[erlang-questions] Lists Comprehension issue?

Duan, Xiande xiande.duan@REDACTED
Wed Jan 14 07:08:51 CET 2015

The “L” must be a list of list. Like:

1> L = [[1,2,3],[a,b,c]].
2> [X || L1 <- L, X <- L1].

From: erlang-questions-bounces@REDACTED [mailto:erlang-questions-bounces@REDACTED] On Behalf Of Carlos Suarez Fontalvo
Sent: Wednesday, January 14, 2015 1:06 PM
To: erlang-questions@REDACTED
Subject: [erlang-questions] Lists Comprehension issue?

Hi. I've reading this documentation: http://www.erlang.org/doc/programming_examples/list_comprehensions.html
And it says that
3.5  Simplifications with List Comprehensions

As an example, list comprehensions can be used to simplify some of the functions in lists.erl:

append(L)   ->  [X || L1 <- L, X <- L1].

map(Fun, L) -> [Fun(X) || X <- L].

filter(Pred, L) -> [X || X <- L, Pred(X)].

However when I tried to test this first example "append" doing something simple like this:

73> [X || L1 <- 20, X <- L1].
** exception error: bad generator 20

I got a "exception error" message. Any idea why?. Am I not considering something?

Thanks in advance

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