Editing Conditional (computer programming) (section)

===Guarded conditionals===

The [[Guarded Command Language]] (GCL) of [[Edsger W. Dijkstra|Edsger Dijkstra]] supports conditional execution as a list of commands consisting of a Boolean-valued [[Guard (computer science)|guard]] (corresponding to a ''condition'') and its corresponding statement. In GCL, exactly one of the statements whose guards is true is evaluated, but which one is arbitrary. In this code
 '''if''' G0 → S0
  □ G1 → S1
 ...
  □ Gn → Sn
 '''fi'''
the G<sub>''i''</sub>'s are the guards and the S<sub>''i''</sub>'s are the statements. If none of the guards is true, the program's behavior is undefined.

GCL is intended primarily for reasoning about programs, but similar notations have been implemented in [[Concurrent Pascal]] and [[Occam (programming language)|occam]].