====== Creating a Function Without Input Parameters (ST) ======

In Mervis IDE, it is fully supported to define a function in Structured Text (ST) that does not require any input parameters (i.e., it has no ''VAR_INPUT'' section).

This is useful for functions that return constant values, system states, or perform actions based on global variables/internal logic rather than arguments.

===== Syntax Example =====

If you attempt to skip the ''VAR_INPUT'' section, you must ensure your ''VAR_OUTPUT'' or local variables immediately follow the function declaration.

<code iec-st>
FUNCTION MyFunction : REAL
    VAR_OUTPUT
        outVal : REAL;
    END_VAR

    // Logic
    outVal := 5.0;

END_FUNCTION
</code>

===== Common Error =====
Users often encounter the error: ''In function declaration no viable alternative at input "VAR_OUTPUT"''.

This usually happens if the structure of the variable declaration block is malformed. Ensure that you declare the function return type (e.g., '': REAL'') correctly before starting the ''VAR_OUTPUT'' block.

===== Usage Example =====

**Declaration:**
<code iec-st>
FUNCTION GetPi : REAL
    VAR_OUTPUT
        val : REAL;
    END_VAR

    val := 3.14159;
END_FUNCTION
</code>

**Calling the function:**
Since there are no inputs, you can call the function with empty parentheses or simply by name, depending on the context:

<code iec-st>
PROGRAM Main
    VAR
        piValue : REAL;
    END_VAR

    piValue := GetPi(); 
END_PROGRAM
</code>