From: Tuukka Lehtonen <tuukka.lehtonen@semantum.fi>
Date: Thu, 23 Nov 2017 22:00:21 +0000 (+0200)
Subject: Added function elemIndex to SCL Prelude
X-Git-Tag: v1.31.0~21
X-Git-Url: https://gerrit.simantics.org/r/gitweb?a=commitdiff_plain;h=46ea0d713406fbd0a0d8a8e5f41b7fb8ea7001c3;p=simantics%2Fplatform.git

Added function elemIndex to SCL Prelude

refs #7639

Change-Id: I927c447e0e5a1d6102172c8d99f36c4a79e9138a
---

diff --git a/bundles/org.simantics.scl.runtime/scl/Prelude.md b/bundles/org.simantics.scl.runtime/scl/Prelude.md
index 36b6023c9..df91f29d1 100644
--- a/bundles/org.simantics.scl.runtime/scl/Prelude.md
+++ b/bundles/org.simantics.scl.runtime/scl/Prelude.md
@@ -37,7 +37,7 @@
 
 ::class[Sequence]
 ::value[!, getList]
-::value[elem]
+::value[elem, elemIndex]
 ::value[filter, concatMap]
 ::value[foldl, foldl1, foldr]
 ::value[unfoldl, unfoldr]
diff --git a/bundles/org.simantics.scl.runtime/scl/Prelude.scl b/bundles/org.simantics.scl.runtime/scl/Prelude.scl
index 6acbf924b..c04cc8625 100644
--- a/bundles/org.simantics.scl.runtime/scl/Prelude.scl
+++ b/bundles/org.simantics.scl.runtime/scl/Prelude.scl
@@ -2003,6 +2003,16 @@ elemMaybe el m = match m with
     Just el2 -> el == el2
     Nothing -> False
 
+"`elemIndex el lst` returns the index of the first element in the given list `lst` which is equal (by ==) to the query element, or Nothing if there is no such element."
+elemIndex :: a -> [a] -> Maybe Integer
+elemIndex el l = loop 0
+  where
+    len = length l
+    loop i | i < len = if el == l!i
+                       then Just i
+                       else loop (i+1)
+           | otherwise = Nothing
+
 """
 Computes a list that contains only elements that belongs to both input lists.
 """