Correctly identify errors when parsing erroneous code (make sure flex goes back to INITIAL state when code contains errors that do not allow determining whether ST or IL is being parsed)
(* Following taken directly from the IEC 61131.3 draft standard *)
(*
* An IEC 61131-3 IL and ST compiler.
*
* Based on the
* FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)
*
*)
FUNCTION_BLOCK DERIVATIVE
VAR_INPUT
RUN : BOOL ; (* 0 = reset *)
XIN : REAL ; (* Input to be differentiated *)
CYCLE : TIME ; (* Sampling period *)
END_VAR
VAR_OUTPUT
XOUT : REAL ; (* Differentiated output *)
END_VAR
VAR X1, X2, X3 : REAL ; END_VAR
IF RUN THEN
XOUT := (3.0 * (XIN - X3) + X1 - X2)
/ (10.0 * TIME_TO_REAL(CYCLE)) ;
X3 := X2 ; X2 := X1 ; X1 := XIN ;
ELSE XOUT := 0.0; X1 := XIN ; X2 := XIN ; X3 := XIN ;
END_IF ;
END_FUNCTION_BLOCK