[erlang-questions] Can I do var-assignment in a function?

Roessner, Silvester <>
Wed Jul 23 15:29:39 CEST 2008


Circular Function wrote:
>   extract(Str) ->
>     A = string:tokens(Str," ").
>     lists:sort(A).

I think the comma was just a typo and not the actual question. Am I right?

You want var-assignment because you want to write something like:

	extract(Str) ->
	     A = string:tokens(Str," "),
	     A = lists:sort(A),
	     A = do_something_else(A),
	     A = and_finalize(A).

But that doesn't work. You have to use a new variable each time.

	extract(Str) ->
	     A1 = string:tokens(Str," "),
	     A2 = lists:sort(A1),
	     A3 = do_something_else(A2),
	     A4 = and_finalize(A3).

Or this hard to read version

	extract(Str) ->
	     A = and_finalize(do_something_else(lists:sort(string:tokens(Str," ")))).

This approach of functional languages has at least two big advantages: 

	1. You don't accidentally overwrite variables
	2. You can see all results in the debugger.

And there should be no runtime penalty. Since the processor had to allocate and de-allocate the same amount of memory in each of the 3 cases -even if you don't see this in the code.

mit freundlichen Grüßen / with kind regards
 
Silvester Rößner
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