[Haskell-cafe] mdo with multiple values

Joachim Breitner mail at joachim-breitner.de
Thu Jan 16 10:49:09 UTC 2014


Am Donnerstag, den 16.01.2014, 11:34 +0100 schrieb Heinrich Apfelmus:
> Fortunately, we do known the spine of `offsets` in advance: it has the 
> same spine as `byteStrings`. The solution is to make that explicit in 
> the code, by using a lazy `zip`:
>       ...
>       mapM_ putWord32 (offsets `spine` byteStrings)
>       ...
>     where
>     spine :: [a] -> [void] -> [a]
>     spine ~[]     []     = []
>     spine ~(x:xs) (y:ys) = x : tag xs ys
> This code takes the spine of `byteStrings` and fills it with values from 
> `offsets`.

I thought about something in that direction; but thanks for working it

What I do not like about this solution is that it is not safe: As a
programmer I have two make sure that offsets and byteStrings actually
have the same length.


Joachim Breitner
  e-Mail: mail at joachim-breitner.de
  Homepage: http://www.joachim-breitner.de
  Jabber-ID: nomeata at joachim-breitner.de

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