Facilitate Creation of Function Pointers / Lambdas?

[SebastienGllmt]

The following is the smallest example of a lambda I could come up with (calling foo() and calling baz() will have the same result)

contract "lambdaTest" {

// this will be our lambda
define public @foo() {
entry:
  ret 1234
}

// In a real world setting, this function would return a different lambda based on some condition
define public @bar(){
entry:
  %this = call @iele.address()
  %f = calladdress @foo at %this
  ret %f
}

// fetch which lambda to use from bar and then call it
define public @baz() {
entry:
  %f = call @bar()

  %this = call @iele.address()
  %gas = call @iele.gas()
  %status, %result = call %f at %this () send 0, gaslimit %gas
  ret %result
}

define @init() {
entry:
  ret void
}

}

Unfortunately this is not very pretty because

1) Calladdress requires an "at" instead of implicitly using @iele.address() 1) You cannot use call on a register. You must use call at

I don't know why these restrictions exist.

Anyways this is a cool feature and it's much prettier than what you have to do in Solidity which involves mangling byte arrays 👍

[dwightguth]

It's definitely supposed to be possible to do:

call %ptr()

I don't have time to investigate this immediately, but I will look into it sometime in the next couple days. In the meantime, if you want to help, can you tell me what went wrong when you tried to do a local call on a function pointer?

[SebastienGllmt]

I just tried it out and you are right. I must have made a typo or something.

I guess the only consideration now is do we want to make calladdress apply to @iele.address() by default.

[dwightguth]

Probably the simplest solution is to make %foo = calladdress @bar assemble into

%this = call @iele.address()
%foo = calladdress @bar at %this

This would not require a change to the VM and is consistent with the other types of syntactic sugar the assembler offers.