std.functional.curry isn't flexible enough

[dlangBugzillaToGithub]

bearophile_hugs reported this on 2012-05-24T14:40:11Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=8142

Description

std.functional.curry doesn't work if the first argument (the curried one) is a function. This is a common enough use case:


import std.functional;
auto foo(T)(T function(T x) f, T x) {
    return f(x);
}
int bar(int x) { return x * 2; }
alias curry!(foo, &bar) fooBar;
void main() {}


DMD 2.060alpha gives:

temp.d(6): Error: expression & bar is not a valid template value argument
temp.d(6): Error: template instance std.functional.curry!(foo,& bar) error instantiating

I think D functional-style programming needs a more flexible/uniform currying.


Workaround:

import std.traits: ParameterTypeTuple;
auto foo(alias F)(ParameterTypeTuple!F[0] x) {
    return F(x);
}
int bar(int x) { return x * 2; }
alias foo!bar fooBar;
void main() {
    assert(fooBar(5) == 10);
}


But this is not as flexible. A language that supports functional programming needs to handle functions as first class citizens.