[Haskell-cafe] Trapped by the Monads

Lennart Augustsson lennart at augustsson.net
Tue Sep 20 16:11:40 EDT 2005

Mark Carter wrote:
> The typical example in C is:
> mem = malloc(1024)
> Malloc returns 0 to indicate that memory cannot be allocated, or a 
> memory address if it can. The variable mem is a so-called hybrid 
> variable; it crunches together 2 different concepts: a boolean value 
> (could I allocate memory?) and an address value (what is the address 
> where I can find my allocated memory).
> It's considered a bad idea because it makes it easy for programmers to 
> use the value inappropriately - witness the number of programmers who 
> pass in 0 as a memory location. 

This is a bad idea in C, because you cannot force programmers to test
the return value properly.

The Maybe type in Haskell is a good idea, because you must test the
a Maybe value to extract the real value.  (Using the Maybe monad this
can be hidden.)

	-- Lennart

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