Accumulate Err on Alt for Result type

[evilsoft]

Best Laid Plans

After messing about with Alt and trying to come up with helpers for Alternative and Alt, I was really sad that Result did not accumulate Err like it does with ap. It would be very useful and does not seem to break any laws.

So that is what this is. Now if you use a Semigroup for your Err and use alt it will concat your Errs. If you do not use a Semigroup, then alt behaves in a manner that works like Either.alt, in which it return the first Ok, but the last Err. Like so:

const withSemi =
  Err([ 3 ])
    .alt(Err([ 13 ]))
    .alt(Err([ 42 ]))

const noSemi =
  Err(3)
    .alt(Err(13))
    .alt(Err(42))

withSemi
// > Err [ 3, 13, 42 ]

withSemi
  .alt(Ok('yep'))
// > Ok 'yep'

noSemi
// > Err 42

noSemi
  .alt(Ok('yep'))
// > Ok 'yep'

[coveralls]

Coverage remained the same at 100.0% when pulling 0d967c9 on result-alt-accum into 5de3309 on master.

[evilsoft]