Generic function does not match generic param to `void`

[iacore]

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The compiler cannot match procedure types like proc (_: T): R.

See https://nim-lang.org/docs/manual.html#overload-resolution for the definition of "generic match"

Example

type
    Callback*[S,R] = proc(_:S): R
    State = object

proc foo*[S,R](action: Callback[S,R]) =
  discard

proc noop(state: State): void = discard

foo(noop) # fail
foo[State,void](noop) # success

Current Output

Error: type mismatch: got <proc (state: State){.noSideEffect, gcsafe, locks: 0.}>
but expected one of:
proc foo[S, R](action: Callback[S, R])
  first type mismatch at position: 1
  required type for action: Callback[foo.S, foo.R]
  but expression 'noop' is of type: proc (state: State){.noSideEffect, gcsafe, locks: 0.}

expression: foo(noop)

Expected Output

No compiler error

Possible Solution

idk

Additional Information

I was modifying someone's state machine library when I encountered this problem.

Offending part: addTransition does not match without explicit type parameters

import tables, options

type
  Callback*[S,R] = proc(_:S): R
  StateEvent*[S,E] = tuple[state: S, event: E]
  Transition*[S,R] = tuple[nexState: S, action: Callback[S,R]]

  Machine*[S,E,R] =  object
    state*: S
    transitions*: Table[StateEvent[S,E], Transition[S,R]]

proc addTransition*[S,E,R](m: var Machine[S,E,R], state: S, event: E, nextState: S, action: Callback[S,R]) =
  m.transitions[(state, event)] = (nextState, action)

Nim version

> nim -v
Nim Compiler Version 1.6.2 [Linux: amd64]
Compiled at 2021-12-17
Copyright (c) 2006-2021 by Andreas Rumpf

git hash: 9084d9bc02bcd983b81a4c76a05f27b9ce2707dd
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