Yikes. I have been doing a fair bit of productive programming in Haskell, thinking that I am making a bit of progress. Then I hit something that is apparently *really simple* that I do not understand at all. How discouraging. Here is the code that makes me realize I don't understand types or type inference very well at all yet: f :: a f = 1 When I try to load the above, ghci gives me: No instance for (Num a) arising from the literal `2' In the expression: 2 In an equation for `f': f = 2 Failed, modules loaded: none. Ok, so then I try: g:: (Num a) => a g = 2 This compiles. Why? I mean, why is the first example (defining f) wrong, but the second example (defining g) ok? A slight variation on this is: h:: a h = 'a' to which ghci replies: Couldn't match type `a' with `Char' `a' is a rigid type variable bound by the type signature for c :: a at /Users/David/Project/EoP/ch04/weak.hs:114:1 In the expression: 'a' In an equation for `c': c = 'a' This last example is probably the most basic one which I need to understand. But, why is the problem apparently a different one than in the definition of "f" above? Of course, I cannot think of a reason to actually define things as shown above under ordinary circumstances. The code above is just boiled down to the simplest case I could find to illustrate my confusion. I guess I interpret "f::a" to mean "f is some (any) type a". So why can't it be whatever "1" is, which I suppose is Integer. What is the type system looking for? And why does the constraint (Num a) make things ok? Please point me in the direction of any reading I should do to clear up my confusion. TIA. - Jake -