Comparison functions

GT, GE, EQ, LE, LT, NE

The IEC standard provides function-form comparison operators in addition to the infix <, <=, =, >=, >, <>:

Function	Equivalent	Meaning
`GT(IN1, IN2): BOOL`	`IN1 > IN2`	Greater than
`GE(IN1, IN2): BOOL`	`IN1 >= IN2`	Greater than or equal
`EQ(IN1, IN2): BOOL`	`IN1 = IN2`	Equal
`LE(IN1, IN2): BOOL`	`IN1 <= IN2`	Less than or equal
`LT(IN1, IN2): BOOL`	`IN1 < IN2`	Less than
`NE(IN1, IN2): BOOL`	`IN1 <> IN2`	Not equal

In Structured Text these are equivalent to the infix operators and most projects use >, <, = directly. The function form has two genuine use cases:

In IL (Instruction List), where the accumulator-style syntax doesn’t have infix operators.
In variadic chained checks in ST — see below.

Variadic chained form

GT(IN1, IN2, IN3, ...) returns TRUE only when the values are strictly decreasing in order. Equivalent to (IN1 > IN2) AND (IN2 > IN3) AND ....

The same pattern applies to GE, LE, LT (chain in the matching direction). EQ, NE chain pairwise: EQ(IN1, IN2, IN3) := (IN1 = IN2) AND (IN2 = IN3).

(* "is x in (5, 10) exclusive?" — chained GT *)
xInRange := GT(10, iX, 5);

(* monotone-decreasing series check *)
xMonotonic := GT(iA, iB, iC, iD);

These chained forms read more cleanly than the equivalent infix-AND chain when the relation is the same throughout.

Type-matching rule

Same as the infix operators: all arguments must share a type. matiec is strict — see textual/structured-text/operators/comparison.

IEC reference

IEC 61131-3 third edition (2013), Annex F.2.4 — “Comparison functions” Table F.9.

matiec conformance

All six functions implemented per the standard, including the variadic chained form.