[erlang-questions] Question about lists:filter

Bengt Kleberg <>
Wed Aug 28 14:01:42 CEST 2013


Greetings,

isPal is an atom. If you want to make it into a fun you have to write:
fun isPal/1


bengt

On Wed, 2013-08-28 at 14:54 +0300, Nadav Chernin wrote:
> Hi, all
> 
> 
> I'm learning Erlang with Project Euler.
> 
> 
> This is my solution for problem 4.
> 
> 
> 
> 
> -module(euler).
> -export([problem4/0]).
> 
> 
> cand()->[X*Y||X<-lists:seq(100,999),Y<-lists:seq(100,999)].
> isPal(X)->integer_to_list(X)==lists:reverse(integer_to_list(X)).
> problem4()->lists:max(lists:filter(fun(A)->isPal(A) end,cand())).
> 
> 
> Before it, my code was:
> 
> 
> -module(euler).
> -export([problem4/0]).
> 
> 
> cand()->[X*Y||X<-lists:seq(100,999),Y<-lists:seq(100,999)].
> isPal(X)->integer_to_list(X)==lists:reverse(integer_to_list(X)).
> problem4()->lists:max(lists:filter(isPal,cand())).
> 
> 
> Difference from my final solution - using isPal instead
> fun(A)->isPal(A) end
> 
> 
> But exception occured during execution:
> 
> 
> exception error: no function clause matching 
>                     lists:filter(isPal,
> 
>  [10000,10100,10200,10300,10400,10500,10600,
> 
> 10700,10800,10900,11000,11100,11200,11300,
> 
> 11400,11500,11600,11700,11800,11900,12000,
> 
> 12100,12200,12300,12400,12500,12600|...])
> 
> 
> Please, explain me why i can't use function as is, without using
> lambda function.
> I come to Erlang from Haskell, and there i can do this,
> 
> 
> Thanks, Nadav
> 
> 
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