On 03 Dec 2007, at 13:25 , Tim Newsham wrote:
Probably one should understand how to use monads before worrying
about
the do-notation. Here are some references:
I don't totally agree. You can teach monads to beginners just fine
using the do-notation. Unsuprisingly its very much like teaching
monads using bind. You describe a two line do-block as the basic
building block for combining two actions into a single action:
do {
result1 <- act1
expr involving result1 building an act
}
By teaching >>= and return first in the context of monads, I think it
encourages seeing 'do' primarily as syntactic sugar, instead of some
mysterious construct in its own right. This lets you apply
everything you know about programming in pure, functional, typed
programming (e.g. Haskell, SML, etc.) to monads, by seeing the type
signature of >>= and return. This, in turn, lets you conclude that
monads are not mysterious at all, but simply a few operations whose
types work in concert. This doesn't mean you understand them, but it
removes certain potential confusions.
If you learn 'do' first, there is a tendency to think of "using
monads" and "using do" as synonymous, which they are not; and of
thinking that 'do' is performing some sort of magic on your types
(i.e. that you couldn't straightforwardly emulate 'do' with other
operations).
When you're first learning monads, you're constantly suspicious of
the mysterious, because of their name, their reputation, and their
putative generality and power. (I say 'putative' because when you're
learning you don't yet know that it's true. =])
I've had debates about what should be taught, and obviously not
everyone agrees, but at the least, its possible and reasonable
and understandable to teach do-notation first.
I don't think I can conclude that there are *no* reasons to teach the
do-notation first. I just think that it is more instructive to teach
it later.
Please understand I'm a relative newbie in Haskell, so I would
appreciate any comments on what I said above. I'm still trying to
learn. =]
-Denis
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