parser.rkt

#lang racket/base

(require parser-tools/yacc
         parser-tools/lex
         "lexer.rkt")


; (struct srcloc (source line column position span))
(define (positions->srcloc start-pos end-pos)
  (srcloc #f
          (position-line start-pos)
          (position-col start-pos)
          (position-offset start-pos)
          (- (position-offset end-pos) (position-offset start-pos))))

; docs for datum->syntax
; https://docs.racket-lang.org/reference/stxops.html#%28def._%28%28quote._~23~25kernel%29._datum-~3esyntax%29%29
(define (position-token->syntax val start-pos end-pos)
  (datum->syntax #f val (positions->srcloc start-pos end-pos)))

(define sample-parser
  (parser
   [start exprs]
   [end EOF]
   [error void]
   [src-pos]
   [tokens basic-tokens punct-tokens]
   ; precs clause go from lowest to highest priority
   ; tokens at the same level share the same priority
   [precs (left ADD SUBTRACT)
          (left MULTIPLY DIVIDE)]
   [grammar
    [exprs 
     [(expr exprs) `(values ,$1 ,$2)]
     [(expr) $1]]
          ; the start position of a parenthesized expression is the start position of the open '('
    [expr [(LPAREN expr RPAREN) (position-token->syntax $2 $1-start-pos $3-end-pos)] 
          ; the start position of a number is the start position of the number token
          [(NUM) (position-token->syntax $1 $1-start-pos $1-end-pos)]
          ; the start position of all binary expression is the start position of the first expression
          ; the end position is the end position of the second expression
          [(expr MULTIPLY expr) (position-token->syntax `(multiply ,$1 ,$3) $1-start-pos $3-end-pos)]
          [(expr DIVIDE expr) (position-token->syntax `(divide ,$1 ,$3) $1-start-pos $3-end-pos)]
          [(expr SUBTRACT expr) (position-token->syntax `(subtract ,$1 ,$3) $1-start-pos $3-end-pos)]
          [(expr ADD expr) (position-token->syntax `(add ,$1 ,$3) $1-start-pos $3-end-pos)]
    ]]))

(provide sample-parser)