:p in GHCi debugger is broken for Integer

[igloo]

:p used to do this for Integers:

Prelude> let i = Just (10::Integer)
Prelude> :p i
i = Just 10

but it now does this:

Prelude> let i = Just (10::Integer)
Prelude> :p i
i = Just (_t1::Integer)

but I can't see an obvious reason why.

[mnislaih]

Imho there is nothing fundamentally broken with :p in this example. It just shows that GHC has become a little lazier w.r.t. Integers. I have tried but can't find the exact patch producing this change, but it seems to be due to the move of Integer into its own package.

By its nature, imho it is not reasonable to expect that the output of :print will remain the same across GHC versions, as the evaluation strategy in Haskell is not defined and GHC may change it over different versions.

[igloo]

OK, I now understand what's going on. We used to make S# 10#, which is fully evaluated so got printed. We now make smallInteger 10# which is not fully evaluated. So the new behaviour seems fine to me. I've updated the test accordingly.

[simonmar]

Are we sure that nothing has regressed w.r.t. efficiency here?

[igloo]

The definition is just

{-# INLINE smallInteger #-}
smallInteger :: Int# -> Integer
smallInteger i = S# i

so there should be no difference when compiling.