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Task/Catamorphism/EchoLisp/catamorphism.echolisp

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+;; rem : the foldX family always need an initial value
+;; fold left a list
+(foldl + 0 (iota 10)) ;; 0 + 1 + .. + 9
+  → 45
+
+;; fold left a sequence
+(lib 'sequences)
+(foldl * 1 [ 1 .. 10])
+    → 362880 ;; 10!
+
+;; folding left and right
+(foldl / 1 ' ( 1 2 3 4))
+    → 8/3
+(foldr / 1 '(1 2 3 4))
+    → 3/8
+
+;;scanl gives the list (or sequence) of intermediate values :
+(scanl * 1 '( 1 2 3 4 5))
+   → (1 1 2 6 24 120)