Result

map provides a Functor compatible interface for Belt.Result.t. There are 2 laws which a Functor must meet.

1. Identity

   Js.log2("Should be 42", Result.map(x => x, Result.return(42)));

   [@@@ocaml.ppx.context { cookies = [] }]
   open Result
   let _ =
     Js.log2 (("Should be 42")[@reason.raw_literal "Should be 42"])
       (Result.map (fun x  -> x) (Result.return 42))

2. Composition

   let f = x => x + 1;
   let g = x => x + 2;
   let a = Result.map(x => f(g(x)), Result.return(0));
   let b = Result.map(f, Result.map(g, Result.return(0)));
   Js.log2("Should be true", a == b);

   [@@@ocaml.ppx.context { cookies = [] }]
   open Result
   let f x = x + 1
   let g x = x + 2
   let a = Result.map (fun x  -> f (g x)) (Result.return 0)
   let b = Result.map f (Result.map g (Result.return 0))
   let _ =
     Js.log2 (("Should be true")[@reason.raw_literal "Should be true"]) (a = b)

map2 provides the Functor compatible map over 2 results and passes the contents of those results to a function with an arity of 2.

map3 provides the Functor compatible map over 3 results and passes the contents of those results to a function with an arity of 3.

flatMap (chain) provides a Monad compatible interface for Belt.Result.t. There are 2 laws which a Monad must meet.

1. Left identity

   let f = x => Result.return(x + 1);
   let a = 42;
   let x = Result.flatMap(f, Result.return(a));
   Js.log2("Should be true", x == f(a));

   [@@@ocaml.ppx.context { cookies = [] }]
   open Result
   let f x = Result.return (x + 1)
   let a = 42
   let x = Result.flatMap f (Result.return a)
   let _ =
     Js.log2 (("Should be true")[@reason.raw_literal "Should be true"])
       (x = (f a))

2. Right identity

   let a = Result.return(42);
   let x = Result.flatMap(Result.return, a);
   Js.log2("Should be true", a == x);

   [@@@ocaml.ppx.context { cookies = [] }]
   open Result
   let a = Result.return 42
   let x = Result.flatMap Result.return a
   let _ =
     Js.log2 (("Should be true")[@reason.raw_literal "Should be true"]) (a = x)

flatMap2 provides the Monad compatible flatMap over 2 results and passes the contents of those results to a function with an arity of 2.

flatMap3 provides the Monad compatible flatMap over 3 results and passes the contents of those results to a function with an arity of 3.

This operation is the pure Applicative operation for lifting a value into the Result context.

let r = Result.return(42);

[@@@ocaml.ppx.context { cookies = [] }]
open Result
let r = Result.return 42

This operation is the constructor to lift a value into the Result context as an Error.

let e = Result.error("bad things");

[@@@ocaml.ppx.context { cookies = [] }]
open Result
let e = Result.error (("bad things")[@reason.raw_literal "bad things"])

Applicative apply operation. This implements the Applicative specification

1. Identity

   let f = Result.return(x => x);
   let a = Result.return(2);
   let b = Result.ap(a, f);
   Js.log2("Should be true", a == b);

   [@@@ocaml.ppx.context { cookies = [] }]
   open Result
   let f = Result.return (fun x  -> x)
   let a = Result.return 2
   let b = Result.ap a f
   let _ =
     Js.log2 (("Should be true")[@reason.raw_literal "Should be true"]) (a = b)

2. Homomorphism

   let f = x => x + 1;
   let x = 2;
   let a = Result.ap(Result.return(x), Result.return(f));
   let b = Result.return(f(x));
   Js.log2("Should be true", a == b);

   [@@@ocaml.ppx.context { cookies = [] }]
   open Result
   let f x = x + 1
   let x = 2
   let a = Result.ap (Result.return x) (Result.return f)
   let b = Result.return (f x)
   let _ =
     Js.log2 (("Should be true")[@reason.raw_literal "Should be true"]) (a = b)

3. Interchange

   let u = x => x + 1;
   let y = 1;
   let a = Result.ap(Result.return(y), Result.return(u));
   let b = Result.ap(Result.return(u), Result.return(f => f(y)));
   Js.log2("Should be true", a == b);

   [@@@ocaml.ppx.context { cookies = [] }]
   open Result
   let u x = x + 1
   let y = 1
   let a = Result.ap (Result.return y) (Result.return u)
   let b = Result.ap (Result.return u) (Result.return (fun f  -> f y))
   let _ =
     Js.log2 (("Should be true")[@reason.raw_literal "Should be true"]) (a = b)

bimap provides a Bifunctor compatible interface for Belt.Result.t. There are 2 laws which a Bifunctor must meet.

1. Identity

   let a = Result.return(42);
   let b = Result.error("boom!");
   let a1 = Result.bimap(a => a, b => b, a);
   let b1 = Result.bimap(a => a, b => b, b);
   Js.log3("Both should be true", a == a1, b == b1);

   [@@@ocaml.ppx.context { cookies = [] }]
   open Result
   let a = Result.return 42
   let b = Result.error (("boom!")[@reason.raw_literal "boom!"])
   let a1 = Result.bimap (fun a  -> a) (fun b  -> b) a
   let b1 = Result.bimap (fun a  -> a) (fun b  -> b) b
   let _ =
     Js.log3
       (("Both should be true")[@reason.raw_literal "Both should be true"])
       (a = a1) (b = b1)

2. Composition

   let f = x => x + 1;
   let g = x => x + 2;
   let h = x => x + 3;
   let i = x => x + 4;
   let a = 42;
   let b = 24;
   let ok1 = Result.bimap(a => f(g(a)), b => h(i(b)), Result.return(a));
   let ok2 = Result.bimap(g, i, Result.bimap(f, h, Result.return(a)));
   let err1 = Result.bimap(a => f(g(a)), b => h(i(b)), Result.error(b));
   let err2 = Result.bimap(g, i, Result.bimap(f, h, Result.error(b)));
   Js.log3("Both should be true", ok1 == ok2, err1 == err2);

   [@@@ocaml.ppx.context { cookies = [] }]
   open Result
   let f x = x + 1
   let g x = x + 2
   let h x = x + 3
   let i x = x + 4
   let a = 42
   let b = 24
   let ok1 =
     Result.bimap (fun a  -> f (g a)) (fun b  -> h (i b)) (Result.return a)
   let ok2 = Result.bimap g i (Result.bimap f h (Result.return a))
   let err1 =
     Result.bimap (fun a  -> f (g a)) (fun b  -> h (i b)) (Result.error b)
   let err2 = Result.bimap g i (Result.bimap f h (Result.error b))
   let _ =
     Js.log3
       (("Both should be true")[@reason.raw_literal "Both should be true"])
       (ok1 = ok2) (err1 = err2)

Returns a Belt.Option.Some('a) if the source is an Ok('a), or a Belt.Option.None if the source is an Error('b).

Given a Belt.Option.t('a) and a function unit => 'b return an Ok('a) if the given Belt.Option.t('a) is a Belt.Option.Some('a), or an Error('b) if the input is a Belt.Option.None.