Parametric Programming – an equational approach to OO and beyond | Bill Wadge's Blog
A very long time ago I had an interesting if flawed idea. The idea was to (optionally) replace instances of expression constructs with equations defining or referring to components of conventional compound structures. The special variables defined or used I called “pronouns” but now I prefer “parameters”.
The new paradigm allows a purely equational approach to something like OO and in particular allows an OO extension of Lucid that is simple and natural. But parametric programming (PP) seems to go beyond OO. It can be used in conjunction with other declarative languages like Haskell.
First we need to avoid where clauses, which complicate the issues. When I was at Warwick in the old days there was a band of enthusiastic devotees of the pioneering system language BCPL. BCPL was a descendant of the monster (and unimplemented) language CPL, and an ancestor (via B) of C itself.
Anyway BCPL had many nice features including the VALOF construct. A VALOF was like a begin-end block except that you use a command RESULTIS to return a value. For example
