[erlang-questions] Local namespaces in case/try

Richard Carlsson <>
Tue Jul 10 13:03:36 CEST 2012


On 07/10/2012 12:52 PM, Sergei Lebedev wrote:
> Your argument makes sense, but I wonder why list comprehensions don't
> follow this design decision? Of course, from the implementation point
> of view the answer is obvious -- list comprehensions are compiled to
> functions, which indeed have a separate namespace. But for me, as a
> user, it's one more rule to learn; I think scoping rules should be
> consistent, especially if the goal is to keep Erlang semantics as
> simple as possible.

Funs and list comprehensions are indeed exceptions, and they do somewhat 
complicate the language. Not everyone was happy when funs were added, 
for example. I think funs tend to work because they are not so heavily 
used, and you do get warnings about shadowed variables - something that 
I personally thought was stupid to begin with, but eventually I realized 
that taken with Erlang's normal scoping rules, it's best to avoid 
variable shadowing to keep the code readable and maintainable.

When it comes to list comprehensions, I think that they were added a bit 
too quickly without much peer review of the finer details. It is nice to 
be able to have only local scope for variables bound in generators, but 
on the other hand it trips people up sometimes. But list comprehensions 
are well delimited visually and don't usually cause confusion.

    /Richard



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