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#cs
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(module input-file-parser mzscheme
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;; routines for parsing the input to the parser generator and producing a
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;; grammar (See grammar.ss)
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(require "yacc-helper.ss" "terminal-syntax.ss" "grammar.ss" (lib "list.ss"))
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(provide parse-input)
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;; get-args: num * syntax-object -> syntax-object list
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(define (get-args x act)
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(let loop ((i 1))
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(cond
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((> i x) null)
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(else (cons (datum->syntax-object act (string->symbol (format "$~a" i)))
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(loop (add1 i)))))))
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;; nullable: production list * int -> non-term set
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;; determines which non-terminals can derive epsilon
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(define (nullable prods num-nts)
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(letrec ((nullable (make-vector num-nts #f))
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(added #f)
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;; possible-nullable: producion list -> production list
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;; Removes all productions that have a terminal
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(possible-nullable
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(lambda (prods)
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(filter (lambda (prod)
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(vector-andmap non-term? (prod-rhs prod)))
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prods)))
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;; set-nullables: production list -> production list
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;; makes one pass through the productions, adding the ones
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;; known to be nullable now to nullable and returning a list
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;; of productions that we don't know about yet.
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(set-nullables
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(lambda (prods)
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(cond
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((null? prods) null)
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((vector-ref nullable
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(gram-sym-index (prod-lhs (car prods))))
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(set-nullables (cdr prods)))
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((vector-andmap (lambda (nt)
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(vector-ref nullable (gram-sym-index nt)))
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(prod-rhs (car prods)))
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(vector-set! nullable
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(gram-sym-index (prod-lhs (car prods)))
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#t)
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(set! added #t)
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(set-nullables (cdr prods)))
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(else
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(cons (car prods)
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(set-nullables (cdr prods))))))))
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(let loop ((P (possible-nullable prods)))
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(cond
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((null? P) nullable)
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(else
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(set! added #f)
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(let ((new-P (set-nullables P)))
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(if added
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(loop new-P)
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nullable)))))))
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;; Given the list of terminal symbols and the precedence/associativity definitions,
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;; builds terminal structures (See grammar.ss)
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;; build-terms: symbol list * symbol list list -> term list
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(define (build-terms term-list precs)
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(let ((counter 0)
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;;(term-list (cons (gensym) term-list))
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;; Will map a terminal symbol to its precedence/associativity
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(prec-table (make-hash-table)))
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;; Fill the prec table
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(for-each
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(lambda (p-decl)
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(begin0
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(let ((assoc (car p-decl)))
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(for-each
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(lambda (term-sym)
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(hash-table-put! prec-table term-sym (make-prec counter assoc)))
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(cdr p-decl)))
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(set! counter (add1 counter))))
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precs)
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(set! counter 0)
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;; Build the terminal structures
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(map
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(lambda (term-sym)
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(begin0
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(make-term term-sym
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counter
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(hash-table-get prec-table term-sym (lambda () #f)))
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(set! counter (add1 counter))))
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term-list)))
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;; Retrieves the terminal symbols from a terminals-def (See terminal-syntax.xx)
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;; get-terms-from-def: syntax-object -> symbol list
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(define (get-terms-from-def term-syn)
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(let ((t (syntax-local-value term-syn (lambda () #f))))
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(cond
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((terminals-def? t) (terminals-def-t t))
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(else
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(raise-syntax-error
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'parser-tokens
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"undefined token group"
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term-syn)))))
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;; parse-input: syntax-object^4 * string -> grammar
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(define (parse-input start term-defs prec-decls prods runtime)
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(let* ((counter 0)
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(start-sym (syntax-object->datum start))
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;; Get the list of terminals out of input-terms
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(list-of-terms
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(syntax-case term-defs ()
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((term-def ...)
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(andmap identifier? (syntax->list term-defs))
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(remove-duplicates
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(apply append
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(map get-terms-from-def
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(syntax->list term-defs)))))
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(_
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(raise-syntax-error
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'parser-tokens
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"Token list must be (symbol ...)"
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term-defs))))
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(list-of-non-terms
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(syntax-case prods ()
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(((non-term production ...) ...)
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(begin
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(for-each
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(lambda (nts)
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(if (memq (syntax-object->datum nts) list-of-terms)
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(raise-syntax-error
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'parser-non-terminals
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(format "~a used as both token and non-terminal"
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(syntax-object->datum nts))
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nts)))
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(syntax->list (syntax (non-term ...))))
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(if (not (memq start-sym
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(syntax-object->datum (syntax (non-term ...)))))
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(raise-syntax-error
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'parser-start
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(format "Start symbol ~a not defined as a non-terminal"
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start-sym)
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start))
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(let ((dup (duplicate-list? (syntax-object->datum
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(syntax (non-term ...))))))
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(if dup
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(raise-syntax-error
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'parser-non-terminals
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(format "non-terminal ~a defined multiple times"
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dup)
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prods)))
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(syntax-object->datum (syntax (non-term ...)))))
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(_
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(raise-syntax-error
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'parser-productions
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"Productions must be of the form ((non-terminal productions ...) ...)"
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prods))))
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;; Check the precedence declarations for errors and turn them into data
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(precs
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(syntax-case prec-decls ()
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(((type term ...) ...)
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(let ((p-terms
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(apply append (syntax-object->datum
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(syntax ((term ...) ...))))))
