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- Apr 2024
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fsharpforfunandprofit.com fsharpforfunandprofit.com
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let map oneTrackFunction twoTrackInput = match twoTrackInput with | Success s -> Success (oneTrackFunction s) | Failure f -> Failure f And here it is in use with canonicalizeEmail: let usecase = validate1 >=> validate2 >=> validate3 >> map canonicalizeEmail // normal composition Note that normal composition is now used because map canonicalizeEmail is a fully two-track function and can be connected to the output of the validate3 switch directly. In other words, for one-track functions, >=> switch is exactly the same as >> map. Your choice.
QUESTION
mapcan be defined usingbindandswitch,let map f = bind (switch f)but how to do this with
>=>?...ANSWER
Found a solution, but this is quite stupid:
let map' f result = match result with // The value of `o` is irrelevant, it is only needed // because `>=>` returns a function, but we need // a value and both operands of the input `f` are // provided by the closures | Ok o -> ((fun _ -> result) >=> (switch f)) o | Error e -> Error eNOTE<br /> Call them as:
map ((+) 2) ((Ok 27) : Result<int,string>);; map' ((+) 2) ((Ok 27) : Result<int,string>);;
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