Failre to infer type parameters results in error messaga showing type `**error**`

[fridis]

This code

apply(A type,
      a A,
      f _ : A->String)
=>
  f.call a

say <| apply _ _ 99 x->"$x*2={x*2}"

produces this message

 > ./build/bin/fz ../work/webserver/content/tutorial/examples/type_parameter_example6.fz

/home/fridi/fuzion/fuzion/../work/webserver/content/tutorial/examples/type_parameter_example6.fz:7:21: error 1: Incompatible types when passing argument in a call
say <| apply _ _ 99 x->"$x*2={x*2}"

Actual type for argument #2 'f' does not match expected type.
In call to          : 'apply'
expected formal type: 'Unary String A'
actual type found   : '**error**'
assignable to       : '**error**'
for value assigned  : 'x->"$x*2={x*2}"'
To solve this, you could change the type of the target 'f' to '**error**' or convert the type of the assigned value to 'Unary String A'.

one error.

It should be possible to infer that A must be i32 and then see that the lambda actually is assignable to i32->String.