From: Tuukka Lehtonen <tuukka.lehtonen@semantum.fi>
Date: Thu, 21 Jun 2018 15:01:28 +0000 (+0300)
Subject: Added Prelude/maybe
X-Git-Tag: v1.43.0~136^2~453
X-Git-Url: https://gerrit.simantics.org/r/gitweb?a=commitdiff_plain;h=refs%2Fchanges%2F75%2F1875%2F1;p=simantics%2Fplatform.git

Added Prelude/maybe

`maybe def f v` returns `def` if `v=Nothing` and `f x` if `v=Just x`.

gitlab #31

Change-Id: I3319ee8e9e4cf678aece4878c1fb2ddf33395bc4
---

diff --git a/bundles/org.simantics.scl.runtime/scl/Prelude.scl b/bundles/org.simantics.scl.runtime/scl/Prelude.scl
index 751294a11..03eabb66f 100644
--- a/bundles/org.simantics.scl.runtime/scl/Prelude.scl
+++ b/bundles/org.simantics.scl.runtime/scl/Prelude.scl
@@ -1290,8 +1290,12 @@ fromMaybe :: a -> Maybe a -> a
 fromMaybe default maybeValue = match maybeValue with
     Just v -> v
     _ -> default
-    
-    
+
+"`maybe def f v` returns `def` if `v=Nothing` and `f x` if `v=Just x`."
+maybe :: b -> (a -> <e> b) -> Maybe a -> <e> b
+maybe n _ Nothing  = n
+maybe _ f (Just x) = f x
+
 """
 Provides a default value if the first parameter is Nothing.
 The default value is evaluated only if needed. The function