Monads/Writer monad: Difference between revisions
Realize in F#
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</lang>
=={{header|F_Sharp|F#}}==
<lang fsharp>
// Monads/Writer monad . Nigel Galloway: July 20th., 2022
type Riter<'n,'g>=Riter of 'n * List<'g>
let bind=function |(n,g)->Riter(n,[g])
let eval=function |Riter(n,g)->(n,g)
let compose f=function |Riter(n,g)->let n,l=eval(f n) in Riter(n,List.append g l)
let initV(n:float)=bind(n,sprintf "Initial Value %f" n)
let sqrt n=bind(sqrt n,"Took square root")
let div2 n=bind(n/2.0,"Divided by 2")
let incr n=bind(n+1.0,"Added 1")
let result,log=eval(initV 5.0|>compose sqrt|>compose incr|>compose div2)
log|>List.iter(printfn "%s")
printfn "Final value = %f" result
</lang>
{{out}}
<pre>
Initial Value 5.000000
Took square root
Added 1
Divided by 2
Final value = 1.618034
</pre>
=={{header|Factor}}==
Factor comes with an implementation of Haskell-style monads in the <code>monads</code> vocabulary.
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