An anonymous language devised by
EwDijkstra for the examples in his book
A Discipline of Computer Programming. Dijkstra did not implement its language. The term
egg refers to a recent Java implementation which is available at
http://www.andrewcooke.free-online.co.uk/jara/egg/ .
- It is a block-structured imperative language in the Algol tradition.
- It has GuardClauses and guarded command sets. A guarded statement only executes if its accompanying condition (guard) is true. A set of GuardClauses can be written as part of an if or do statement, with the semantics described in GuardClause. These constructs replace all flow-of-control constructs in procedural languages, but are easier to prove correct.
- Variables are local or global, with special consideration given to uninitialized globals.
- The only aggregate structure is one-dimensional arrays whose bounds can be adjusted at run time. (Essentially indexible dequeues.)
Here is
EuclidOfAlexandria's GCD algorithm, taken from the distribution:
begin privar X, Y, x, y ;
X vir int, Y vir int := 12345 * 9876, 12345 * 6789 ;
if X > 0 and Y > 0 ->
x vir int, y vir int := X, Y ;
do x > y -> x := x - y | y > x -> y := y - x od ;
print( x ) { for 12345 * 9876, 12345 * 6789 answer is 37035 }
fi
end
According to the
LanguageList Dijkstra "later (1972) referred to this language as DOVPA (Dijkstra's Own Version of Pidgin Algol)".