Pretty-printing of the * kind

Before this patch, GHC always printed the * kind unparenthesized.

This led to two issues:

1. Sometimes GHC printed invalid or incorrect code.
   For example, GHC would print:  type F @*   x = x
         when it meant to print:  type F @(*) x = x
   In the former case, instead of a kind application we were getting a
   type operator (@*).

2. Sometimes GHC printed kinds that were correct but hard to read.
   Should  Either * Int  be read as  Either (*) Int
                              or as  (*) Either Int  ?
   This depends on whether -XStarIsType is enabled, but it would be
   easier if we didn't have to check for the flag when reading the code.

We can solve both problems by assigning (*) a different precedence. Note
that Haskell98 kinds are not affected:

  ((* -> *) -> *) -> *  does NOT become  (((*) -> (*)) -> (*)) -> (*)

The parentheses are added when (*) is used in a function argument
position:

   F * * *   becomes  F (*) (*) (*)
   F A * B   becomes  F A (*) B
   Proxy *   becomes  Proxy (*)
   a * -> *  becomes  a (*) -> *

0 files changed, 0 insertions, 0 deletions