> What I should have been told about upfront: > - the syntax for an expression > - the syntax for a block
Don't see your point. > - the adhoc syntax rules (how to distinguish among a tuple and a > pharanthesized expression and how to find the start and end of a block for > example ) Oh, that's pretty easy, parenthesized expression is not divided by a comma. > - what guarantees are made by the LANGUAGE that an IO action (such as do > putStrLn "Hello world" ) is not performed twice There are no such guarantees. If you write a = putStrLn "Hello world" main = do {a; a;} then your putStrLn would be performed twice. IO actions are first-class values, that's a feature, not a bug. > - the lambda expressions can be written (input) but cannot be printed > (output) Yes, since two different lambda expressions can denote the same function. > Here is some strange example: > module Hugs where > aa::Int > aa=7 > cc:: (Int->Int)->(Int->Int->Int)->Int->(Int->Int) > cc a op b = \x-> case x of { _ | x==aa -> x+1 ; _-> a x `op` b } > f::Int->Int > f(1)=1 > f(2)=2 > f(_)=3 > g::Int->Int > g(1)=13 > g(2)=23 > g(_)=33 > h::[Int->Int] -> Int ->Int > h [] x = x > h [rr] x = let { u=Hugs.f ; v=Hugs.g } in case rr of { u -> > Hugs.g(x)+aa ; v -> Hugs.f(x)+aa ; _ ->rr (x) + aa } > h (rr:ll) x = h [rr] x + h (ll) x > What I don't understand is why I'm forced to use guards like x==aa in cc, > when aa is clearly bounded (is 7) and why in function h, the bounded u and > v become free variables in the case expression. No, pattern matching bounds variables; if you write "case x of {aa -> ...} then aa becomes a LOCAL variable for the case statement, and shadows the global definition. The same applies to u and v in h, except that in this case local variables shadow upper-level local variables. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe