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Expression Language Syntax

As its name suggests, everything in the expression language is an "expression". This means that everything returns a value. 5 is an expression. So is 5+1. So are {MyTags/TankLevel} and {MyTags/TankLevel}+1. Expressions can be combined in many powerful ways. Lets take a look at how expressions are written.

 

More formally, an expression is:

A Number
A Boolean
A String
A bound SQLTag
A bound property
A function call
A Dataset access
An equation involving any of these

Literal Values

Literal values are things like numbers, booleans, and strings that are represented directly in the language. In the expression language, numbers can by typed in directly as integers, floating point values, or using hexadecimal notation with a 0x prefix. Examples:

42

8.927

0xFFC2

 

Strings are represented by surrounding them with double or single quotes. You can use the backslash character to escape quotes that you want to be included in the string. Examples:

"This is a regular string"

'This one uses single quotes'

"This string uses \"escaping\" to include quotes inside the string"

 

Operators

You can use these arithmetic, logical, and bit-shifting operators to combine expressions.

-

Unary Minus

Negates a number.

!

Not

Logical opposite of a boolean

^

Power

Raises a number to the power of another number. a^b is ab

%

Modulus

Modulus or remainder of two numbers. a%b is the remainder of a÷b

*

Multiply


/

Divide


+

Add / Concatenate

If both operands are numbers, this will add them together. Otherwise treats arguments as strings and performs concatenation.

-

Subtraction


&

Bitwise AND


|

Bitwise OR


xor

Bitwise XOR


<<

Left Shift

A signed bitwise left shift

>>

Right Shift

A signed bitwise right shift

>

Greater Than

Logical greater-than test between two numbers. Returns a boolean.

<

Less Than


>=

Greater or Equal


<=

Less or Equal


=

Equal

Tests for equality between two operands.

!=

Not Equal

Tests for equality, returning true when not equal

&&

Logical AND

Returns true when both operands are true. Anything non-zero is considered true.

||

Logical OR

Returns true when either operand is true. Anything non-zero is considered true.

like

Fuzzy string matching

Compares the left-hand value with the pattern on the right side. The pattern may consist of %,*, and ? wildcards.

 

Bound Values

Bound values are paths to other values enclosed in braces. These will appear red in the expression editor. When you are writing an expression for a Expression Binding, you can reference tag values and property values using the brace notation. When you are writing an expression for an Expression Tag, you can only reference other tag values. You can use the Insert Property ( link ) and Insert Tag Value ( tag_blue_16 ) buttons to build these references for you.

Dataset Access

If you have an expression that returns a Dataset, you can pull a value out of the datatset using the dataset access notation, which takes one of these forms:

Dataset_Expression ["Column_Name"]

returns the value from the first row at the given column name

Dataset_Expression [Row_Index]

returns the value from the given row at the first column

Dataset_Expression [Row_Index, "Column_Name"]

returns the value from the given row at the given column name

Dataset_Expression [Row_Index, Column_Index]

returns the value from the given row at the given column index

 

For example, this expression would pull a value out of a Table at row 6 for column "ProductCode":

{Root Container.Table.data}[6, "ProductCode"]

 

Note that you'll often have to convince the expression system that what you're doing is safe. The expression language can't tell what the datatype will be for a given column, so you may have to use a type-casting function to convince the expression language to accept your expression, like this:

toInt({Root Container.Table.data}[6, "ProductCode"])

Functions

The expression language's functions are where much of the real power lies. A function may take various arguments, all of which can themselves be any arbitrary expression. This means that you can use the results of one function as the argument to another function. In general, the syntax for a function call is:

functionName(expression1, expression2, ...)

 

The rest of this user manual section is devoted to the various functions available.

Whitespace and Comments

Whitespace, such as spaces, tabs and newlines, are largely ignored in the expression language. It is often helpful to break your expression up onto multiple lines for clarity. Comments are delimited by two forward slashes. This will make the rest of that line be ignored. This example shows an if function spread over 4 lines with comments annotating the arguments.

if( {Root Container.UseTagValueOption.selected},

    {MyTags/SomeValue}// Use the tag value

    "Not Selected",     // Use default value if the user doesn't check the box

)