Suggestion for abstract casts for functions

[kevinresol]

package;

class Main {
	static function main() {
		var e:Expr = function(e) return 1; // doesn't compile
	}
}

abstract Expr(String) from String to String {
	@:from
	public static function ofInt(i:Int):Expr
		return Std.string(i);
	@:from
	public static function ofFunc(f:Expr->Expr)
		return f('bar');
}

I wish it would work somehow like the below:
Compiler sees it is trying to cast Unknown->Int to Expr. While the compiler search down the @:from list for compatible casts, if it sees 1-argument function cast with non-identical type signature, don't skip right away but try to cast each of the arguments and return type accordingly
i.e. Unknown to Expr & Int to Expr respectively. If all the casts succeed, use that cast.

[Simn]

I never really looked at this issue and now that I am looking at it I don't understand it. Sounds like some black magic, so whatever you want to do here would require a haxe-evolution.