About GHCi

I find that Haskell interpreter is rather difficult to use:
1."f=3" is a legal statement in Haskell, i.e. define "f" as 
a 
   constant function, but a parse error occurs.
  "let f=3" is illegal, "let" and "in" are used together, but
   it works in GHCi. 
2. if I happen to print out an infinite list, I don't know how 
   to interrupt it, when press Ctrl+C, GHCi just quit.
3. I can't use "import" to import modules. There are 
many sub 
   directories in the imports directory, but I don't know 
how to 
   import libraries in concurrent, win32, util, lang and 
objectio