Package eval implements evaluation of GoLang expression at runtime.
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).
- expression itself and all of subexpression must return exactly one value,
- see documentation Bugs section for other requirements/restrictions.
- 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.
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"
Please report bug if you found it.
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