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f#functional-programming
Horst Lemke
Horst Lemke

Reputation: 351

Functional equivalent to if expressions with variable comparison

I have some complex if statement which is not very well readable. it works similar to following example:

let a = 1
let b = 2
let test v = true
if a <> b then a - 1
else
   if (test a) then a + 1
   else a

Is there a better functional solution? I thought of something like

match a with
| b -> ...
| _ -> ...

but this doesn't work, of course, since b becomes a within that statement.

Upvotes: 2

Views: 187

Answers (2)

Mark Seemann
Mark Seemann

Reputation: 233237

There's nothing 'unfunctional' about if..then..else expressions; even Haskell has them ;)

While, as John Palmer's answer shows, you can write

match a with
| foo when foo <> b -> a - 1
| foo when test foo -> a + 1
| _ -> a

you can also write

if a <> b then a - 1
elif test a then a + 1
else a

Personally, in this case I'd prefer the if..then..else syntax, as it's slightly shorter and (IMO) more concise.

Upvotes: 5

John Palmer
John Palmer

Reputation: 25516

This is how it would look with a match

match a with
|foo when foo=b -> ..
|foo when test foo -> ...
|_ -> a

you need to use when

Upvotes: 3

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