bionic (3) Genlex.3o.gz

NAME

       Genlex - A generic lexical analyzer.

Module

       Module   Genlex

Documentation

       Module Genlex
        : sig end

       A generic lexical analyzer.

       This  module  implements  a  simple  'standard'  lexical analyzer, presented as a function from character
       streams to token streams. It implements roughly the lexical conventions of OCaml, but is parameterized by
       the set of keywords of your language.

       Example:   a   lexer   suitable   for   a   desk  calculator  is  obtained  by  let  lexer  =  make_lexer
       ["+";"-";"*";"/";"let";"="; ( ; ) ]

       The associated parser would be a function from token stream to, for instance, int , and would have  rules
       such as:

       let  rec  parse_expr  =  parser  |  [< n1 = parse_atom; n2 = parse_remainder n1 >] -> n2 and parse_atom =
       parser | [< 'Int n >] -> n | [< 'Kwd ( ; n = parse_expr; 'Kwd ) >] -> n and parse_remainder n1 = parser |
       [< 'Kwd + ; n2 = parse_expr >] -> n1+n2 | [< >] -> n1

       One  should  notice  that  the  use  of  the  parser keyword and associated notation for streams are only
       available through camlp4 extensions. This means that one has to preprocess its sources e. g. by using the
       -pp command-line switch of the compilers.

       type token =
        | Kwd of string
        | Ident of string
        | Int of int
        | Float of float
        | String of string
        | Char of char

       The type of tokens. The lexical classes are: Int and Float for integer and floating-point numbers; String
       for string literals, enclosed in double quotes; Char for character literals, enclosed in  single  quotes;
       Ident  for  identifiers  (either  sequences  of  letters, digits, underscores and quotes, or sequences of
       'operator characters' such as + , * , etc); and Kwd for keywords (either identifiers or  single  'special
       characters' such as ( , } , etc).

       val make_lexer : string list -> char Stream.t -> token Stream.t

       Construct  the lexer function. The first argument is the list of keywords. An identifier s is returned as
       Kwd s if s belongs to this list, and as Ident s otherwise.  A special character s is returned as Kwd s if
       s  belongs  to  this list, and cause a lexical error (exception Stream.Error with the offending lexeme as
       its parameter) otherwise.  Blanks and newlines are skipped. Comments delimited by (* and *)  are  skipped
       as  well,  and  can  be  nested.  A  Stream.Failure  exception is raised if end of stream is unexpectedly
       reached.