[Caml-list] Re: A similar small problem

[Caml-list] Re: A similar small problem

[sebastien FURIC]

Klaus Benecke a écrit :
> 
> Thank you very much for your comments,
> I installed OCAML 3.01 and the mentioned problems disappeared,
> but a similar problem remains:
> 
> let rec inclu_l=fun
>  [] l -> true
>  | (n::ns) l -> mem n l & inclu_l ns l;;
> 
>  File "C:/OTTO/CAMLquellen/XML2002/test.ml", line 3, characters
> 1-2:
> Syntax error
> Can you help me once more?
> Mit freundlichen Gruessen
> Klaus Benecke
> e-mail: benecke@iws.cs.uni-magdeburg.de
> home-page: http://theo.cs.uni-magdeburg.de/benecke.html
 
 "fun patt1 patt2 ... pattn ->" could be view as a macro for:
 "function patt1 -> function patt2 -> ... function pattn ->"
 so your program is not syntactically valid. You have to use "match ...
with" if you want to match against more than one pattern:

 let rec inclu_l ns l = match ns, l with
  | [], _ -> true
  | n :: ns', _ -> mem n l && inclu_l l ns'

 However, since you don't have to match "l" against anything (hence
wildcards), you can simply write:

 let rec inclu_l ns l = match ns with
  | [] -> true
  | n :: ns' -> mem n l && inclu_l l ns'

 Or, (syntactically) better:

 let rec inclu_l l = function
  | [] -> true
  | n :: ns -> mem n l && inclu_l l ns

 by exanching "l" with the matched list (arguments that do not need to
be matched are often placed at first positions).

 Cheers,

 Sebastien.
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