Also, these laws are immensely valuable to compilers. The Haskell foldr/build rewrite rule allows for intermediate lists to be eliminated altogether[0], so you

Also, these laws are immensely valuable to compilers. The Haskell foldr/build rewrite rule allows for intermediate lists to be eliminated altogether[0], so you can write sum (map square [1..n]) and the compiler will remove the intermediate list altogether, putting a tail-recursive loop in the expression's place. [0] Paper on deforestation https://link.springer.com/content/pdf/10.1007%2F3-540-19027-9_23.pdf https://link.springer.com/content/pdf/10.1007%2F3-540-19027-...