From 0659f8eab66e6d6145f848e88742f9ecc385ea0f Mon Sep 17 00:00:00 2001
From: Camil Staps
Date: Mon, 20 Apr 2015 22:17:14 +0200
Subject: Added semistandard libs

---
 fp2/week1/camil/StdMaybe.dcl | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 fp2/week1/camil/StdMaybe.dcl

(limited to 'fp2/week1/camil/StdMaybe.dcl')

diff --git a/fp2/week1/camil/StdMaybe.dcl b/fp2/week1/camil/StdMaybe.dcl
new file mode 100644
index 0000000..2403683
--- /dev/null
+++ b/fp2/week1/camil/StdMaybe.dcl
@@ -0,0 +1,41 @@
+definition module StdMaybe
+
+//	********************************************************************************
+//	Clean StdLib library module, version 1.0
+//	********************************************************************************
+
+from StdFunc import :: St;
+from StdOverloaded import class ==(..);
+
+::	Maybe x
+	=	Just x
+	|	Nothing
+
+isJust		:: !(Maybe .x) -> Bool		// case @1 of (Just _) -> True; _ -> False
+isNothing	:: !(Maybe .x) -> Bool		// not o isJust
+fromJust	:: !(Maybe .x) -> .x		// \(Just x) -> x
+
+// for possibly unique elements:
+u_isJust :: !u:(Maybe .x) -> (!Bool, !u:Maybe .x)
+u_isNothing :: !u:(Maybe .x) -> (!Bool, !u:Maybe .x)
+
+accMaybe :: .(St .x .a) !u:(Maybe .x) -> (!Maybe .a,!u:Maybe .x)
+// accMaybe f (Just x) = (Just (fst (f x)),Just (snd (f x)))
+// accMaybe f Nothing  = (Nothing,Nothing)
+
+mapMaybe	:: .(.x -> .y) !(Maybe .x) -> Maybe .y
+// mapMaybe f (Just x) = Just (f x)
+// mapMaybe f Nothing  = Nothing
+
+instance ==       (Maybe x) | == x
+//	Nothing==Nothing
+//	Just a ==Just b <= a==b
+
+maybeToList :: !(Maybe .a) -> [.a];
+//	returns list with no or one element
+
+listToMaybe :: ![.a] -> .Maybe .a;
+//	returns Just head of list if possible
+
+catMaybes :: ![Maybe .a] -> .[.a];
+//	catMaybes ms =  [ m \\ Just m <- ms ]
-- 
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