* [Caml-list] explain this Genlex behavior
@ 2001-04-26 23:53 Chris Hecker
0 siblings, 0 replies; only message in thread
From: Chris Hecker @ 2001-04-26 23:53 UTC (permalink / raw)
To: caml-list
I was writing a parser with Genlex, and came across strange behavior.
I was trying to parse two numbers separated by a colon (:), but it was
failing when the second number was negative. So, "1.0:1.0" would
parse, but "1.0:-1.0" would not. I know about the greedy lexing of
minus (-) to the number, and in fact that should help me here. The
strange thing is a semi-colon works fine, so "1.0;-1.0" parses.
I decided to figure out which characters worked and which didn't.
Here's the output of the program below:
# test_it ();;
Passed: } { ` _ ] [ ; . , ) (
Failed: ~ | ^ \ @ ? > = < : / - + * ' & % $ # " !
Passed: ~ } | { ` _ ^ ] \ [ @ ? > = < ; : / . - , + * ) ( & % $ # !
Failed: ' "
The first pair of pass/fails are for no space between the separator,
so "n:-n", etc. The second pair are with a space "n: -n".
What's the deal here?
Chris
----------------
open Genlex
(* make a simple expression parser for "n?n" where "?" is a
parameterized separator *)
let do_it sep space =
let s = "1.0" ^ sep ^ space ^ "-2.0" in
let rec parse_it = parser
[< num1 = parse_num; 'Kwd sep ; num2 = parse_num >] -> num1,num2
and parse_num = parser
[< 'Float f1 >] -> f1
| [< 'Int i1 >] -> float i1 in
let lex = make_lexer [sep] in
parse_it (lex(Stream.of_string s))
let seps = [
"!"; "\""; "#"; "$"; "%"; "&"; "'"; "("; ")"; "*"; "+"; ",";
"-"; "."; "/"; ":"; ";"; "<"; "="; ">"; "?"; "@"; "["; "\\"; "]";
"^"; "_"; "`"; "{"; "|"; "}"; "~";]
let test_it () =
let do_test s =
let pass,fail = ref [],ref [] in
List.iter
~f:(fun el ->
try
ignore (do_it el s);
pass := el :: !pass;
with _ ->
fail := el :: !fail
) seps;
print_string "Passed: ";
List.iter ~f:(fun el -> Printf.printf "%s " el) !pass;
print_string "\nFailed: ";
List.iter ~f:(fun el -> Printf.printf "%s " el) !fail;
print_newline ()
in
do_test "";
do_test " "
-------------------
To unsubscribe, mail caml-list-request@inria.fr. Archives: http://caml.inria.fr
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2001-04-26 23:54 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2001-04-26 23:53 [Caml-list] explain this Genlex behavior Chris Hecker
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox