using ghc with make

Simon Marlow simonmarhaskell at
Fri Apr 21 04:22:00 EDT 2006

Bulat Ziganshin wrote:

> Thursday, April 20, 2006, 11:54:59 AM, you wrote:
>>lazyGet can only be used to read something that was written with 
>>lazyPut.  lazyPut writes the offset of the end of the serialised data at
>>the beginning, so that lazyGet can skip over it, and subsequent gets 
>>start from the next item in the stream.
> the problem is what there is ONLY ONE read pointer, so it should be
> impossible to intersperse reading with `get` and consuming structure
> returned by `lazyGet`, either for BinMem or BinIO
> ... hmm, on the other side they don't interspersed because there is
> only one call to the unsafeInterleaveIO. closures returned by lazyGet
> just should be evaluated STRICTLY after all other `get` operation. and
> changing the `getAt` implementation to the following:
> getAt bh p = do p0 <- tellBin bh
>                 seekBin bh p
>                 a <- get bh
>                 seekBin bh p0
>                 return a
> should omit even this restriction

Ah yes, I forgot about this subtle restriction.  The underlying 
principle is that an individual 'get' or 'lazyGet' is atomic: it 
traverses the whole stream before returning a result.   There may be 
'lazyGet' components in the result, but each one of those is atomic in 
the same sense.  So the file pointer never needs to be set to two values 

It's a bit hacky, but it works nicely.

>>>can you  recommend me paper to read about using Haskell class system?
> well, how about this?

There are several papers at the level you're interested in, I think: 
Lennart's "Implementing Haskell Overloading" is a good one, and you 
might find "Type classes in Haskell" (Hall/Hammond/Peyton Jones/Wadler) 
useful, also "Implementing Type Classes" (Peterson/Jones).


More information about the Glasgow-haskell-users mailing list