[Haskell-cafe] How lazy can "peek" be?

[Bayley, Alistair]

> From: Juan Carlos Arevalo Baeza 
>
> If I don't want to pay for that cost, then I have 
> to convert the code as in:
> 
> func p =
>     b <- peekByteOff p 4
>     case b of
>         B1 -> doSomething
>         B2 -> do { a <- peekByteOff p 0; doSomethingElse a }
>         B3 -> do { a <- peekByteOff p 0; doAnotherThing a }
> 
>    Repetition, repetition, repetition. This does get tedious.


Would this work?

> func p = do
>     let get_a = peekByteOff p 0
>     b <- peekByteOff p 4
>     case b of
>         B1 -> doSomething
>         B2 -> do a <- get_a; doSomethingElse a
>         B3 -> do a <- get_a; doAnotherThing a

Or, with marginally less duplication:

>         B2 -> get_a >>= doSomethingElse
>         B3 -> get_a >>= doAnotherThing


Alistair.

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