Dijkstra's guarded command language

Edsger W. Dijkstra, about 1974

This language introduced the concept of guards and committed choice [=don't care] nondeterminism. It was described and used (but not named) in A Discipline of Programming, Edsger W. Dijkstra, Prentice-Hall 1976. Dijkstra later (1972) referred to this language as DOVPA.