Basic functions

Question 1

Explain:

fold functions (reduce)

Answer 1

This is family of higher-order functions which are used to transform/fold/reduce a data structure to a value by application of a provided function to the elements of the structure.

There are various approaches to folding but the most interesting are

• foldl - left fold ((((0 + 1) + 2) + 3) + 4)
  
  • fails for infinite lists, builds up memory leaks
• foldr - right fold (0+ (1 + (2 + (3 +4))))
  
  • can work with infinite lists with special care.

Intuition with folds is that they are replacing the constructor in a data structure to produce the effect of reduction of the structure.

Lot of other function can be implemented as folds: inverse, map…