Binary Expression Tree

Package exp implements a binary expression tree which can be used to evaluate arbitrary binary expressions. You can use this package to build your own expressions however a few expressions are provided out of the box.

Installation

$ go get github.com/alexkappa/exp/...

Usage

Expressions can be used as a rule evaluation engine, where rules are created and evaluated against a target object. A simple example is checking whether a value falls under a pre-defined threshold. We could use an expression to create the rule.

condition := exp.LessThan("value", 10.0)

if condition.Eval(exp.Map{"value": 9.99}) {
	alert.Dispatch()
}

exp.True.Eval(nil)                     // true
exp.False.Eval(nil)                    // false
exp.Not(exp.False).Eval(nil)           // true
exp.Or(exp.True, exp.False).Eval(nil)  // true
exp.And(exp.True, exp.False).Eval(nil) // false

exp.And(
	exp.LessThan("value", 10)
	exp.GreaterThan("value", 5)
).Eval(
	exp.Map{"value": 7}
) // true

It is also possible to use text to describe expressions.

Warning this feature is not battle-tested so use it with caution.

x, err := exp.Parse(`(foo >= 100.00)`)
if err != nil {
	// handle error
}
x.Eval(exp.Map{"foo": "150.00"}) // true

At this time, the following operators are supported. More data types and operators will be added in the future.

Expression	Operator	Data Type
true	True	bool
false	False	false
(true && true)	And	any
(false || true)	Or	any
foo == "xxx"	Match	string
foo != "xxx"	Not(Match)	string
foo == 123	Equal, Eq	float64
foo != 123	NotEqual, Neq	float64
foo > 123	GreaterThan , Gt	float64
foo >= 123	GreaterThanEqual , Gte	float64
foo < 123	LessThan , Lt	float64
foo <= 123	LessThanEqual , Lte	float64