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|
;;;; argot.lisp
(in-package #:argot)
(defstruct rule lhs pattern action)
(define-condition invalid-rule-def (error)
((rule :reader rule :initarg :rule)))
(defun include-rule (grammar rule)
(setf (gethash (rule-lhs rule) grammar) rule))
(defun nonterminal? (lhs)
(and (symbolp lhs)
(let* ((name (symbol-name lhs))
(length (length name)))
(and (<= 3 length)
(eql #\< (elt name 0))
(eql #\> (elt name (1- length)))))))
(defun var? (var)
(and var (symbolp var) (not (keywordp var))))
(defun pattern? (pat)
"Every pattern PAT is either a nonterminal symbol, or a pattern
expression. Such expressions look like (OP . ARGS) where OP is one of
:SEQ :? :* :+ :OR :OR= := :*= :?= :SEQ= :@ :EOF"
(or (nonterminal? pat)
(and (consp pat)
(destructuring-bind (op . more) pat
(case op
((:seq :? :* :+ :or)
(every #'pattern? more))
((:or= := :*= :+= :?= :seq=)
(not (null more)))
(:@ (and (var? (first more))
(not (third more))
(pattern? (second more))))
(:eof (endp more)))))))
(defun var-pattern? (pat)
"VAR-PATTERN? checks that a pattern is a var pattern (:@ VAR PATTERN)
and it returns VAR in that case."
(and (consp pat)
(third pat)
(destructuring-bind (at var . _) pat
(declare (ignore _))
(and (eq at :@) (var? var) var))))
(defun collect-vars (pat)
"Collects all of the variables from the var patterns in PAT and returns them."
(if-let (var (var-pattern? pat))
(list var)
(when (consp pat)
(append (collect-vars (car pat))
(collect-vars (cdr pat))))))
(defun parse-rule-def (ruledef)
(handler-case
(ematch ruledef
((guard (list lhs :-> pattern)
(and (nonterminal? lhs) (pattern? pattern)))
(list lhs pattern (collect-vars pattern) nil))
((guard (list lhs :-> pattern :=> action)
(and (nonterminal? lhs) (pattern? pattern)))
(list lhs pattern (collect-vars pattern) action)))
(trivia::match-error ()
(error 'invalid-rule-def :rule ruledef))))
(defmacro defgrammar (name (&key (documentation "")) &body ruledefs)
(let ((bindings-var (gensym "BINDINGS")))
`(progn
(defvar ,name nil ,documentation)
(setf ,name (make-hash-table :test #'eq))
,@(loop :for ruledef :in ruledefs
:for (lhs pattern vars action) := (parse-rule-def ruledef)
:for bindings
:= (loop :for var :in vars
:collect `(,var (cdr (assoc ',var ,bindings-var))))
:collect `(include-rule
,name
(make-rule
:lhs ',lhs
:pattern ',pattern
,@(when action
(list
:action `(lambda (,bindings-var) (let ,bindings ,action)))))))
,name)))
(defvar *position*)
(defvar *grammar*)
(defvar *tokens*)
(defvar *bindings*)
(defun succeed (result)
(values result t))
(defun fail ()
(values nil nil))
(defparameter +eof+ #())
(defun next-token ()
(if (< *position* (length *tokens*))
(prog1 (elt *tokens* *position*)
(incf *position*))
+eof+))
(defun update-bindings (var value)
(setf *bindings* (acons var value *bindings*)))
(defmacro try-parse
((&optional (result (gensym)))
parse-expression
&optional
(success-clause `(succeed ,result))
(fail-clause '(fail)))
(alexandria:with-gensyms (successp pos)
`(let ((,pos *position*))
(multiple-value-bind (,result ,successp) ,parse-expression
(if ,successp ,success-clause
(progn
(setf *position* ,pos)
,fail-clause))))))
(defun parse-sequence (patterns)
"Parse each member of PATTERNS and succeed with a list of results. If
any pattern fails the whole parse fails."
(try-parse
() (loop :for pattern :in patterns
:for (result successp)
:= (multiple-value-list (parse-pattern pattern))
:if successp
:collect result :into results
:else :return (fail)
:finally (return (succeed results)))))
(defun parse-optional (pattern)
(try-parse
(res) (parse-pattern pattern)
(succeed res)
(succeed nil)))
(defun parse-kleene (pattern)
(loop :for (res successp) := (multiple-value-list (try-parse () (parse-pattern pattern)))
:while successp :collect res :into results
:finally (return-from parse-kleene (succeed results))))
(defun parse-one-or-more (pattern)
(try-parse (first) (parse-pattern pattern)
(try-parse (rest) (parse-kleene pattern)
(succeed (cons first rest)))))
(defun parse-alernatives (patterns)
(if (endp patterns) (fail)
(try-parse (result) (parse-pattern (first patterns))
(succeed result)
(parse-alernatives (rest patterns)))))
(defun literals->patterns (literals)
(loop :for l :in literals :collect (list := l)))
(defun literals-equal? (a b) (eq a b))
(defun parse-literal (literal)
(if (literals-equal? (next-token) literal)
(succeed literal)
(fail)))
(defun parse-literal-alternatives (literals)
(parse-alernatives (literals->patterns literals)))
(defun parse-kleene-literal (literal)
(parse-kleene (list := literal)))
(defun parse-one-or-more-literal (literal)
(parse-one-or-more (list := literal)))
(defun parse-optional-literal (literal)
(parse-optional (list := literal)))
(defun parse-literal-sequence (literals)
(parse-sequence (literals->patterns literals)))
(defun parse-binding-pattern (var pattern)
(try-parse
(result) (parse-pattern pattern)
(progn
(update-bindings var result)
(succeed result))))
(defun parse-eof ()
(if (eq +eof+ (next-token))
(succeed nil)
(fail)))
(defun parse-pattern (pattern)
(try-parse ()
(if (nonterminal? pattern)
(parse-rule pattern)
(destructuring-bind (op . args) pattern
(case op
(:seq (parse-sequence args))
(:? (parse-optional (first args)))
(:* (parse-kleene (first args)))
(:+ (parse-one-or-more (first args)))
(:or (parse-alernatives args))
(:or= (parse-literal-alternatives args))
(:= (parse-literal (first args)))
(:*= (parse-kleene-literal (first args)))
(:+= (parse-one-or-more-literal (first args)))
(:?= (parse-optional-literal (first args)))
(:seq= (parse-literal-sequence args))
(:@ (parse-binding-pattern (first args) (second args)))
(:eof (parse-eof)))))))
(defun parse-rule (nonterminal)
(if-let (rule (gethash nonterminal *grammar*))
(let ((*bindings* nil))
(try-parse (result) (parse-pattern (rule-pattern rule))
(if (rule-action rule)
(succeed (funcall (rule-action rule) *bindings*))
(succeed result))))
(fail)))
(defun parse (grammar rule tokens)
(let ((*position* 0)
(*grammar* grammar)
(*tokens* tokens))
(parse-rule rule)))
|
