Sorry, but Functors are not a means to map over an Array

#functional #javascript #learning

...because they are much more general: Functors lift any ordinary function into numerous structures and effectful contexts.

See how we lift the pure function inc = x => x + 1 in a context that either produces an Array asynchronously or yields nothing at all. All it takes is the composition of these three functions:

const tMap = f => tx =>
  Task((res, rej) => tx.task(x => res(f(x)), rej));

const optMap = f => tx =>
  match(tx, {
    None: _ => None,
    Some: ({some: x}) => Some(f(x))
  });

const arrMap = f => xs =>
  xs.map((x, i) => f(x, i));