package batteries

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package batteries
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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 parse_expr = parser
    [< 'Int n >] -> n
               | [< 'Kwd "("; n = parse_expr; 'Kwd ")" >] -> n
               | [< n1 = parse_expr; n2 = parse_remainder n1 >] -> n2
and parse_remainder n1 = parser
    [< 'Kwd "+"; n2 = parse_expr >] -> n1+n2
                       | ...
  • author Jacques Garrigue
  • author David Teller
type token = Genlex.token =
  1. | Kwd of string
  2. | Ident of string
  3. | Int of int
  4. | Float of float
  5. | String of string
  6. | 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 Parse_error) otherwise. Blanks and newlines are skipped. Comments delimited by (* and *) are skipped as well, and can be nested.

type lexer_error =
  1. | IllegalCharacter of char
  2. | NotReallyAChar
  3. | NotReallyAnEscape
  4. | EndOfStream
exception LexerError of lexer_error * int
type t

A lexer

val of_list : string list -> t

Create a lexer from a list of keywords

val to_stream_filter : t -> char Stream.t -> token Stream.t

Apply the lexer to a stream.

val to_enum_filter : t -> char BatEnum.t -> token BatEnum.t

Apply the lexer to an enum.

val to_lazy_list_filter : t -> char BatLazyList.t -> token BatLazyList.t

Apply the lexer to a lazy list.

val string_of_token : token -> string
Extending to other languages
module Languages : sig ... end