Obscure definition problem

[ivan-kleshnin]

This code is ok, but does not compile

let filterMatrix = function (v: number, m: Array<Array<number>>): Array<number> {
  return chain(filter((c) => c == v), m)
}

let b = [
  [0, 1],
  [1, 0]
]

console.log(filterMatrix(1, b)) // --> [1, 1]

I'm getting this

TSError: ⨯ Unable to compile TypeScript
src/board.ts (11,10): Type '{}[]' is not assignable to type 'number[]'.
  Type '{}' is not assignable to type 'number'.

[ivan-kleshnin]

Error disappears if no currying is present.

// compiles
let filterMatrix = function (v: number, m: Array<Array<number>>): Array<number> {
  return chain((r) => filter((c) => c == v, r), m)
}

Mapping compiles as it should so I guess the problem is with filter definition but I failed to find it

// also compiles
let mapMatrix = function (fn, m: Array<Array<number>>): Array<number> {
  return chain(map((c) => fn(c)), m)
}

[KiaraGrouwstra]

Your hunch was right: the curried filter definition had an issue. Just now it used filter<T>(pred: Pred<T>): <T>(list: List<T>) => T[];, which should have been filter<T>(pred: Pred<T>): (list: List<T>) => T[];.

Note that in the former version the generic was redefined halfway through (no longer the same T!), as a result of which the type variables failed to link up.
Having fixed that, your example type-checks presuming you allow it to find the parameter type for (c) => c == v, using (c: number) => c == v or R.equals(v).

This helped me track down a bunch of related cases of duplicate generics as well. Thank you for reporting this! In fact, this is making me reconsider the 'solution' to #90...

[ivan-kleshnin]

@tycho01 thanks for taking time to fix this!

[KiaraGrouwstra]

You're welcome; thank you for your helpful bug reports. :)