Linear types (#15981)

This is the first step towards implementation of the linear types proposal
(https://github.com/ghc-proposals/ghc-proposals/pull/111).

It features

* A language extension -XLinearTypes
* Syntax for linear functions in the surface language
* Linearity checking in Core Lint, enabled with -dlinear-core-lint
* Core-to-core passes are mostly compatible with linearity
* Fields in a data type can be linear or unrestricted; linear fields
  have multiplicity-polymorphic constructors.
  If -XLinearTypes is disabled, the GADT syntax defaults to linear fields

The following items are not yet supported:

* a # m -> b syntax (only prefix FUN is supported for now)
* Full multiplicity inference (multiplicities are really only checked)
* Decent linearity error messages
* Linear let, where, and case expressions in the surface language
  (each of these currently introduce the unrestricted variant)
* Multiplicity-parametric fields
* Syntax for annotating lambda-bound or let-bound with a multiplicity
* Syntax for non-linear/multiple-field-multiplicity records
* Linear projections for records with a single linear field
* Linear pattern synonyms
* Multiplicity coercions (test LinearPolyType)

A high-level description can be found at
https://ghc.haskell.org/trac/ghc/wiki/LinearTypes/Implementation
Following the link above you will find a description of the changes made to Core.
This commit has been authored by

* Richard Eisenberg
* Krzysztof Gogolewski
* Matthew Pickering
* Arnaud Spiwack

With contributions from:

* Mark Barbone
* Alexander Vershilov

Updates haddock submodule.

1 files changed, 4 insertions, 3 deletions

diff --git a/compiler/GHC/Tc/Module.hs b/compiler/GHC/Tc/Module.hs
index f6e5b87f53..5ef192befe 100644
--- a/compiler/GHC/Tc/Module.hs
+++ b/compiler/GHC/Tc/Module.hs
@@ -1274,7 +1274,7 @@ checkBootTyCon is_boot tc1 tc2
          check (map flSelector (dataConFieldLabels c1) == map flSelector (dataConFieldLabels c2))
                (text "The record label lists for" <+> pname1 <+>
                 text "differ") `andThenCheck`
-         check (eqType (dataConUserType c1) (dataConUserType c2))
+         check (eqType (dataConWrapperType c1) (dataConWrapperType c2))
                (text "The types for" <+> pname1 <+> text "differ")
       where
         name1 = dataConName c1
@@ -2446,7 +2446,7 @@ getGhciStepIO = do
                      { hst_tele = mkHsForAllInvisTele
                                   [noLoc $ UserTyVar noExtField SpecifiedSpec (noLoc a_tv)]
                      , hst_xforall = noExtField
-                     , hst_body  = nlHsFunTy ghciM ioM }
+                     , hst_body  = nlHsFunTy HsUnrestrictedArrow ghciM ioM }
 
         stepTy :: LHsSigWcType GhcRn
         stepTy = mkEmptyWildCardBndrs (mkEmptyImplicitBndrs step_ty)
@@ -2965,7 +2965,8 @@ ppr_datacons debug type_env
   = ppr_things "DATA CONSTRUCTORS" ppr_dc wanted_dcs
       -- The filter gets rid of class data constructors
   where
-    ppr_dc dc = ppr dc <+> dcolon <+> ppr (dataConUserType dc)
+    ppr_dc dc = sdocWithDynFlags (\dflags ->
+                ppr dc <+> dcolon <+> ppr (dataConDisplayType dflags dc))
     all_dcs    = typeEnvDataCons type_env
     wanted_dcs | debug     = all_dcs
                | otherwise = filterOut is_cls_dc all_dcs