Functions mapFst and mapSnd

[simantics/platform.git] / bundles / org.simantics.scl.runtime / scl / Prelude.scl

diff --git a/bundles/org.simantics.scl.runtime/scl/Prelude.scl b/bundles/org.simantics.scl.runtime/scl/Prelude.scl
index 5e5bd858b8b65e2a30210e388fd6de72ef1a747f..a926ae40ec3b0ca4ffb4c635132c3fa9eaa58f9e 100644 (file)
--- a/bundles/org.simantics.scl.runtime/scl/Prelude.scl
+++ b/bundles/org.simantics.scl.runtime/scl/Prelude.scl
@@ -1484,6 +1484,14 @@ fst (x,y) = x
 snd :: (a,b) -> b
 snd (x,y) = y
 
+@inline
+mapFst :: (a -> b) -> (a,c) -> (b,c)
+mapFst f (x,y) = (f x, y)
+
+@inline
+mapSnd :: (a -> b) -> (c,a) -> (c,b)
+mapSnd f (x,y) = (x, f y)
+
 instance (Ord a, Ord b) => Ord (a, b) where
     compare (a0, b0) (a1, b1) = compare a0 a1 &<& compare b0 b1
 
@@ -1949,7 +1957,7 @@ importJava "org.simantics.scl.runtime.Lists" where
     Given a list of values and a function computing a key for each value, the function produces a function that finds a value
     effeciently for the given key.
     """
-    indexBy ::  (a -> b) -> [a] -> b -> Maybe a
+    indexBy ::  (a -> <e> b) -> [a] -> <e> (b -> Maybe a)
     
     "Works like `index` but uses the given functions as hash codes and equality."
     indexWith :: (a -> Integer) -> (a -> a -> Boolean) -> [(a,b)] -> a -> Maybe b
@@ -2003,6 +2011,16 @@ 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.
 """