[Javascript] Functor law

Posted 2020-08-08

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Functor laws:

1. Identity:

map(id) == id

2. Composition:

compose(map(f), map(g)) == map(compose(f,g))

compose(
 map(toUpper),
 map(reverse),
 toArray   
)("bingo");


compose(
 map(
   compose(toUpper reverse),
   toArray
 )
)("bingo")

Natural Transformations:

"Takes one functor to another without knowing anything about the value".

maybeToArray(Maybe(2)) // [2]
maybeToArray(Maybe(null)) // []

compose(nt, map(f)) == compose(map(f), nt)

compose(maybeToArray, map(add(1)))(Maybe(5)) //[6]

compose(map(add(1)), maybeToArray)(Maybe(5)) // [6]

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