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digitalmars.D.learn - Patterns for functions in template parameters

reply "Max Samukha" <maxsamukha gmail.com> writes:
If I remember correctly, at some point a syntax was introduced 
for pattern-matching functions passed to templates. Something 
like:

template Foo(B(A) foo, A, B)
{
}

alias f = Foo!((int x) => x % 2 == 0);

That would instantiate Foo with B == bool, A == int and foo bound 
to the lambda.

The compiler has rejected all syntax variations I have tried and 
the specs is not helpful. Does anybody know if the feature exists 
and what is the syntax exactly?
Oct 23 2014
parent reply "Kagamin" <spam here.lot> writes:
Maybe, argument deduction?

template Foo(T: T[U], U)
{
     ...
}

Foo!(int[long])  // instantiates Foo with T set to int, U set to 
long
Oct 23 2014
parent reply "Max Samukha" <maxsamukha gmail.com> writes:
On Thursday, 23 October 2014 at 11:25:01 UTC, Kagamin wrote:

 Maybe, argument deduction?

 template Foo(T: T[U], U)
 {
     ...
 }

 Foo!(int[long])  // instantiates Foo with T set to int, U set 
 to long


Yes, but for a value template parameter.

template Foo(int[long] a);
{
}
Foo!([1: 2]); // ok, this passes.


Now I'd like to loosen the template so it accepts AAs of any type:

template Foo(T[U] a /* forall T, U */)
{
}


And then unary functions of any type:

template Foo(T a(U) /* forall T, U */)
{
}


In other words, to move the run-time parameter below to the 
template parameter list:

void foo(T, U)(T delegate(U) a)
{
}


Or in other other words (for any "callables"):

template Foo(alias a) if (isCallable!a && ParameterTypes!a.length 
== 1)
{
     alias T = ReturnType!a;
     alias U = ParameterTypes!a[0];
}


I vaguely remember some syntax tweaks were introduced, presumably 
for that effect. Trying to find out what they were exactly. I 
might have dreamt it as well.
Oct 23 2014
next sibling parent reply "Kagamin" <spam here.lot> writes:
maybe
template Foo(T a, T: T[U], U)
Oct 24 2014
parent "Max Samukha" <maxsamukha gmail.com> writes:
On Friday, 24 October 2014 at 08:53:05 UTC, Kagamin wrote:

 maybe
 template Foo(T a, T: T[U], U)


No luck. Error: undefined identifier T
Oct 24 2014
prev sibling next sibling parent reply ketmar via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
On Thu, 23 Oct 2014 18:28:04 +0000
Max Samukha via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
wrote:

um-hm... maybe this:

  void Foo(T, U) (T delegate (U) a) {
    // here T is bool, U is int for the following sample
    import std.stdio;
    writeln(a(3));
  }

  Foo((int x) =3D> x%2 =3D=3D 0);
Oct 24 2014
parent reply "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> writes:
On Friday, 24 October 2014 at 14:06:08 UTC, ketmar via 
Digitalmars-d-learn wrote:

 On Thu, 23 Oct 2014 18:28:04 +0000
 Max Samukha via Digitalmars-d-learn 
 <digitalmars-d-learn puremagic.com>
 wrote:

 um-hm... maybe this:

   void Foo(T, U) (T delegate (U) a) {
     // here T is bool, U is int for the following sample
     import std.stdio;
     writeln(a(3));
   }

   Foo((int x) => x%2 == 0);


I thought the same thing, but it doesn't compile with DMD from 
Git:

test.d(7): Error: function declaration without return type. (Note 
that constructors are always named 'this')
test.d(7): Error: found '=>' when expecting ')'
test.d(7): Error: no identifier for declarator Foo(int x)
test.d(7): Error: semicolon expected following function 
declaration
test.d(7): Error: no identifier for declarator x
test.d(7): Error: Declaration expected, not '%'
Oct 24 2014
parent reply ketmar via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
On Fri, 24 Oct 2014 16:00:41 +0000
via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> wrote:


 On Friday, 24 October 2014 at 14:06:08 UTC, ketmar via=20
 Digitalmars-d-learn wrote:

 On Thu, 23 Oct 2014 18:28:04 +0000
 Max Samukha via Digitalmars-d-learn=20
 <digitalmars-d-learn puremagic.com>
 wrote:

 um-hm... maybe this:

   void Foo(T, U) (T delegate (U) a) {
     // here T is bool, U is int for the following sample
     import std.stdio;
     writeln(a(3));
   }

   Foo((int x) =3D> x%2 =3D=3D 0);


=20
 I thought the same thing, but it doesn't compile with DMD from=20
 Git:


Foo is a function, not declaration. put in in main(), for example:

  void main () { Foo((int x) =3D> x%2 =3D=3D 0); }
Oct 24 2014
parent "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> writes:
On Friday, 24 October 2014 at 16:12:48 UTC, ketmar via 
Digitalmars-d-learn wrote:

 On Fri, 24 Oct 2014 16:00:41 +0000
 via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> 
 wrote:


 On Friday, 24 October 2014 at 14:06:08 UTC, ketmar via 
 Digitalmars-d-learn wrote:

 On Thu, 23 Oct 2014 18:28:04 +0000
 Max Samukha via Digitalmars-d-learn 
 <digitalmars-d-learn puremagic.com>
 wrote:

 um-hm... maybe this:

   void Foo(T, U) (T delegate (U) a) {
     // here T is bool, U is int for the following sample
     import std.stdio;
     writeln(a(3));
   }

   Foo((int x) => x%2 == 0);


 
 I thought the same thing, but it doesn't compile with DMD from 
 Git:


 Foo is a function, not declaration. put in in main(), for 
 example:

   void main () { Foo((int x) => x%2 == 0); }


Now I'm feeling really stupid :-P
Oct 24 2014
prev sibling parent reply ketmar via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
On Fri, 24 Oct 2014 17:05:57 +0300
ketmar via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
wrote:


 On Thu, 23 Oct 2014 18:28:04 +0000
 Max Samukha via Digitalmars-d-learn
 <digitalmars-d-learn puremagic.com> wrote:
=20
 um-hm... maybe this:
=20
   void Foo(T, U) (T delegate (U) a) {
     // here T is bool, U is int for the following sample
     import std.stdio;
     writeln(a(3));
   }
=20
   Foo((int x) =3D> x%2 =3D=3D 0);


sorry if this is not what you mean, template magic sometimes scares me
and i'm loosing my mind. ;-)
Oct 24 2014
parent reply "Max Samukha" <maxsamukha gmail.com> writes:
On Friday, 24 October 2014 at 14:13:10 UTC, ketmar via 
Digitalmars-d-learn wrote:


 sorry if this is not what you mean, template magic sometimes 
 scares me
 and i'm loosing my mind. ;-)


What I meant was your example with the delegate parameter moved 
to the template list:

template Foo(T delegate(U) a, T, U) {}
Foo!((int x) => true); // T == bool, U == int


Or generalized to functions (and maybe "functors" in the 
unfortunate C++ sense):

template Foo(T(U) a, T, U) {}


Apparently, D doesn't allow type variables in value parameters at 
all.
Oct 24 2014
parent "Max Samukha" <maxsamukha gmail.com> writes:
On Friday, 24 October 2014 at 17:08:00 UTC, Max Samukha wrote:


 Apparently, D doesn't allow type variables in value parameters 
 at all.


Nor does it allow passing delegates to value parameters, only 
alias parameters.
Oct 24 2014