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Newbie problem with cross recursion
f#

Hi,

Waiting to receive "Expert F#" i've ordered, i'm trying to express in F# some functions i have already written both in Haskell and Erlang... So far, so good, except for the case below, where cross recursion is needed.

Consider the following implementation of isEven and isOdd in Haskell (i don't pretend it's the best one, but that the one i want to write in F#).

estPair :: Int -> Bool

estPair 0 = True

estPair n = not (estImpair n)

estImpair :: Int -> Bool

estImpair 1 = True

estImpair n = estPair (n - 1)

I've googelized and found (but that's for CamL) that i could write something like that :

let rec estPair x = if x = 0 then true else ! (estImpair x)

and estImpair x = if x = 0 then false else estPair (x - 1)

but it doesn't compile...

I get:

tp1.fs(58,56): error FS0003: This value is not a function and cannot be applied

where line 58 is the "let" line...

Any clue or pointer ?

.

the ! operator is for reading a ref type.

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let f = ref 2

let g = !x + 3 // access

f := 5 // assign

i think you want:

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let rec estPair x = if x = 0 then true else not (estImpair x) 

and estImpair x = if x = 0 then false else estPair (x - 1)
By on 4/1/2009 6:20 AM ()

the ! operator is for reading a ref type.

Well... I'm not yet on ref types :)

i think you want:

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let rec estPair x = if x = 0 then true else not (estImpair x) 

and estImpair x = if x = 0 then false else estPair (x - 1)

Yep, i've found the same solution... thank you!

By on 4/1/2009 6:48 AM ()

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