[erlang-questions] Lists Comprehension issue?

[Carlos Suarez Fontalvo]

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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