On Monday, 25 February 2019 at 06:51:20 UTC, Yevano wrote:
I am writing a domain specific language of sorts in D for the
lambda calculus. One of my requirements is that I should be
able to generate expressions like this:
new Abstraction(v1, M)
like this:
L!(x => M)
It is common to want to write things like
L!(x => L!(y => M))
but it is much nicer to write that like
L!((x, y) => M)
So, I have created a templated function for this.
Abstraction L(alias f)() {
static if(__traits(compiles, f(null))) {
auto v1 = new Variable;
return new Abstraction(v1, f(v1));
} else static if(__traits(compiles, f(null, null))) {
auto v1 = new Variable;
auto v2 = new Variable;
return new Abstraction(v1, new Abstraction(v2, f(v1,
v2)));
} else static if(__traits(compiles, f(null, null, null))) {
auto v1 = new Variable;
auto v2 = new Variable;
auto v3 = new Variable;
return new Abstraction(v1, new Abstraction(v2, new
Abstraction(v3, f(v1, v2, v3))));
}
}
This only works for at most 3 parameter delegates. If I want to
add more, I have to linearly add more static ifs in the obvious
way. However, I believe I can make this function scalable using
string mixins and other magic. Any insight into this is much
appreciated.
import std.traits;
Abstraction L(alias f)() {
alias Args = Parameters!f;
Args v;
foreach(i; 0 .. v.length) v[i] = new Variable;
auto _f = f(v);
auto abstraction = new Abstraction(v[$-1],_f);
foreach_reverse(e; v[ 0 .. $-2])
abstraction = new Abstraction( e, abstraction);
return abstraction;
}
