[project @ 2004-09-30 10:35:15 by simonpj]

------------------------------------
	Add Generalised Algebraic Data Types
	------------------------------------

This rather big commit adds support for GADTs.  For example,

    data Term a where
 	  Lit :: Int -> Term Int
	  App :: Term (a->b) -> Term a -> Term b
	  If  :: Term Bool -> Term a -> Term a
	  ..etc..

    eval :: Term a -> a
    eval (Lit i) = i
    eval (App a b) = eval a (eval b)
    eval (If p q r) | eval p    = eval q
    		    | otherwise = eval r


Lots and lots of of related changes throughout the compiler to make
this fit nicely.

One important change, only loosely related to GADTs, is that skolem
constants in the typechecker are genuinely immutable and constant, so
we often get better error messages from the type checker.  See
TcType.TcTyVarDetails.

There's a new module types/Unify.lhs, which has purely-functional
unification and matching for Type. This is used both in the typechecker
(for type refinement of GADTs) and in Core Lint (also for type refinement).

1 files changed, 9 insertions, 8 deletions

diff --git a/ghc/compiler/utils/Outputable.lhs b/ghc/compiler/utils/Outputable.lhs
index 22856f1a28..8b52867677 100644
--- a/ghc/compiler/utils/Outputable.lhs
+++ b/ghc/compiler/utils/Outputable.lhs
@@ -42,10 +42,10 @@ module Outputable (
 	showSDocUnqual, showsPrecSDoc,
 	pprHsChar, pprHsString,
 
-
 	-- error handling
-	pprPanic, pprPanic#, pprError, pprTrace, assertPprPanic, warnPprTrace,
-	trace, panic, panic#, assertPanic
+	pprPanic, assertPprPanic, pprPanic#, pprPgmError, 
+	pprTrace, warnPprTrace,
+	trace, pgmError, panic, panic#, assertPanic
     ) where
 
 #include "HsVersions.h"
@@ -470,12 +470,13 @@ speakNTimes t | t == 1 	   = ptext SLIT("once")
 %************************************************************************
 
 \begin{code}
-pprPanic :: String -> SDoc -> a
-pprError :: String -> SDoc -> a
+pprPanic, pprPgmError :: String -> SDoc -> a
 pprTrace :: String -> SDoc -> a -> a
-pprPanic  = pprAndThen panic
-pprError  = pprAndThen error
-pprTrace  = pprAndThen trace
+pprPanic    = pprAndThen panic		-- Throw an exn saying "bug in GHC"
+
+pprPgmError = pprAndThen pgmError	-- Throw an exn saying "bug in pgm being compiled"
+					--	(used for unusual pgm errors)
+pprTrace    = pprAndThen trace
 
 pprPanic# heading pretty_msg = panic# (show (doc PprDebug))
 			     where