An Intuition for List Folds
summary
Defines a cons list as nil or cons and gives precise rules: left fold is a loop used for sum, product, length, reverse (linear time by flipping cons), and fails on infinite lists; right fold replaces constructors so it implements map, append, flatten, filter, headOr and can work on infinite lists when the replacing function is lazy. Shows Haskell code, warns JVM foldr causes StackOverflow for large lists, and demonstrates sequence via foldr with lift-to-cons and return.
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chapters (8)
- 0:00Start
- 12:03How Do You Reverse a List
- 21:01Appending to Lists
- 23:17Mapping a Function on a List
- 26:33Function Composition
- 27:22Flattening a List of Lists
- 29:50Favorite Functions
- 45:31Length Function
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