Strip the copy-and-paste for cfg-parser, keeping the delta vs. parser.

original commit: 4dfe4097720f52968a60f37e2bd8de99b969107c

collects/parser-tools/parser-tools.scrbl

@@ -693,8 +693,6 @@ the right choice when using @racket[lexer] in other situations.
 
 @racketmodname[parser-tools/cfg-parser] provides another parser
 generator as an alternative to @racketmodname[parser-tools/yacc].
-Unlike @racket[parser], @racket[cfg-parser] can consume ambiguous grammars.
-Its interface is a subset of @racketmodname[parser-tools/yacc].
 
 @defform/subs[#:literals (grammar tokens start end precs src-pos
                           suppress debug yacc-output prec)
@@ -708,135 +706,22 @@ Its interface is a subset of @racketmodname[parser-tools/yacc].
                        (end token-id ...)
                        (@#,racketidfont{error} expr)
                        (src-pos)])]{
-    Creates a parser.  The clauses may be in any order, as long as there
-    are no duplicates and all non-@italic{OPTIONAL} declarations are
-    present:
+    Creates a parser similar to that of @racket[parser].  Unlike @racket[parser],
+    @racket[cfg-parser] can consume ambiguous grammars.
+    Its interface is a subset of @racketmodname[parser-tools/yacc].
+    The major differences in the interface are:
                                         
     @itemize[
 
-      @item{@racketblock0[(grammar (non-terminal-id
-                                    ((grammar-id ...) maybe-prec expr)
-                                    ...)
-                                   ...)]
-
-      Declares the grammar to be parsed.  Each @racket[grammar-id] can
-      be a @racket[token-id] from a @racket[group-id] named in a
-      @racket[tokens] declaration, or it can be a
-      @racket[non-terminal-id] declared in the @racket[grammar]
-      declaration.  The @racket[expr] is a
-      ``semantic action,'' which is evaluated when the input is found
-      to match its corresponding production.
-
-      Each action is Racket code that has the same scope as its
-      parser's definition, except that the variables @racket[$1], ...,
-      @racketidfont{$}@math{i} are bound, where @math{i} is the number
-      of @racket[grammar-id]s in the corresponding production. Each
-      @racketidfont{$}@math{k} is bound to the result of the action
-      for the @math{k}@superscript{th} grammar symbol on the right of
-      the production, if that grammar symbol is a non-terminal, or the
-      value stored in the token if the grammar symbol is a terminal.
-      If the @racket[src-pos] option is present in the parser, then
-      variables @racket[$1-start-pos], ...,
-      @racketidfont{$}@math{i}@racketidfont{-start-pos} and
-      @racket[$1-end-pos], ...,
-      @racketidfont{$}@math{i}@racketidfont{-end-pos} and are also
-      available, and they refer to the position structures
-      corresponding to the start and end of the corresponding
-      @racket[grammar-symbol]. Grammar symbols defined as empty-tokens
-      have no @racketidfont{$}@math{k} associated, but do have
-      @racketidfont{$}@math{k}@racketidfont{-start-pos} and
-      @racketidfont{$}@math{k}@racketidfont{-end-pos}.
-      Also @racketidfont{$n-start-pos} and @racketidfont{$n-end-pos}
-      are bound to the largest start and end positions, (i.e.,
-      @racketidfont{$}@math{i}@racketidfont{-start-pos} and
-      @racketidfont{$}@math{i}@racketidfont{-end-pos}).
-
-      An @tech{error production} can be defined by providing
-      a production of the form @racket[(error α)], where α is a
-      string of grammar symbols, possibly empty.
-      
-      All of the productions for a given non-terminal must be grouped
-      with it. That is, no @racket[non-terminal-id] may appear twice
-      on the left hand side in a parser.}
-
-
-      @item{@racket[(tokens group-id ...)]
-
-      Declares that all of the tokens defined in each
-      @racket[group-id]---as bound by @racket[define-tokens] or
-      @racket[define-empty-tokens]---can be used by the parser in the
-      @racket[grammar] declaration.}
-
-
       @item{@racket[(start non-terminal-id)]
       
-      Declares a starting non-terminal for the grammar.
-      
-      Note: unlike @racket[parser], @racket[cfg-parser] does not
-      currently support multiple starting non-terminals
-      for the grammar.}
+      Unlike @racket[parser], @racket[cfg-parser] only allows for
+      a single non-terminal-id.}
                        
-
-      @item{@racket[(end token-id ...)]
-
-      Specifies a set of tokens from which some member must follow any
-      valid parse.  For example, an EOF token would be specified for a
-      parser that parses entire files and a newline token for a parser
-      that parses entire lines individually.}
-
-
-      @item{@racket[(@#,racketidfont{error} expr)]
-
-      The @racket[expr] should evaluate to a function which will be
-      executed for its side-effect whenever the parser encounters an
-      error.
-
-      If the @racket[src-pos] declaration is present, the function
-      should accept 5 arguments,:
-
-      @racketblock[(lambda (tok-ok? tok-name tok-value _start-pos _end-pos) 
-                     ....)]
-
-      Otherwise it should accept 3:
-
-      @racketblock[(lambda (tok-ok? tok-name tok-value) 
-                     ....)]
-
-      The first argument will be @racket[#f] if and only if the error
-      is that an invalid token was received.  The second and third
-      arguments will be the name and the value of the token at which
-      the error was detected.  The fourth and fifth arguments, if
-      present, provide the source positions of that token.}
-
-
-      @item{@racket[(src-pos)] @italic{OPTIONAL}
-
-      Causes the generated parser to expect input in the form
-      @racket[(make-position-token _token _start-pos _end-pos)] instead
-      of simply @racket[_token].  Include this option when using the
-      parser with a lexer generated with @racket[lexer-src-pos].}
+      @item{@racket[cfg-parser] does not support the @racket[precs], 
+             @racket[suppress], @racket[debug], or @racket[yacc-output]
+             options of @racket[parser].}
    ]
-
-    The result of a @racket[parser] expression with one @racket[start]
-    non-terminal is a function, @racket[_parse], that takes one
-    argument.  This argument must be a zero argument function,
-    @racket[_gen], that produces successive tokens of the input each
-    time it is called.  If desired, the @racket[_gen] may return
-    symbols instead of tokens, and the parser will treat symbols as
-    tokens of the corresponding name (with @racket[#f] as a value, so
-    it is usual to return symbols only in the case of empty tokens).
-    The @racket[_parse] function returns the value associated with the
-    parse tree by the semantic actions.  If the parser encounters an
-    error, after invoking the supplied error function, it will try to
-    use @tech{error production}s to continue parsing.  If it cannot, it
-    raises @racket[exn:fail:read].
-
-
-    Each time the Racket code for a @racket[cfg-parser] is compiled
-    (e.g. when a @filepath{.rkt} file containing a @racket[cfg-parser] form
-    is loaded), the parser generator is run.  To avoid this overhead
-    place the parser into a module and compile the module to a
-    @filepath{.zo} bytecode file.
                                              }