[Haskell-cafe] Haskell Propeganda

Don Stewart dons at galois.com
Thu Aug 28 02:41:50 EDT 2008

> Aaron Tomb <atomb at galois.com> writes:
> >> Huh? Type safety buys [...] nothing about dereferencing null
> >> pointers, which are the moral equivalent of Nothing.
> > What type safety buys you, in my mind, is that Nothing is only a valid
> > value for explicit Maybe types. In cases where you don't use Maybe,
> > the "null" situation just can't occur. In languages with null
> > pointers, any pointer could possibly be null.
> To write Haskell that is obviously safe, you need to check all cases
> of algebraic data types - both Just and Nothing.
> To do something similar in C, you need to check every pointer for NULL.  
> The great thing about Maybe is that once I've checked it isn't
> Nothing, I can extract the value and dispense with further checks.
>   foo mbx = maybe default (bar x) mbx

And GHC will warn me when I forget to check all cases, and prevent me
from compiling at all, if I don't do any check.

-- Don

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