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(cond
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((duplicate-list? p-terms) =>
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(lambda (d)
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(raise-syntax-error
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'parser-precedences
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(format "duplicate precedence declaration for token ~a"
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d)
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prec-decls)))
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(else
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(for-each
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(lambda (a)
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(for-each
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(lambda (t)
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(if (not (memq (syntax-object->datum t)
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list-of-terms))
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(raise-syntax-error
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'parser-precedences
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(format
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"Precedence declared for non-token ~a"
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(syntax-object->datum t))
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t)))
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(syntax->list a)))
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(syntax->list (syntax ((term ...) ...))))
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(for-each
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(lambda (type)
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(if (not (memq (syntax-object->datum type)
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`(left right nonassoc)))
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(raise-syntax-error
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'parser-precedences
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"Associativity must be left, right or nonassoc"
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type)))
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(syntax->list (syntax (type ...))))
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(syntax-object->datum prec-decls)))))
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(_
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(raise-syntax-error
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'parser-precedences
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"Precedence declaration must be of the form ((assoc term ...) ...) where assoc is left, right or nonassoc"
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prec-decls))))
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(terms (build-terms list-of-terms precs))
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(non-terms (begin
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(set! counter 1)
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(map (lambda (non-term)
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(begin0
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(make-non-term non-term counter)
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(set! counter (add1 counter))))
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list-of-non-terms)))
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(term-table (make-hash-table))
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(non-term-table (make-hash-table)))
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(for-each (lambda (t)
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(hash-table-put! term-table (gram-sym-symbol t) t))
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terms)
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(for-each (lambda (nt)
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(hash-table-put! non-term-table (gram-sym-symbol nt) nt))
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non-terms)
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(set! counter 1)
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(let* (
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;; parse-prod: syntax-object -> gram-sym vector
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(parse-prod
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(lambda (prod-so)
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(syntax-case prod-so ()
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((prod-rhs-sym ...)
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(andmap identifier? (syntax->list prod-so))
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(list->vector
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(map (lambda (s)
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(hash-table-get
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term-table
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(syntax-object->datum s)
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(lambda ()
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(hash-table-get
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non-term-table
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(syntax-object->datum s)
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(lambda ()
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(raise-syntax-error
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'parser-production-rhs
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(format
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"~a is not declared as a terminal or non-terminal"
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(syntax-object->datum s))
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s))))))
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(syntax->list prod-so))))
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(_
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(raise-syntax-error
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'parser-production-rhs
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"production right-hand-side must have form (symbol ...)"
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prod-so)))))
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;; parse-action: gram-sym vector * syntax-object -> syntax-object
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(parse-action
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(lambda (prod act)
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(datum->syntax-object
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runtime
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`(lambda ,(get-args (vector-length prod) act)
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,act)
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act)))
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;; parse-prod+action: non-term * syntax-object -> production
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(parse-prod+action
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(lambda (nt prod-so)
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(syntax-case prod-so (prec)
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((prod-rhs action)
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(let ((p (parse-prod (syntax prod-rhs))))
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(begin0
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(make-prod
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nt
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p
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counter
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(let loop ((i (sub1 (vector-length p))))
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(if (>= i 0)
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(let ((gs (vector-ref p i)))
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(if (term? gs)
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(term-prec gs)
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(loop (sub1 i))))
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#f))
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(parse-action p (syntax action)))
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(set! counter (add1 counter)))))
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((prod-rhs (prec term) action)
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(identifier? (syntax term))
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(let ((p (parse-prod (syntax prod-rhs))))
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(begin0
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(make-prod
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nt
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p
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counter
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(term-prec
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(hash-table-get
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term-table
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(syntax-object->datum (syntax term))
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(lambda ()
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(raise-syntax-error
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'parser-production-rhs
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(format
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"unrecognized terminal ~a in precedence declaration"
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(syntax-object->datum (syntax term)))
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(syntax term)))))
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(parse-action p (syntax action)))
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(set! counter (add1 counter)))))
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(_
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(raise-syntax-error
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'parser-production-rhs
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"production must have form [(symbol ...) expression] or [(symbol ...) (prec symbol) expression]"
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prod-so)))))
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;; parse-prod-for-nt: syntax-object -> production list
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(parse-prods-for-nt
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(lambda (prods-so)
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(syntax-case prods-so ()
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((nt productions ...)
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(> (length (syntax->list (syntax (productions ...)))) 0)
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(let* ((prods (syntax-e prods-so))
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(nt (hash-table-get non-term-table
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(syntax-e (car prods)))))
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(map (lambda (p) (parse-prod+action nt p))
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(cdr prods))))
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(_
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(raise-syntax-error
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'parser-productions
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"A production for a non-terminal must be (non-term right-hand-side ...) with at least 1 right hand side"
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prods-so))))))
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(let* ((start (make-non-term 'Start 0))
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(prods
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(cons
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(list (make-prod start
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(vector (hash-table-get non-term-table
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start-sym))
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0
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#f
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(datum->syntax-object
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runtime
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`(lambda (x) x))))
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(map parse-prods-for-nt (syntax->list prods))))
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(nulls (nullable (apply append prods)
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(add1 (length non-terms)))))
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|
(printf "nullable: {~a}~n~n"
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|
|
(apply string-append
|
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|
|
(let loop ((i 0))
|
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|
|
(cond
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|
((>= i (vector-length nulls)) null)
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|
((vector-ref nulls i)
|
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|
(cons
|
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|
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|
(format "~a"
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|
(gram-sym-symbol
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|
(list-ref (cons start non-terms) i)))
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|
(loop (add1 i))))
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(else (loop (add1 i)))))))
|
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|
(make-grammar
|
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|
(list->vector prods)
|
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|
|
|
(apply append prods)
|
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|
|
|
nulls
|
|
|
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|
(cons start non-terms)
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|
terms
|
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|
counter))))))
|
