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I was pretty puzzled by the method name "map" in the examples. Why would you call it "map" when there are no arrays or lists involved?

RyEgswuCsn 5y ago
Because of the mathematical "map" [0] perhaps? [0]: https://en.wikipedia.org/wiki/Map_(mathematics) https://en.wikipedia.org/wiki/Map_(mathematics)
cheriot 5y ago
Are you thinking about Maybe.map in particular? It's the same name because it does the same thing: run this function on the value inside if there is one. It's a Functor :)
dragonwriter 5y ago
A Maybe is effectively isomorphic to an immutable list whose cardinality can only be zero or one.
CodeAndCuffs 5y ago
x.map(f) doesnt mean "apply function f to each element in this list that we called x" x.map(f) means "apply the function f to the value within x, where x is a container of some sort" [].map(f) would do nothing, because there is nothing to pull out. ['adam', 'bill'].map(f) takes 'adam' out of the array, applies f to it, and puts it back in the array, then does the same with 'bill'. Just(5).map(f) takes 5 out of the Maybe, applies f to it, and puts it back in nothing.map(f) returns nothing. So we can map functions to values in Arrays, map functions to values in Maybes and even map functions to values in Eithers. Each time the function doesnt care that the value is in a Maybe or an Array or an Either.
bobbylarrybobby 5y ago
The only requirement for something to be mappable is that it be iterable
growlfrench 5y ago
Brian Lonsdorf has a fun course where he explains these things: https://egghead.io/courses/professor-frisby-introduces-composable-functional-javascript https://egghead.io/courses/professor-frisby-introduces-compo...
r-zip 5y ago
Because the Result and Maybe types in the examples are functors: https://en.wikipedia.org/wiki/Functor_(functional_programming) https://en.wikipedia.org/wiki/Functor_(functional_programmin...

RyEgswuCsn 5y ago

Because of the mathematical "map" [0] perhaps? [0]: https://en.wikipedia.org/wiki/Map_(mathematics) https://en.wikipedia.org/wiki/Map_(mathematics)

cheriot 5y ago

Are you thinking about Maybe.map in particular? It's the same name because it does the same thing: run this function on the value inside if there is one. It's a Functor :)

dragonwriter 5y ago

A Maybe is effectively isomorphic to an immutable list whose cardinality can only be zero or one.

CodeAndCuffs 5y ago

x.map(f) doesnt mean "apply function f to each element in this list that we called x" x.map(f) means "apply the function f to the value within x, where x is a container of some sort" [].map(f) would do nothing, because there is nothing to pull out. ['adam', 'bill'].map(f) takes 'adam' out of the array, applies f to it, and puts it back in the array, then does the same with 'bill'. Just(5).map(f) takes 5 out of the Maybe, applies f to it, and puts it back in nothing.map(f) returns nothing. So we can map functions to values in Arrays, map functions to values in Maybes and even map functions to values in Eithers. Each time the function doesnt care that the value is in a Maybe or an Array or an Either.

bobbylarrybobby 5y ago

The only requirement for something to be mappable is that it be iterable

growlfrench 5y ago

Brian Lonsdorf has a fun course where he explains these things: https://egghead.io/courses/professor-frisby-introduces-composable-functional-javascript https://egghead.io/courses/professor-frisby-introduces-compo...

r-zip 5y ago

Because the Result and Maybe types in the examples are functors: https://en.wikipedia.org/wiki/Functor_(functional_programming) https://en.wikipedia.org/wiki/Functor_(functional_programmin...