Functor

• Functional XSLT/XPath/XQuery - #2 Functor pattern 3 June 2024

  Functional XSLT/XPath/XQuery - #2 Functor pattern

  In the previous blog we introduced some machinery, the id function, and function composition, we talked about function types, and invented an informal notion of parametric types in order to aid our thinking.

  We now move onto the functional patterns. These are a bit like OO patterns but have more formal mathematical underpinnings. Knowing what to call the things is problematic in itself, in mathematics these underpinnings are called a category, in functional circles they are often called a typeclass , this is a borrowed term from Haskell that has a particular mechanism for implementing them which may be misleading, other languages have different mechanisms, some languages have no formal mechanism, but have informal mechanisms, or no mechanism at all apart from idiomatic usage, like an OO pattern.