PL/0: A minimalistic programming language
PL/0 is an educational language invented by Niklaus Wirth in his book "Compiler Construction". Therein PL/0 is presented as a subset of Pascal. There are some restrictions namely that procedures aren't parameterizable and the variable's and constant's type are implicitely and only int. The syntax used here has two small extensions to the original one presented in EBNF on Wikipedia.
Those extensions are:
program = "program" ident block "." .
ifStatement = "if" condition "then" statement "else" statement
Besides those structural additions, every keyword here can be typed in both all uppercase or all lowercase letters.
This language was contributed by Jan Reimann.