;;;----- Licensing notice ---------------------------------------------------
;;;
-;;; This file is part of the Sensble Object Design, an object system for C.
+;;; This file is part of the Sensible Object Design, an object system for C.
;;;
;;; SOD is free software; you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published by
failures
:initial-value nil))
+(export 'parse-empty)
+(defun parse-empty (&optional value)
+ "Return a parser which parses nothing, successfully.
+
+ The parser returns VALUE and consumes nothing."
+ (lambda () (values value t nil)))
+
+(export 'parse-fail)
+(defun parse-fail (indicator &optional consumedp)
+ "Return a parser which fails.
+
+ The parser reports the INDICATOR and (falsely) claims to have consumed
+ input if CONSUMEDP is true."
+ (lambda () (values indicator nil consumedp)))
+
;;;--------------------------------------------------------------------------
;;; Basic protocol.
The return value may later be used with `parser-restore-place'. Be
careful: all of this is happening at macro-expansion time.")
(:method (context)
- (error "Parser context ~S doesn't support rewinding." context)))
+ (error "Parser context ~S doesn't support rewinding" context)))
(export 'parser-restore-place)
(defgeneric parser-restore-place (context place)
`(let ((,,place ,(parser-capture-place ,context)))
,(if (parser-places-must-be-released-p ,context)
`(unwind-protect ,(,bodyfunc)
- ,(parser-release-place ,context ,place))
+ (when ,,place
+ ,(parser-release-place ,context ,place)))
(,bodyfunc))))))))
(export 'peek)
"Attempt to run PARSER, but rewind the underlying source if it fails."
(with-gensyms (value win consumedp)
(with-parser-place (place context)
- `(multiple-value-bind (,value ,win ,consumedp) (parse ,parser)
- (cond (,win
- (values ,value ,win ,consumedp))
- (t
- ,(parser-restore-place context place)
- (values ,value ,win nil)))))))
+ `(macrolet ((commit-peeked-place ()
+ `(progn
+ ,',(parser-release-place context place)
+ (setf ,',place nil))))
+ (multiple-value-bind (,value ,win ,consumedp) (parse ,parser)
+ (cond ((or ,win (null ,place))
+ (values ,value ,win ,consumedp))
+ (t
+ ,(parser-restore-place context place)
+ (values ,value ,win nil))))))))
+
+(defun commit-peeked-place ()
+ "Called by `commit' not lexically within `peek'."
+ (error "`commit' is not within `peek'"))
+
+(export 'commit)
+(defparse commit ()
+ "Commit to the current parse.
+
+ This releases the place captured by the innermost lexically enclosing
+ `peek'."
+ '(progn
+ (commit-peeked-place)
+ (values nil t nil)))
;;;--------------------------------------------------------------------------
;;; Character parser context protocol.