BoolExpr

A Go package to evaluate boolean expressions. against a map of variables. variables can be lazy computed using a function that return the value.

BoolExpr allows your program user to write a bool expression in the form: x = 10 and y > 20 and z = "hello" and then run it many times against functions: x,y,z which returns int, int, string values. the evaluation returns a simple bool

Usage

You can parse and evaluate the expression in one call

exp := `x = 10 and y >= 20 and z = "hello"`
var symbols SymbolsMap = map[string]any{
    "x": func() any { return 10 },
    "y": 30,
    "z": func() string { return "hello" },
}
output, err := Eval(exp, symbols) // Output: true, nil

or you can parse and evaulate multiple times

exp := `x = 10 and y >= 20 and z = "hello"`
ast, err := Parse(exp)

var symbols SymbolsMap = map[string]any{
    "x": func() any { return 10 },
    "y": func() any { return 30 },
    "z": func() any { return "hello" },
}
output, err := EvalBoolExpr(ast, symbols) // Output: true, nil

symbols = map[string]func() any{
    "x": func() any { return 0 },
    "y": func() any { return 30 },
    "z": func() any { return "hello" },
}
output, err = EvalBoolExpr(ast, symbols) // Output: false, nil

Syntax

The syntax supports:

The following comparisons: =, !=, >, <, >=, <=
And the logical operators: and, or
And the values types: int, float, string, bool
logical expressions can be grouped with (...)
The comparison must always be in the form value operator value
- value can be a symbol or a literal e.g x, 1, true, "hello"
- operator is one of the comparison operators Symbols map is a map from string (the variable name) to any value:
If the value is a literal (string, int, float, bool) it'll be used
If it's a func() string/int/float/bool it'll be evaluated and the return value will be used
If it's a func() any it'll be also evaluated and the return value used.
If it's a func() (string/int/float/bool, error) the value returned will be used if no error. If an error is returned the evaluation is terminated and the error is returned.

Expressions examples:

x > 1
x > y and y > z
x = 10 and y != 20
x > 10 and y < 20 or z = true
x != 20 or y = 30 or z = "helloworld" or (a = false and b = true)

Evaluation

BoolExpr will short circuit in two situations:

If and is used and the left operand is false, the right operand will not be executed and it'll return false
If or is used and the left operand is true, the right opreand will not be executed and it'll return true

Examples