[Issue 11403] New: functions in std.algo can't be used as pred

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=11403

           Summary: functions in std.algo can't be used as pred
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: rejects-valid
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody at puremagic.com
        ReportedBy: monarchdodra at gmail.com


--- Comment #0 from monarchdodra at gmail.com 2013-10-31 12:55:31 PDT ---
There are a ton of functions in std.algorithm that can be customized with a
predicate. At ton of them can also be used as predicates themselves. Here is a
cool example:

assert(equal!equal([[1, 2], [3, 4]], iota(1, 5).chunks(2)));

The problem with this piece of code is that:
The inner "equal" only works because it itself doesn't have a predicate.
The outer "equal" works because it takes arguments.

However, neither of this works:
alias fun = equal!equal; //Nope
equal!(equal!equal))(3Dmatrix1, 3Dmatrix2); //Nope

It is *not* possible to declare an algorithm function with a predicate, unless
you also specify the argument types. Long story short, they are not eagerly
specialize-able.

"equal" (I think) is the most obvious offender, but so are any/all:
import std.ascii : isWhite;
assert( all!(any!isWhite)(["a a", "b b"])); //Nope
assert(!any!(all!isWhite)(["a a", "b b"])); //Nope

Any function that takes a pred (+an argument) and returns a bool is faulty.
Here is a (probably incomplete) list:
-equal
-canFind
-any
-all
-cmp

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