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)
FUNCTION_BLOCK STACK_INT
VAR_INPUT PUSH, POP: BOOL R_EDGE; (* Basic stack operations *)
R1 : BOOL ; (* Over-riding reset *)
IN : INT ; (* Input to be pushed *)
N : INT ; (* Maximum depth after reset *)
END_VAR
VAR_OUTPUT EMPTY : BOOL := 1 ; (* Stack empty *)
OFLO : BOOL := 0 ; (* Stack overflow *)
OUT : INT := 0 ; (* Top of stack data *)
END_VAR
VAR STK : ARRAY[0..127] OF INT; (* Internal stack *)
NI : INT :=128 ; (* Storage for N upon reset *)
PTR : INT := -1 ; (* Stack pointer *)
END_VAR
(* Function Block body *)
IF R1 THEN
OFLO := 0; EMPTY := 1; PTR := -1;
NI := LIMIT (MN:=1,IN:=N,MX:=128); OUT := 0;
ELSIF POP & NOT EMPTY THEN
OFLO := 0; PTR := PTR-1; EMPTY := PTR < 0;
IF EMPTY THEN OUT := 0;
ELSE OUT := STK[PTR];
END_IF ;
ELSIF PUSH & NOT OFLO THEN
EMPTY := 0; PTR := PTR+1; OFLO := (PTR = NI);
IF NOT OFLO THEN OUT := IN ; STK[PTR] := IN;
ELSE OUT := 0;
END_IF ;
END_IF ;
END_FUNCTION_BLOCK