module Genlex:sig..end
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
| |
Kwd of |
| |
Ident of |
| |
Int of |
| |
Float of |
| |
String of |
| |
Char of |
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.ts 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.