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 any one of the following:

- Number
- Boolean
- String
- Bound Tag
- Bound property
- Function call
- Dataset access
- Equation involving any of these

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 8.456 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" |

In addition, the following escape characters are available:

Character | Description |
---|---|

\n | New line |

\r | Tab |

\t | Carriage return |

// The words "Hello" and "User" will be placed on separate lines "Hello\nUser" // Each "\t" will inject a tab "Lots\tOf\tSpace" |

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

Operator | Name | Description | |
---|---|---|---|

// | Comments | Allows for comments following this operator. | |

- | Unary Minus or Subtraction | If both preceeded by a number, then returns a value by subtracting the operand right from the operand on the left of the operator: If preceded by anything else (or nothing, such as the start of the expression) and is followed by a number, this operator will negate the number.
| |

! | Not | Logical opposite of a boolean. | |

^ | Power | Raises a number to the power of another number. | |

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

* | Multiply | Multiplies the number on the left of the operator by the number on the right of the operator. | |

/ | Divide | Divides the number on the left of the operator by the number on the right of the operator. | |

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

- | Subtraction | Subtracts the number on the right of the operator from the number on the left of the operator. | |

~ | Bitwise NOT | Examples the bits of an operand, and performs performs logical negation: bits with a value of 0 become 1, and vice versa. | |

& | Bitwise AND | Examines the bits of two operands, and performs a logical AND to each set, comparing the bits in each position from both sets. Returns true for any position where the bits being compared are true.
| |

| | Bitwise OR | Examines the bits of two operands, and performs a logical OR to each set, comparing the bits in each position from both sets. Returns true for any position where either bit being compared is true.
| |

xor | Bitwise XOR | Examines the bits of two operands, and performs a logical exclusive OR to each set, comparing the bits in each position from both sets. Returns true for any position where only one of the bits are true.
| |

<< | 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 | Logical less-than test between two numbers. Returns a boolean. | |

>= | Greater Than or Equal To | Tests if the operand on the left is greater or equal to the operand on the right. Returns a boolean. | |

<= | Less Than or Equal To | Tests if the operand on the left is less than or equal to the operand on the right. Returns a boolean. | |

= | 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 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 in Vision, 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** icon and **Insert Tag** icon to build these references for you.

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 [Column_Index] //returns the value from the given column at the first row 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"]) |

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, ...) |

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 ) |

While referencing a tag path in expressions, you may see some special notation, such as "~" and "[.]". More information on this notation can be found on the Understanding Tags page.