AoC: scanf missing and error referring to --UNDEFINED--

[fridis]

While playing around with dec 20 solution, tried to use different versions of Sequence.scan just to find that there is none that takes a function, only a monoid is allowed.

But passing a function (+) results in an error referring to --UNDEFINED--:

 > $FUZION/bin/fz -e 'say <| (1 :: id).scan (+)'

command line:1:23: error 1: Incompatible types when passing argument in a call
say <| (1 :: id).scan (+)

Actual type for argument #1 'm' does not match expected type.
In call to          : 'list.scan'
expected formal type: 'Monoid i32'
actual type found   : '--UNDEFINED--'
assignable to       : '--UNDEFINED--'
for value assigned  : '(+)'
To solve this, you could change the type of the target 'm' to '--UNDEFINED--' or convert the type of the assigned value to 'Monoid i32'.

one error.