Built-in Natural literals in Core

Add support for built-in Natural literals in Core.

- Replace MachInt,MachWord, LitInteger, etc. with a single LitNumber
  constructor with a LitNumType field
- Support built-in Natural literals
- Add desugar warning for negative literals
- Move Maybe(..) from GHC.Base to GHC.Maybe for module dependency
  reasons

This patch introduces only a few rules for Natural literals (compared
to Integer's rules). Factorization of the built-in rules for numeric
literals will be done in another patch as this one is already big to
review.

Test Plan:
  validate
  test build with integer-simple

Reviewers: hvr, bgamari, goldfire, Bodigrim, simonmar

Reviewed By: bgamari

Subscribers: phadej, simonpj, RyanGlScott, carter, hsyl20, rwbarton,
thomie

GHC Trac Issues: #14170, #14465

Differential Revision: https://phabricator.haskell.org/D4212

1 files changed, 7 insertions, 1 deletions

diff --git a/compiler/iface/TcIface.hs b/compiler/iface/TcIface.hs
index 9d04bf2fb3..bffda71f0a 100644
--- a/compiler/iface/TcIface.hs
+++ b/compiler/iface/TcIface.hs
@@ -1367,9 +1367,15 @@ tcIfaceLit :: Literal -> IfL Literal
 -- Integer literals deserialise to (LitInteger i <error thunk>)
 -- so tcIfaceLit just fills in the type.
 -- See Note [Integer literals] in Literal
-tcIfaceLit (LitInteger i _)
+tcIfaceLit (LitNumber LitNumInteger i _)
   = do t <- tcIfaceTyConByName integerTyConName
        return (mkLitInteger i (mkTyConTy t))
+-- Natural literals deserialise to (LitNatural i <error thunk>)
+-- so tcIfaceLit just fills in the type.
+-- See Note [Natural literals] in Literal
+tcIfaceLit (LitNumber LitNumNatural i _)
+  = do t <- tcIfaceTyConByName naturalTyConName
+       return (mkLitNatural i (mkTyConTy t))
 tcIfaceLit lit = return lit
 
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