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fixed description

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svn: r1330
This commit is contained in:
Matthew Flatt 2005-11-16 20:28:22 +00:00
parent 5854060079
commit ec2567b392
1 changed files with 12 additions and 13 deletions
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collects/algol60/cfg-parser.ss
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@ -3,22 +3,21 @@
;; `parser', except that it works on an arbitrary CFG (returning ;; `parser', except that it works on an arbitrary CFG (returning
;; the first sucecssful parse). ;; the first sucecssful parse).
;; I think this is probably a packrat parser, except that ;; It's a backtracking parser. Alternative for a non-terminal are
;; left-recursion is not transformed away. Instead, alternative ;; computed in parallel, and multiple attempts to compute the same
;; solutions are computed in parallel, and multiple attempts to ;; result block until the first one completes. If you get into
;; compute the same result block until the first one completes. ;; deadlock, such as when trying to match
;; If you get into deadlock, such as when trying to match
;; <foo> := <foo> ;; <foo> := <foo>
;; then it means that there's no successful parse, so everything ;; then it means that there's no successful parse, so everything
;; that's blocked should fail. ;; that's blocked fails.
;; The packrat-ness is caching the series of results for a particular ;; Caching remember the series of results for a particular
;; non-terminal at a particular starting location. Otherwise, it's ;; non-terminal at a particular starting location. Otherwise, the
;; backtracking search. Backtracking is implemented through explicit ;; parser uses backtracking search. Backtracking is implemented
;; success and failure continuations. Multiple results for a ;; through explicit success and failure continuations. Multiple
;; particular nonterminal and location are kept only when they have ;; results for a particular nonterminal and location are kept only
;; different lengths. (Otherwise, in the spirit of finding one ;; when they have different lengths. (Otherwise, in the spirit of
;; successful parse, only the first result is kept.) ;; finding one successful parse, only the first result is kept.)
;; The parser-tools's `parse' is used to transform tokens in the ;; The parser-tools's `parse' is used to transform tokens in the
;; grammar to tokens specific to this parser. In other words, this ;; grammar to tokens specific to this parser. In other words, this