Nim - Function type of int has to be discarded

Question

I am new to Nim, and wrote this simple code for fun:

var x: int = 3
var y: int = 4
if true:
    y = 7

else:
    x = 7

proc hello(xx: int, yy: int, ): int =
    return xx + yy

hello(x, y)

The code seems fine (I checked with the Nim manuals), but it gives this weird error:

c:\Users\Xilpex\Desktop\Nim_tests\testrig.nim(12, 6) Error: expression 'hello(x, y)' is of type 'int' and has to be discarded

Why am I getting this error? Is there something I can do to fix it?

Answer 1

You are getting an error because procs declared to return values are meant to use that value somewhere, so the compiler reminds you that you are forgetting the result of the call. If some times you want the result, and others you want to ignore it, instead of creating a temporal variable you can use the discard statement or declare the proc as {.discardable.}.