Can pattern variables be globally bound?
Sat Mar 25 15:15:18 CET 2006
You are correct. Essentially when X != 0, you are trying to
essentially say "b IFF X*10 == X". Which is generally not true :-)
So you get a case clause exception.
The subject line is a little misleading, since variables can only
exist in the context of a single function "scope" - with lexical
scoping rules of course for fun()s.
"Global" variables can be accomplished with the process dictionary or
ets or mnesia tables. There are other techniques, like using a
gen_server to maintain state across requests (using recursion/tail
On 3/25/06, Roger Price <> wrote:
> The following program:
> -module(test) . % 1
> -export([test/1]) . % 2
> test (X) -> % 3
> case X*10 % 4
> of 0 -> a % 5
> ; X -> b % 6
> end . % 7
> compiles with no warnings, and provides the following output:
> Eshell V5.4.9 (abort with ^G)
> 1> test:test(0) .
> 2> test:test(1) .
> =ERROR REPORT==== 25-Mar-2006::14:20:45 ===
> Error in process <0.31.0> with exit value:
> My understanding of the error message is that the pattern variable X on
> line 6 is already bound to the value 1, and therefore no match is possible
> for value 10. Is this correct?
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