github.com/apaxa-go/eval

eval

Package eval implements evaluation of GoLang expression at runtime.

THIS LIB NO MORE MAINTAINED!

For whose who wants to implement golang eval

Suggestions:

• Implement 2-steps algorithm: first step - analogue of golang compilation (resolve all types; compute all constants; convert all untyped constant and untyped variables to typed; also simplify AST tree here / convert to your own format), second step - analogue of golang runtime (here will be passed values of external variables and computed final result).
• You need to use golang eval package, but keep in mind that it can simplify break your lib on update (golang's backward compatibility does not save you).
• Follow language specification (it is hard to implement some additional custom behaviour without breaking compatibility with language accepted expressions).
• Language specification may omit some details (so also test with golang compiler).

Requirements for expression:

• expression itself and all of subexpression must return exactly one value,
• see documentation Bugs section for other requirements/restrictions.

What does supported:

• types (by passing predefined/custom types and by defining unnamed types in expression itself),
• named arguments (regular variables, typed & untyped constants, untyped boolean variable),
• "package.SomeThing" notation,
• evaluate expression as if it is evaluates in specified package (even write access to private fields),
• evaluate expression like Go evaluates it (following most of specification rules),
• position of error in source on evaluation.

Examples:

Simple:

src:="int8(1*(1+2))"
expr,err:=ParseString(src,"")
if err!=nil{
	return err
}
r,err:=expr.EvalToInterface(nil)
if err!=nil{
	return err
}
fmt.Printf("%v %T", r, r)	// "3 int8"

Complicated:

type exampleString string

func (s exampleString) String() exampleString { return "!" + s + "!" }

type exampleStruct struct {
	A, B int
}

func (s exampleStruct) Sum() int { return s.A + s.B }

func main(){
	c := make(chan int64, 10)
	c <- 2

	src := `exampleString(fmt.Sprint(interface{}(math.MaxInt64/exampleStruct(struct{ A, B int }{3, 5}).Sum()+int(<-(<-chan int64)(c))-cap(make([]string, 1, 100))))).String().String() + "."`

	expr, err := ParseString(src, "")
	if err != nil {
		return
	}
	a := Args{
		"exampleString": MakeTypeInterface(exampleString("")),
		"fmt.Sprint":    MakeDataRegularInterface(fmt.Sprint),
		"math.MaxInt64": MakeDataUntypedConst(constanth.MakeUint(math.MaxInt64)),
		"exampleStruct": MakeTypeInterface(exampleStruct{}),
		"c":             MakeDataRegularInterface(c),
	}
	r, err := expr.EvalToInterface(a)
	if err != nil {
		return
	}
	if r != testR {
		return
	}
	fmt.Printf("%v %T\n", r, r)	// "!!1152921504606846877!!. exampleString"
	return
}

With error:

src := `exampleString(fmt.Sprint(interface{}(math.MaxInt64/exampleStruct(struct{ A, B int }{3, 5}).Sum()+int(<-(<-chan int64)(c))-cap(make([]string, 1, 100))))).String().String() + "."`
expr, err := ParseString(src, "")
if err != nil {
	t.Error(err)
}
a := Args{
	"exampleString": MakeTypeInterface(exampleString("")),
	"fmt.Sprint":    MakeDataRegularInterface(fmt.Sprint),
	"math.MaxInt64": MakeDataUntypedConst(constanth.MakeUint(math.MaxInt64)),
	"exampleStruct": MakeTypeInterface(exampleStruct{}),
	// Remove "c" from passed arguments:
	// "c":             MakeDataRegularInterface(c),
}
_, err = expr.EvalToInterface(a)
fmt.Println(err)	// "expression:1:119: undefined: c"

Bugs

Please report bug if you found it.