Understanding pattern matching with cons operator
- by Mathias
In "Programming F#" I came across a pattern-matching like this one (I simplified a bit):
let rec len list =
match list with
| [] -> 0
| [_] -> 1
| head :: tail -> 1 + len tail;;
Practically, I understand that the last match recognizes the head and tail of the list. Conceptually, I don't get why it works. As far as I understand, :: is the cons operator, which appends a value in head position of a list, but it doesn't look to me like it is being used as an operator here. Should I understand this as a "special syntax" for lists, where :: is interpreted as an operator or a "match pattern" depending on context? Or can the same idea be extended for types other than lists, with other operators?
