Add 'List.foldl1'

Author: ssoelvsten

lib/List.trp

@@ -83,6 +83,9 @@ let (* -- List Access -- *)
     fun foldl f y []    = y
       | foldl f y x::xs = foldl f (f (x,y)) xs
 
+    (** Left-fold of `f` on a non-empty list using the head as the initial value. *)
+    fun foldl1 f x::xs = foldl f x xs
+
     (* TODO: foldr *)
 
     (** Returns the sublist of elements that satisfy `f`. Not tail-recursive. *)
@@ -183,6 +186,7 @@ let (* -- List Access -- *)
         map,
         mapi,
         foldl,
+        foldl1,
         filter,
         filteri,
         partition,

tests/lib/List.golden

@@ -1,4 +1,4 @@
-2025-09-09T14:12:55.766Z [RTM] info: Skipping network creation. Observe that all external IO operations will yield a runtime error.
+2025-10-24T08:31:14.889Z [RTM] info: Skipping network creation. Observe that all external IO operations will yield a runtime error.
 begin List
   begin head
       [ TEST ] it returns 42 for [42]      [ PASS ] it returns 42 for [42]
@@ -91,6 +91,21 @@
       [ TEST ] it id [1,1]      [ PASS ] it id [1,1]
       [ TEST ] it id [1,3]      [ PASS ] it id [1,3]
   end 
+  begin foldl
+      [ TEST ] it sums 0 []      [ PASS ] it sums 0 []
+      [ TEST ] it sums 2 []      [ PASS ] it sums 2 []
+      [ TEST ] it sums 0 [1]      [ PASS ] it sums 0 [1]
+      [ TEST ] it sums 0 [1,1]      [ PASS ] it sums 0 [1,1]
+      [ TEST ] it sums 0 [1,3]      [ PASS ] it sums 0 [1,3]
+      [ TEST ] it sums 2 [1,3]      [ PASS ] it sums 2 [1,3]
+  end 
+  begin foldl1
+      [ TEST ] it sums [0]      [ PASS ] it sums [0]
+      [ TEST ] it sums [1]      [ PASS ] it sums [1]
+      [ TEST ] it sums [2]      [ PASS ] it sums [2]
+      [ TEST ] it sums [1,1]      [ PASS ] it sums [1,1]
+      [ TEST ] it sums [1,3]      [ PASS ] it sums [1,3]
+  end 
   begin filter
       [ TEST ] it isOdd  []      [ PASS ] it isOdd  []
       [ TEST ] it isEven []      [ PASS ] it isEven []
@@ -128,6 +143,6 @@
   end 
 end 
 
-Total:  90
-Passes: 90
+Total:  101
+Passes: 101
 >>> Main thread finished with value: true@{}%{}

tests/lib/List.trp

@@ -105,6 +105,25 @@ let val tests = Unit.group "List" [
                   , Unit.it "id [1,3]" (Unit.isEq [(0,1), (1,3)] (List.mapi id [1,3]))
                 ]
             end,
+            let fun sum (a,b) = a+b
+            in Unit.group "foldl" [
+                    Unit.it "sums 0 []"    (Unit.isEq 0 (List.foldl sum 0 []))
+                  , Unit.it "sums 2 []"    (Unit.isEq 2 (List.foldl sum 2 []))
+                  , Unit.it "sums 0 [1]"   (Unit.isEq 1 (List.foldl sum 0 [1]))
+                  , Unit.it "sums 0 [1,1]" (Unit.isEq 2 (List.foldl sum 0 [1,1]))
+                  , Unit.it "sums 0 [1,3]" (Unit.isEq 4 (List.foldl sum 0 [1,3]))
+                  , Unit.it "sums 2 [1,3]" (Unit.isEq 6 (List.foldl sum 2 [1,3]))
+                ]
+            end,
+            let fun sum (a,b) = a+b
+            in Unit.group "foldl1" [
+                    Unit.it "sums [0]"   (Unit.isEq 0 (List.foldl1 sum [0]))
+                  , Unit.it "sums [1]"   (Unit.isEq 1 (List.foldl1 sum [1]))
+                  , Unit.it "sums [2]"   (Unit.isEq 2 (List.foldl1 sum [2]))
+                  , Unit.it "sums [1,1]" (Unit.isEq 2 (List.foldl1 sum [1,1]))
+                  , Unit.it "sums [1,3]" (Unit.isEq 4 (List.foldl1 sum [1,3]))
+                ]
+            end,
             let val xs = [0,1,2,3,4,5,6,7,8,9]
                 fun isOdd  x = (x mod 2) = 1
                 fun isEven x = (x mod 2) = 0