Andy,

Template Haskell appears to be doing renaming during pretty printing. Take this example, that both prints the AST directly, as well as pretty printing.

*Main> runQ ([| let x = 1 in x |]) >>= \x -> print (pprint x,x) ("let x_0 = 1\n in x_0",LetE [ValD (VarP x_7) (NormalB (LitE (IntegerL 1))) []] (VarE x_7))

The var x has name x_7 in the AST, but x_0 in the pretty printed version.

Can someone comment on why this is done?

From my knowledge its the way GHC handles identifiers. GHC's AST does not contain source location information, so there is no way to distinguish between different identifiers in an AST. GHC renames them so they are unique to avoid this ambiguity. If you take another Haskell compiler such as Programatica - Programatica gets around using unique names for identifiers by adding location information as well, so you can can refer to a particular identifier by its source location. Chris.