Given f = fn -> 2 end g = fn -> 2 end How can I match the result of g with f’s ? If I do it like this, it fails because function calls are not allowed in pattern matching. case g.() do f.() -> 1 4 -> 2, 5 -> 3, _ -> 6 end Note: This is dummy version of what I need to do in my project.…

f_result = f.() case g.() do ^f_result -> 1 4 -> 2, 5 -> 3, _ -> 6 end

Given that you can just assign the result of a function call to a variable and match on that it’s always seemed surprising to me that the compiler doesn’t do this for you. Is there a technical reason for this not being supported or is it something that might happen at some point?

[image] opsb: Is there a technical reason for this not being supported or is it something that might happen at some point? Matches are run in linear time, they can’t allow for arbitrary function calling or anything of the sort as they get compiled to a fairly efficient jumplist (sometimes).

a = fast_op() b = long_running_thing() case c do ^a -> 1 ^b -> 2 end Is very explicit that no matching would happen before both calls have returned, whereas the “sugared” version you suggest might hide this fact and a naive reader would assume that long_running_thing() never gets called when cm…

[image] NobbZ: a = fast_op() b = long_running_thing() case c do ^a -> 1 ^b -> 2 end And of course you’d generally want to run this one as this anyway: cond do ^c = fast_op() -> 1 ^c = long_running_thing() -> 2 end ^.^

Doesn’t this crash as soon as fast_op/0s return value isn’t matching cs value? I think its this you mean: cond do c === fast_op() -> 1 c === long_running_thing() -> 2 end

[image] NobbZ: Doesn’t this crash as soon as fast_op/0 s return value isn’t matching c s value? Er, right, my bad, I meant this: cond do match?(^c, fast_op()) -> 1 match?(^c, long_running_thing()) -> 2 end ^.^; Although using == would probably be better in this specific case, since it’…

[image] NobbZ: I think its this you mean: cond do c === fast_op() -> 1 c === long_running_thing() -> 2 end That’s exactly what I was looking for as a replacement for the [image] NobbZ: a = fast_op() b = long_running_thing() case c do ^a -> 1 ^b -> 2 end which keeps getting o…

Elixir Programming Language Forum

Can't use function calls in pattern matching

Questions & Help Questions

kokolegorille July 14, 2019, 2:43am 2

What about this?

case {f.(), g.()} do
  {x, y} -> #whatever
end