Q: How can I extract all the names of an expression? about expr HOT 2 CLOSED

Visitor will help with this. But now it isn’t implemented, so there is no way now of extracting names. But I think this is good feature and if I have time, I’ll implement it.

from expr.

Now it's possible:

ast package provides Visitor interface and BaseVisitor implementation.
You can use it for traveling ast tree of compiled program.

For example if you want to collect all variable names:

import "github.com/antonmedv/expr/ast"

type visitor struct {
	ast.BaseVisitor
	identifiers []string
}

func (v *visitor) IdentifierNode(node *ast.IdentifierNode) {
	v.identifiers = append(v.identifiers, node.Value)
}

program, err := expr.Compile("foo + bar", expr.Env(env))

visitor := &visitor{}
ast.Walk(node, visitor)
	
fmt.Printf("%v", visitor.identifiers) // outputs [foo bar]

from expr.