%%file: proglang.pro
%%  line: some knowledge about programming languages

%language(L) means L is a programming language

language(smalltalk).
language(lisp).
language(prolog).


% essence (L, DT, CF) means language L features datatype DT and
% computational formalism CF

essence(smalltalk, objects,'message passing').
essence(lisp, lists,'recursive functions').
essence(prolog, relations,'logical inferencing').


% history(L, I, D) means language L was invented by I in year D

history(smalltalk, inventor('Alan Kay'), date(1980)).
history(lisp, inventor('John McCarth'), date(1959)).
history(prolog, inventor('Alan Colmeraur'), date(1971)).