While Language Specification

Syntactic Categories

P	Programs
V	Variable declarations
S	Statements
x, y	Variables
n	Numerals
a	Arithmetic expressions
b	Boolean expressions
opa	Arithmetic operators: +, -, /, *, %
opb	Boolean operators: and, or, xor
opr	Relational operators: ==, !=, <, >, <=, >=
opbt	Bitwise operators: <<, >>, &, |, ^

Abstract Syntax

Programs P:

• S

Variable declarations V:

• V1 ; V2
• var x

Statements S:

• begin V ; S end
• S1 ; S2
• skip
• if b then S1 else S2
• while b do S
• write a
• write b
• read x

Boolean expressions b:

• true
• false
• ( b )
• not b
• b1 opb b2
• a1 opr a2

Arithmetic expressions a:

• ( a )
• - a
• x
• n
• a1 opa a2
• a1 opbt a2

Example

While program calculating factorial is here:

begin
  var x;
  var y;
  var z;
  read x;
  y := x;
  z := 1;
  while y > 1 do
    z = z * y;
    y = y - 1
  write y
end