[Haskell-cafe] Template Haskell -- when are things evaluated?

[Emil Axelsson]

Hello all!

Up until yesterday I thought I understood the basics of Template Haskell, but 
now I'm a little confused. Consider the following code

module A
   where
     a1 = [| (2::Int) + 2 |]

     a2 = let x = (2::Int) + 2 in [| x |]

     a3 = [| y |]
       where
         y = (2::Int) + 2

     z = (2::Int) + 2

     a4 = [| z |]

module B
   where
     import A

     a1S = $a1
     a2S = $a2
     a3S = $a3
     a4S = $a4

I'd have thought that in all four cases the addition was evaluated at 
compile-time, but compiling with -ddump-splices reveals that this is only the 
case for a2 and a3. Is there a general reliable rule for when things are evaluated?

Thanks,

/ Emil