[project @ 2000-07-11 15:58:26 by simonmar]

[ghc-hetmet.git] / ghc / compiler / utils / Maybes.lhs

diff --git a/ghc/compiler/utils/Maybes.lhs b/ghc/compiler/utils/Maybes.lhs
index ce92316..6dd9251 100644 (file)
--- a/ghc/compiler/utils/Maybes.lhs
+++ b/ghc/compiler/utils/Maybes.lhs
@@ -1,13 +1,14 @@
 %
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
 %
 \section[Maybes]{The `Maybe' types and associated utility functions}
 
 \begin{code}
 module Maybes (
---     Maybe(..), -- no, it's in 1.3
+       Maybe2(..), Maybe3(..),
        MaybeErr(..),
 
+       orElse, 
        mapMaybe,
        allMaybes,
        firstJust,
@@ -29,6 +30,21 @@ module Maybes (
 #include "HsVersions.h"
 
 import Maybe( catMaybes, mapMaybe )
+
+
+infixr 4 `orElse`
+\end{code}
+
+
+%************************************************************************
+%*                                                                     *
+\subsection[Maybe2,3 types]{The @Maybe2@ and @Maybe3@ types}
+%*                                                                     *
+%************************************************************************
+
+\begin{code}
+data Maybe2 a b   = Just2 a b   | Nothing2  deriving (Eq,Show)
+data Maybe3 a b c = Just3 a b c | Nothing3  deriving (Eq,Show)
 \end{code}
 
 
@@ -96,6 +112,10 @@ returnMaybe = Just
 
 failMaybe :: Maybe a
 failMaybe = Nothing
+
+orElse :: Maybe a -> a -> a
+(Just x) `orElse` y = x
+Nothing  `orElse` y = y
 \end{code}
 
 Lookup functions
@@ -165,3 +185,4 @@ returnMaB v = Succeeded v
 failMaB :: err -> MaybeErr val err
 failMaB e = Failed e
 \end{code}
+