[Haskell-beginners] IO ( stuff )

[Brent Yorgey]

> Does "impurity" from something
> like a random number generator or file I/O have to move it's way all
> the way through my code?

No, only through the parts that actually have to do file I/O or
generate random numbers or whatever.  However, cleanly separating the
IO code from the non-IO/"pure" code takes some experience.  It does
seem to be a common experience of people learning Haskell that IO ends
up "infecting" everything, even stuff that shouldn't have to do any
IO, but with good design this is not necessary.

In your particular case, your matrix generation function does depend
on random number generation so it makes sense that its type must
involve IO. However, if you go on to write other functions which do
deterministic operations on matrices, their types should *not* involve
IO, even if you pass randomly generated matrices to them as
arguments.

-Brent