[erlang-questions] style question - best way to test multiple non-guard conditions sequentially
Fri Jun 21 10:21:12 CEST 2013
What we currently have:
qual -> pat '<-' expr.
qual -> bin_pat '<=' expr.
qual -> expr.
I would keep it as is but compile every filter as an expression and the following grammar rule:
expr -> 'when' guard 'end'.
And then I would also add two generators which do not skip elements but crash instead:
qual -> pat '<:-' expr.
qual -> bin_pat '<:=' expr.
I do like the different direction you took though. Allowing only guards mean matches can be handled differently, thus one could write X = foo() instead of begin X = foo(), true end.
Le 21 juin 2013 à 03:34, Richard A. O'Keefe a écrit :
> On 21/06/2013, at 12:35 PM, Anthony Ramine wrote:
>> Guard semantics are not mentioned in the documentation about comprehension filters though.
> Fair enough. And I'm not the least little bit happy about the fact
> that comprehension filters aren't guards.
> I would have expected
> '[' <expr> '||' <stuff> ']'
> <stuff> ::= <stuff> ',' <stuff>
> | <pattern> '<-' <expression>
> | <pattern> '=' <expression>
> | <possibly parenthesised guard>
> We can tolerate a thing being one way (X < Y is only a guard, and if X or Y
> raises an exception, it just fails) or all the other way (guards and
> expressions are identical), but a mixture is bound to confuse.
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