Motivation

``infrastructure'' functions are (mostly) obvious and tedious to write;

pretty printers, parsers, equality and comparisions, maps and folds

polytypic programming relieve this tedium by allowing a programmer to write a function once and apply it at many datatypes

Common functions:

• eq
• size
• show / read
• encode / decode
• forall, exists
• map, fold

Larger applications:

• pattern matching
• unification
• term rewriting
• generalized data-structures (generalized tries, zipper/navigator)