;; A language level for automatically generating parsers out of BNF grammars.
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;;
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;; Danny Yoo (dyoo@hashcollision.org)
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;;
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;; Intent: make it trivial to generate languages for Racket. At the
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;; moment, I find it painful to use br-parser-tools. This library is
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;; meant to make it less agonizing.
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;;
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;; The intended use of this language is as follows:
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;;
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;;;;; s-exp-grammar.rkt ;;;;;;;;;
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;; #lang brag
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;; s-exp : "(" s-exp* ")" | ATOM
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; What this generates is:
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;;
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;; * parse: a function that consumes a source and a
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;; position-aware lexer, and produces a syntax object.
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;;
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;; * make-rule-parser: a custom parser given a provided start rule.
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;;
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;; You'll still need to do a little work, by providing a lexer that
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;; defines what the uppercased tokens mean. For example, you can
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;; use the br-parser-tools/lex lexer tools:
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;;
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;; (require brag/support
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;; br-parser-tools/lex
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;; br-parser-tools/lex-sre)
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;;
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;; (define tokenize
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;; (lexer-src-pos
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;; [(:+ alphabetic)
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;; (token 'ATOM lexeme)]
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;; [whitespace
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;; (return-without-pos (tokenize/1 input-port))]
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;; [(:or "(" ")")
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;; (token lexeme lexeme)]))
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;;
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;; However, that should be all you need. The output of an
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;; generated grammar is an honest-to-goodness syntax
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;; object with source locations, fully-labeled by the rules.
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;;
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;; (parse (tokenize an-input-port))
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;;
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;;
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;; The first rule is treated as the start rule; any successful parse
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;; must finish with end-of-file.
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;; Terminology:
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;;
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;; A rule is a rule identifier, followed by a colon ":", followed by a
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;; pattern.
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;; A rule identifier is an identifier that is not in upper case.
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;; A rule identifier should follow the Racket rules for identifiers,
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;; except that it can't contain * or +.
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;;
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;; A token is a rule identifier that is all in upper case.
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;; A pattern may either be
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;;
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;; * an implicit sequence of patterns,
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;;
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;; * a literal string,
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;;
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;; * a rule identifier,
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;;
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;; * a quanitifed pattern, either with "*" or "+",
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;;
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;; * an optional pattern: a pattern surrounded by "[" and "]", or
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;;
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;; * a grouped sequence: a pattern surrounded by "(" and ")".
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(require (for-syntax racket/base
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"codegen.rkt"
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syntax/strip-context))
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(provide rules
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(except-out (all-from-out racket/base) #%module-begin)
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(rename-out [my-module-begin #%module-begin]))
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(define-syntax (my-module-begin module-stx)
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(syntax-case module-stx ()
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[(_ RULES-STX)
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(with-syntax ([RULES-STX (for/fold ([stx #'RULES-STX])
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([sym (in-list '(parse parse-to-datum parse-tree make-rule-parser all-token-types))])
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(syntax-property stx sym (syntax-local-introduce (replace-context module-stx (datum->syntax #f sym)))))])
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#'(#%module-begin
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(provide (all-defined-out))
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RULES-STX))]))
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(define-syntax (rules rules-stx)
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(rules-codegen #:parser-provider-module 'brag/cfg-parser/cfg-parser ;; 'br-parser-tools/yacc
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#:parser-provider-form 'cfg-parser ;; 'parser
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rules-stx))
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