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beautiful-racket/beautiful-racket-ragg/br/ragg/rules/parser.rkt

220 lines
7.0 KiB
Racket

9 years ago
#lang racket/base
(require parser-tools/yacc
parser-tools/lex
racket/list
racket/match
"rule-structs.rkt")
;; A parser for grammars.
(provide tokens
token-LPAREN
token-RPAREN
token-LBRACKET
token-RBRACKET
token-PIPE
token-REPEAT
token-RULE_HEAD
token-ID
token-LIT
token-EOF
grammar-parser
current-source
current-parser-error-handler
[struct-out rule]
[struct-out lhs-id]
[struct-out pattern]
[struct-out pattern-id]
[struct-out pattern-lit]
[struct-out pattern-token]
[struct-out pattern-choice]
[struct-out pattern-repeat]
[struct-out pattern-maybe]
[struct-out pattern-seq])
(define-tokens tokens (LPAREN
RPAREN
LBRACKET
RBRACKET
PIPE
REPEAT
RULE_HEAD
ID
LIT
EOF))
;; grammar-parser: (-> token) -> (listof rule)
(define grammar-parser
(parser
(tokens tokens)
(src-pos)
(start rules)
(end EOF)
(grammar
[rules
[(rules*) $1]]
[rules*
[(rule rules*)
(cons $1 $2)]
[()
'()]]
;; I have a separate token type for rule identifiers to avoid the
;; shift/reduce conflict that happens with the implicit sequencing
;; of top-level rules. i.e. the parser can't currently tell, when
;; it sees an ID, if it should shift or reduce to a new rule.
[rule
[(RULE_HEAD pattern)
(begin
(define trimmed (regexp-replace #px"\\s*:$" $1 ""))
(rule (position->pos $1-start-pos)
(position->pos $2-end-pos)
(lhs-id (position->pos $1-start-pos)
(pos (+ (position-offset $1-start-pos)
(string-length trimmed))
(position-line $1-start-pos)
(position-col $1-start-pos))
trimmed)
$2))]]
[pattern
[(implicit-pattern-sequence PIPE pattern)
(if (pattern-choice? $3)
(pattern-choice (position->pos $1-start-pos)
(position->pos $3-end-pos)
(cons $1 (pattern-choice-vals $3)))
(pattern-choice (position->pos $1-start-pos)
(position->pos $3-end-pos)
(list $1 $3)))]
[(implicit-pattern-sequence)
$1]]
[implicit-pattern-sequence
[(repeatable-pattern implicit-pattern-sequence)
(if (pattern-seq? $2)
(pattern-seq (position->pos $1-start-pos)
(position->pos $2-end-pos)
(cons $1 (pattern-seq-vals $2)))
(pattern-seq (position->pos $1-start-pos)
(position->pos $2-end-pos)
(list $1 $2)))]
[(repeatable-pattern)
$1]]
[repeatable-pattern
[(atomic-pattern REPEAT)
(cond [(string=? $2 "*")
(pattern-repeat (position->pos $1-start-pos)
(position->pos $2-end-pos)
0 $1)]
[(string=? $2 "+")
(pattern-repeat (position->pos $1-start-pos)
(position->pos $2-end-pos)
1 $1)]
[else
(error 'grammar-parse "unknown repetition operator ~e" $2)])]
[(atomic-pattern)
$1]]
[atomic-pattern
[(LIT)
(pattern-lit (position->pos $1-start-pos)
(position->pos $1-end-pos)
(substring $1 1 (sub1 (string-length $1))))]
[(ID)
(if (token-id? $1)
(pattern-token (position->pos $1-start-pos)
(position->pos $1-end-pos)
$1)
(pattern-id (position->pos $1-start-pos)
(position->pos $1-end-pos)
$1))]
[(LBRACKET pattern RBRACKET)
(pattern-maybe (position->pos $1-start-pos)
(position->pos $3-end-pos)
$2)]
[(LPAREN pattern RPAREN)
(relocate-pattern $2 (position->pos $1-start-pos) (position->pos $3-end-pos))]])
(error (lambda (tok-ok? tok-name tok-value start-pos end-pos)
((current-parser-error-handler) tok-ok? tok-name tok-value (position->pos start-pos) (position->pos end-pos))))))
;; relocate-pattern: pattern -> pattern
;; Rewrites the pattern's start and end pos accordingly.
(define (relocate-pattern a-pat start-pos end-pos)
(match a-pat
[(pattern-id _ _ v)
(pattern-id start-pos end-pos v)]
[(pattern-token _ _ v)
(pattern-token start-pos end-pos v)]
[(pattern-lit _ _ v)
(pattern-lit start-pos end-pos v)]
[(pattern-choice _ _ vs)
(pattern-choice start-pos end-pos vs)]
[(pattern-repeat _ _ m v)
(pattern-repeat start-pos end-pos m v)]
[(pattern-maybe _ _ v)
(pattern-maybe start-pos end-pos v)]
[(pattern-seq _ _ vs)
(pattern-seq start-pos end-pos vs)]
[else
(error 'relocate-pattern "Internal error when relocating ~s\n" a-pat)]))
; token-id: string -> boolean
;; Produces true if the id we see should be treated as the name of a token.
;; By convention, tokens are all upper-cased.
(define (token-id? id)
(string=? (string-upcase id)
id))
;; position->pos: position -> pos
;; Coerses position structures from parser-tools/lex to our own pos structures.
(define (position->pos a-pos)
(pos (position-offset a-pos)
(position-line a-pos)
(position-col a-pos)))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; During parsing, we should define the source of the input.
(define current-source (make-parameter #f))
;; When bad things happen, we need to emit errors with source location.
(struct exn:fail:parse-grammar exn:fail (srclocs)
#:transparent
#:property prop:exn:srclocs (lambda (instance)
(exn:fail:parse-grammar-srclocs instance)))
(define current-parser-error-handler
(make-parameter
(lambda (tok-ok? tok-name tok-value start-pos end-pos)
(raise (exn:fail:parse-grammar
(format "Error while parsing grammar near: ~e [line=~a, column=~a, position=~a]"
tok-value
(pos-line start-pos)
(pos-col start-pos)
(pos-offset start-pos))
(current-continuation-marks)
(list (srcloc (current-source)
(pos-line start-pos)
(pos-col start-pos)
(pos-offset start-pos)
(if (and (number? (pos-offset end-pos))
(number? (pos-offset start-pos)))
(- (pos-offset end-pos)
(pos-offset start-pos))
#f))))))))