lexpr/README.md

Lexpr - universal expression evaluator

This library can evaluate any types of expressions: math expression, logic expression, simple DSLs.

Installation

go get go.neonxp.dev/lexpr

Usage

ctx := context.Background()
l := lexpr.New(lexpr.WithDefaults())

// Simple math
result1 := <-l.Eval(ctx, `2 + 2 * 2`) // Output channel can return many results
log.Println("Result 1:", result1.Value) // Output: 6

// Helper for exact one result
result2, err := l.OneResult(ctx, `len("test") + 10`)
if err != nil {
 log.Fatal(err)
}
log.Println("Result 2:", result2) // Output: 14

// Custom functions
l.SetFunction("add", func(ts *lexpr.TokenStack) error {
 a, okA := ts.Pop().Number() // first func argument
 b, okB := ts.Pop().Number() // second func argument
 if !okA || !okB {
  return fmt.Errorf("Both args must be number")
 }
 ts.Push(lexpr.TokenFromInt(a + b))
 return nil
})
result3, err := l.OneResult(ctx, `add(12, 24) * 2`)
if err != nil {
 log.Fatal(err)
}
log.Println("Result 3:", result3) // Output: 72

// JSON extraction via dots and variables
jsonString := `{
 "rootKey1": "value1",
 "rootKey2": {
  "childKey1": "value2",
  "childKey2": "value3"
 },
 "arrayKey": [
  "array value 1",
  "array value 2",
  "array value 3",
  "array value 4"
 ]
}`
key1name := "rootKey1"
l.SetVariable("jsonData", jsonString)
l.SetVariable("key1name", key1name)
result41, err := l.OneResult(ctx, `jsonData.key1name`)
if err != nil {
 log.Fatal(err)
}
log.Println("Result 4-1:", result41) // Output: "value1"
result42, err := l.OneResult(ctx, `jsonData.rootKey2.childKey2`)
if err != nil {
 log.Fatal(err)
}
log.Println("Result 4-2:", result42) // Output: "value3"
result43, err := l.OneResult(ctx, `jsonData.arrayKey.3`)
if err != nil {
 log.Fatal(err)
}
log.Println("Result 4-3:", result43) // Output: "array value 4"

// Logic expressions
result51, err := l.OneResult(ctx, `jsonData.key1name == "value1"`)
if err != nil {
 log.Fatal(err)
}
log.Println("Result 5-1:", result51) // Output: 1
result52, err := l.OneResult(ctx, `10 >= 5 || 10 <= 5`)
if err != nil {
 log.Fatal(err)
}
log.Println("Result 5-2:", result52) // Output: 1
result53, err := l.OneResult(ctx, `10 >= 5 && 10 <= 5`)
if err != nil {
 log.Fatal(err)
}
log.Println("Result 5-3:", result53) // Output: 0

Default operators

Operator	Description	Example
	JSON operators
.	Extract field from json	jsonData.key1.0.key2
	Math operators
**	Power number	3 ** 3 = 27
*	Multiple numbers	2 * 4 = 8
/	Divide number	6 / 3 = 2
%	Rem of division	5 % 3 = 2
+	Sum	2 + 2 = 4
-	Substract	6 - 2 = 4
	Logic operators
!	Logic not	!1 = 0
>	More	3 > 2 = 1
>=	More or equal	3 >= 3 = 1
<	Less	3 < 2 = 0
<=	Less or equal	3 <= 3 = 1
==	Equal	1==1 = 1
!=	Not equal	1!=1 = 0
&&	Logic and	3 > 0 && 1 > 0 = 1
`		`

Default functions

Function	Description	Example
max	returns max of two values	max(1,2) = 2
min	returns min of two values	max(1,2) = 1
len	returns length of string	len("test") = 4
atoi	converts string to number	atoi("123") = 123
itoa	converts number to string	itoa(123) = "123"

Contribution

PRs are welcome.