README.md

Standard Script Engine

The standard script engine is a basic implementation of the script.Engine interface that is used as the default script engine

Supported Operations

operator	name	supported types	description
||	logical OR	boolean	return true if left-side OR right-side are true
&&	logical AND	boolean	return true if left-side AND right-side are true
!	not	boolean	return true if right-side is false. The is no left-side argument
==	equals	number|string	return true if left-side and right-side arguments are equal
!=	not equals	number|string	return true if left-side and right-side arguments are not equal
<=	less than or equal to	number	return true if left-side number is less than or equal to the right-side number
>=	greater than or equal to	number	return true if left-side number is greater than or equal to the right-side number
<	less than	number	return true if left-side number is less than the right-side number
>	greater than	number	return true if left-side number is greater than the right-side number
=~	regex	string	perform a regex match on the left-side value using the right-side pattern
+	plus/addition	number	return the left-side number added to the right-side number
-	minus/subtraction	number	return the left-side number minus the right-side number
**	power	number	return the left-side number increased to the power of the right-side number
*	multiplication	number	return the left-side number multiplied by the right-side number
/	division	number	return the left-side number divided by the right-side number
%	modulus	integer	return the remainder of the left-side number divided by the right-side number
in	in	number|string|boolean and collection	return true if the left-side argument is in the right-side collection
not in	in	number|string|boolean and collection	return true if the left-side argument is not in the right-side collection

All operators have a left-side and right-side argument, expect the not ! operator which only as a right-side argument. The arguments can be strings, numbers, boolean values, arrays, objects, a special parameter, or other expressions, for example true && true || false includes the logical AND operator with left-side true and right-side a logical OR operator with left-side true and right-side false.

Regex

The regex operator will perform a regex match check using the left side argument as the input and the right as the regex pattern.

The right side pattern should be passed as a string, between single or double quotes, to ensure that no characters are mistaken for other operators.

the regex operation is handled by the standard regexp golang library Match function.

In and Not In

The in and not in operators will check if the left-side value, treated either as a number, string, or boolean value, is included in the right-side collection values, a collection can either be an array, slice, or the values of a map.

Special Parameters

The following symbols/tokens have special meaning when used in script expressions and will be replaced before the expression is evaluated. The symbols used within a string, between single or double quotes, will not be replaced.

symbol	name	replacement
$	root	the root json data node
@	current	the current json data node
nil	nil	nil
null	null	nil

Using the root or current symbol allows to embed a JSONPath selector within an expression and it is expected that any argument that includes these characters should be a valid selector.

The nil and null tokens can be used interchangeably to represent a nil value.

remember that the @ character has different meaning in subscripts than it does in filters.

Limitations

The script parser does not infer meaning from symbols/tokens and the neighboring characters, what may be considered a valid mathematical equation is not always a valid script expression.

For example, the equations 8+3-3*6+2(2*3) will not be parsed correctly as the engine does not under stand that 2(2*3) is the same as 2*(2*3), if you needed such an equation you would remove any ambiguity of what a number next to a bracket means like so 8+3-3*6+2*(2*3).