Are contraints on function parameters possible? And how do I call the interfaces/functions of type classes?

[philschonholzer]

Is it possible to write the following Haskell code with fp-ts? I want my function to accept any arguments that implement the Monoid type class.

merge :: Monoid m => m -> m -> m
merge m1 m2 = m1 <> m2

How would I would this be written in TS?

const merge = (m1: ???, m2: ???): ??? => {
  return ???.concat(m1, m2);
}

The constraint is one thing, but how do I get my m1 and m2 to be a Monoid and how do I call concat?

Is this even possible? And how?

[xuanduc987]

Yes, it is possible but you will have to pass typeclass instance around.

import { Monoid } from 'fp-ts/Monoid'
import { string } from 'fp-ts'

const merge = <A>(M: Monoid<A>) => (m1: A, m2: A): A => {
  return M.concat(m1, m2)
}

console.log(merge(string.Monoid)("abc", "xyz")) // => abcxyz

[philschonholzer]

Thanks! That makes sense.