[Haskell-beginners] help with IO guards

[Julian Birch]

Here's how I would do it:

Write two functions. One (f) takes the int and gets the IO record. One
(g) takes a (non-IO) record and returns the string. Now you can use a bind
(=<<) to combine the two.

Once you've got that working, you can move the bits into the where clause
of your original function.

Hope this helps.

J

On Thursday, January 15, 2015, Miro Karpis <miroslav.karpis at gmail.com>
wrote:

> Hi,
>
> please is there a way to have guards with 'where' that communicates with
> IO? Or is there some other more elegant way? I can do this with classic
> if/else,...but I just find it nicer with guards.
>
>
> I have something like this (just an example):
>
>
> f :: Int -> IO String
> f x
>     | null dbOutput = return "no db record"
>     | otherwise = return "we got some db records"
>     where dbOutput = getDBRecord x
>
>
> getDBRecord :: Int -> IO [Int]
> getDBRecord recordId = do
>     putStrLn $ "checking dbRecord" ++ show recordId
>     --getting data from DB
>     return [1,2]
>
>
> problem is that db dbOutput is IO and the guard check does not like it:
>
> Couldn't match expected type ‘[a0]’ with actual type ‘IO [Int]’
>     In the first argument of ‘null’, namely ‘dbOutput’
>     In the expression: null dbOutput
>
>
>
> Cheers,
> Miro
>


-- 
Sent from an iPhone, please excuse brevity and typos.
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