G'day.
Quoting Casey Rodarmor
Haskell is great!
Glad you think so. It proves you have good taste. :-)
Why is this:
(+ 1)
a curried invocation of the the plus operator, but this:
(+ 1 2)
is an error?
The plus sign is an infix operator. Putting it in parentheses is how you express it as a function, so if you want to apply the "plus" function to two arguments, this is how you'd express it: (+) 1 2 The syntax (+ 1), on the other hand, is slightly different. Even though it looks like a curried function, it's actually not. It's a special piece of syntax called an "operator section". If it helps, the arguments are actually the wrong way around for it to be a curried function. For a commutative operator like (+) this may not make a difference, but for other operators, it does. (>>= k), for example is not the same as ((>>=) k). Actually, it's a shorthand for (\m -> m >>= k). If you wanted ((>>=) k), you'd use (k >>=) instead.
And in the same vein, why is this a negative number:
(- 1)
instead of a curried invocation of the subtraction operator?
This was a hard design decision to make. People want to express negation with the minus sign, but it interferes with the operator section syntax. The rule can be thought of as: If it looks like a negation, then it is, otherwise it's an operator section.
Why can't I do this:
1 `(+)` 2
even if it is a little pathological?
The backquote notation is for turning _identifiers_ into operators, not general expressions. It would be nice to have a syntax for turning general expressions into operators, but Haskell doesn't have one.
And this might be a little implementation dependent, although I'll hazard it anyways: Why can't I assign to things when running GHCi?
You can do this with let syntax: Prelude> let x = product [1..10] Prelude> x+2 3628802 Cheers, Andrew Bromage