Monoids

• Functional XSLT/XPath/XQuery - #4 Monoid 9 June 2024

  Functional XSLT/XPath/XQuery - #4 Monoid

  Usually in these sorts of tutorials Monoid comes first, its the simplest, easiest most familiar sort of thing, we don’t really even need code to describe it, its loosely the theory of having something you can composing two things together and getting another thing of the same type, together with an identity element, so in mathematics the integers form a monoid with + and the identity element is 0 or we can use multiplication * and 1, the set of booleans, i.e. { True , False } together with the operator AND form a monoid, where the identity element is True, to be honest, these things are rarely used as monoids in functional code, they could be, there just isn’t much use, the things that are usually used as monoids are collections, so in the XPath world this is sequence, array, map (and the recently added maybe).