Stream parsing - caml light vs. ocaml

Stream parsing - caml light vs. ocaml

[Norman Davis]

Hello,

I am reading "Functional programming using Caml Light" by Michel Mauny, chapter
10 on Streams and Parsers. The "spaces" function (used to remove the next
continuous segment of whitespace) shown there is : 

# let rec spaces = function 
#   [< '' '|'\t'|'\n'; spaces _ >] -> ()
#|  [< >] -> ();;

I tried converting it to Objective Caml :

# let rec spaces = parser
  [< '' '|'\t'|'\n'; spaces >] -> ()
  | [< >] -> ();;
val spaces : char Stream.t -> unit = <fun>
# let s = Stream.of_string "  ;";;
val s : char Stream.t = <abstr>
# spaces s;;
- : unit = ()
# Stream.next s;;
- : char = ' '
# Stream.next s;;
- : char = ';'

The stream s had two space characters followed by a semicolon.
After "spaces s", I expected "Stream.next s" to return
a semicolon.  What is the correct way to write "spaces" so that it removes all
whitespace from the front of the stream, not just a single whitespace
character.

Thanks.

Norman Davis
ndavis@ti.com

Re: Stream parsing - caml light vs. ocaml

[Toby Moth]

option 1:
let rec spaces = parser  
    [< '' '|'\t'|'\n'; rest >] -> spaces rest
  | [< >] -> ()

option 2:
let rec spaces = parser  
    [< '' '|'\t'|'\n'; _ = spaces >] -> ()
  | [< >] -> ()

which may be what you were thinking of