74 lines
3.5 KiB
OCaml
74 lines
3.5 KiB
OCaml
(**************************************************************************)
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(* *)
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(* OCaml *)
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(* *)
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(* Xavier Leroy, projet Cristal, INRIA Rocquencourt *)
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(* *)
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(* Copyright 1996 Institut National de Recherche en Informatique et *)
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(* en Automatique. *)
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(* *)
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(* All rights reserved. This file is distributed under the terms of *)
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(* the GNU Lesser General Public License version 2.1, with the *)
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(* special exception on linking described in the file LICENSE. *)
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(* *)
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(**************************************************************************)
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(** A generic lexical analyzer.
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This module implements a simple 'standard' lexical analyzer, presented
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as a function from character streams to token streams. It implements
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roughly the lexical conventions of OCaml, but is parameterized by the
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set of keywords of your language.
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Example: a lexer suitable for a desk calculator is obtained by
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{[ let lexer = make_lexer ["+";"-";"*";"/";"let";"="; "("; ")"] ]}
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The associated parser would be a function from [token stream]
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to, for instance, [int], and would have rules such as:
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{[
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let rec parse_expr = parser
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| [< n1 = parse_atom; n2 = parse_remainder n1 >] -> n2
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and parse_atom = parser
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| [< 'Int n >] -> n
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| [< 'Kwd "("; n = parse_expr; 'Kwd ")" >] -> n
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and parse_remainder n1 = parser
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| [< 'Kwd "+"; n2 = parse_expr >] -> n1+n2
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| [< >] -> n1
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]}
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One should notice that the use of the [parser] keyword and associated
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notation for streams are only available through camlp4 extensions. This
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means that one has to preprocess its sources {i e. g.} by using the
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["-pp"] command-line switch of the compilers.
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*)
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(** The type of tokens. The lexical classes are: [Int] and [Float]
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for integer and floating-point numbers; [String] for
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string literals, enclosed in double quotes; [Char] for
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character literals, enclosed in single quotes; [Ident] for
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identifiers (either sequences of letters, digits, underscores
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and quotes, or sequences of 'operator characters' such as
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[+], [*], etc); and [Kwd] for keywords (either identifiers or
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single 'special characters' such as [(], [}], etc). *)
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type token =
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Kwd of string
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| Ident of string
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| Int of int
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| Float of float
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| String of string
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| Char of char
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val make_lexer : string list -> char Stream.t -> token Stream.t
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(** Construct the lexer function. The first argument is the list of
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keywords. An identifier [s] is returned as [Kwd s] if [s]
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belongs to this list, and as [Ident s] otherwise.
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A special character [s] is returned as [Kwd s] if [s]
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belongs to this list, and cause a lexical error (exception
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{!Stream.Error} with the offending lexeme as its parameter) otherwise.
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Blanks and newlines are skipped. Comments delimited by [(*] and [*)]
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are skipped as well, and can be nested. A {!Stream.Failure} exception
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is raised if end of stream is unexpectedly reached.*)
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