Source code in the action! programming language

;;; returns TRUE(1) if p is prime by Wilson's theorem, FALSE(0) otherwise
;;;         computes the factorial mod p at each stage, so as to allow
;;;         for numbers whose factorial won't fit in 16 bits
BYTE FUNC isWilsonPrime( CARD p )
  CARD i, factorial_mod_p
  BYTE result

  factorial_mod_p = 1
  FOR i = 2 TO p - 1 DO
    factorial_mod_p = ( factorial_mod_p * i ) MOD p
  OD

  IF factorial_mod_p = p - 1 THEN result = 1 ELSE result = 0 FI

RETURN( result )

PROC Main()
  CARD i

  FOR i = 1 TO 100 DO
    IF isWilsonPrime( i ) THEN
       Put(' ) PrintC( i )
    FI
  OD
RETURN