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eval.go
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eval.go
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// A reflection based evaluation of an AST.
package tick
import (
"fmt"
"reflect"
"regexp"
"runtime"
"strings"
"time"
"unicode"
"unicode/utf8"
)
// Interface for interacting with objects.
// If an object does not self describe via this interface
// than a reflection based implemenation will be used.
type SelfDescriber interface {
//A description the object
Desc() string
HasMethod(name string) bool
CallMethod(name string, args ...interface{}) (interface{}, error)
HasProperty(name string) bool
Property(name string) interface{}
SetProperty(name string, arg interface{}) error
}
// Parse and evaluate a given script for the scope.
// This evaluation method uses reflection to call
// methods on objects within the scope.
func Evaluate(script string, scope *Scope) (err error) {
defer func(errP *error) {
r := recover()
if r == ErrEmptyStack {
trace := make([]byte, 1024)
n := runtime.Stack(trace, false)
*errP = fmt.Errorf("evaluation caused stack error: %v Go Trace: %s", r, string(trace[:n]))
} else if r != nil {
panic(r)
}
}(&err)
root, err := parse(script)
if err != nil {
return err
}
// Use a stack machine to evaluate the AST
stck := &stack{}
return eval(root, scope, stck)
}
// Evaluate a node using a stack machine in a given scope
func eval(n Node, scope *Scope, stck *stack) (err error) {
switch node := n.(type) {
case *BoolNode:
stck.Push(node.Bool)
case *NumberNode:
if node.IsInt {
stck.Push(node.Int64)
} else {
stck.Push(node.Float64)
}
case *DurationNode:
stck.Push(node.Dur)
case *StringNode:
stck.Push(node.Literal)
case *RegexNode:
stck.Push(node.Regex)
case *UnaryNode:
err = eval(node.Node, scope, stck)
if err != nil {
return
}
evalUnary(node.Operator, scope, stck)
case *LambdaNode:
// Catch panic from resolveIdents and return as error.
err = func() (e error) {
defer func(ep *error) {
err := recover()
if err != nil {
*ep = err.(error)
}
}(&e)
node.Node = resolveIdents(node.Node, scope)
return e
}()
if err != nil {
return
}
stck.Push(node.Node)
case *BinaryNode:
err = eval(node.Left, scope, stck)
if err != nil {
return
}
err = eval(node.Right, scope, stck)
if err != nil {
return
}
err = evalBinary(node.Operator, scope, stck)
if err != nil {
return
}
case *FunctionNode:
args := make([]interface{}, len(node.Args))
for i, arg := range node.Args {
err = eval(arg, scope, stck)
if err != nil {
return
}
a := stck.Pop()
switch typed := a.(type) {
case *IdentifierNode:
// Resolve identifier
a, err = scope.Get(typed.Ident)
if err != nil {
return err
}
case unboundFunc:
// Call global func
a, err = typed(nil)
if err != nil {
return err
}
}
args[i] = a
}
err = evalFunc(node, scope, stck, args)
if err != nil {
return
}
case *ListNode:
for _, n := range node.Nodes {
err = eval(n, scope, stck)
if err != nil {
return
}
// Pop unused result
if stck.Len() > 0 {
stck.Pop()
}
}
default:
stck.Push(node)
}
return nil
}
func evalUnary(op tokenType, scope *Scope, stck *stack) error {
v := stck.Pop()
switch op {
case TokenMinus:
switch n := v.(type) {
case float64:
stck.Push(-1 * n)
case int64:
stck.Push(-1 * n)
default:
return fmt.Errorf("invalid arugument to '-' %v", v)
}
case TokenNot:
if b, ok := v.(bool); ok {
stck.Push(!b)
} else {
return fmt.Errorf("invalid arugument to '!' %v", v)
}
}
return nil
}
func evalBinary(op tokenType, scope *Scope, stck *stack) error {
r := stck.Pop()
l := stck.Pop()
switch op {
case TokenAsgn:
i := l.(*IdentifierNode)
scope.Set(i.Ident, r)
case TokenDot:
// Resolve identifier
if left, ok := l.(*IdentifierNode); ok {
var err error
l, err = scope.Get(left.Ident)
if err != nil {
return err
}
}
switch right := r.(type) {
case unboundFunc:
ret, err := right(l)
if err != nil {
return err
}
stck.Push(ret)
case *IdentifierNode:
name := right.Ident
//Lookup field by name of left object
var describer SelfDescriber
if d, ok := l.(SelfDescriber); ok {
describer = d
} else {
describer = NewReflectionDescriber(l)
}
if describer.HasProperty(name) {
stck.Push(describer.Property(name))
} else {
return fmt.Errorf("object %T has no property %s", l, name)
}
default:
return fmt.Errorf("invalid right operand of type %T to '.' operator", r)
}
}
return nil
}
func evalFunc(f *FunctionNode, scope *Scope, stck *stack, args []interface{}) error {
rec := func(obj interface{}, errp *error) {
e := recover()
if e != nil {
*errp = fmt.Errorf("error calling func %q on obj %T: %v", f.Func, obj, e)
if strings.Contains((*errp).Error(), "*tick.ReferenceNode") && strings.Contains((*errp).Error(), "type string") {
*errp = fmt.Errorf("cannot assign *tick.ReferenceNode to type string, did you use double quotes instead of single quotes?")
}
}
}
fnc := unboundFunc(func(obj interface{}) (_ interface{}, err error) {
//Setup recover method if there is a panic during the method call
defer rec(obj, &err)
if obj == nil {
// Object is nil, check for func in scope
fnc, _ := scope.Get(f.Func)
if fnc == nil {
return nil, fmt.Errorf("no global function %q defined", f.Func)
}
method := reflect.ValueOf(fnc)
return callMethodReflection(method, args)
}
// Get SelfDescriber
name := f.Func
var describer SelfDescriber
if d, ok := obj.(SelfDescriber); ok {
describer = d
} else {
describer = NewReflectionDescriber(obj)
}
// Check for Method
if describer.HasMethod(name) {
return describer.CallMethod(name, args...)
}
// Check for dynamic method.
dm := scope.DynamicMethod(name)
if dm != nil {
ret, err := dm(obj, args...)
if err != nil {
return nil, err
}
return ret, nil
}
// Ran out of options...
return nil, fmt.Errorf("No method or property %q on %s", name, describer.Desc())
})
stck.Push(fnc)
return nil
}
// Wraps any object as a SelfDescriber using reflection.
type ReflectionDescriber struct {
obj interface{}
}
func NewReflectionDescriber(obj interface{}) *ReflectionDescriber {
return &ReflectionDescriber{obj: obj}
}
func (r *ReflectionDescriber) Desc() string {
return reflect.TypeOf(r.obj).Name()
}
// Using reflection check if the object has the method or field.
// A field is a valid method because we can set it via reflection too.
func (r *ReflectionDescriber) HasMethod(name string) bool {
name = capilatizeFirst(name)
v := reflect.ValueOf(r.obj)
if !v.IsValid() {
return false
}
if v.MethodByName(name).IsValid() {
return true
}
// Check for a field of the same name,
// we can wrap setting it in a method.
return r.HasProperty(name)
}
func (r *ReflectionDescriber) CallMethod(name string, args ...interface{}) (interface{}, error) {
name = capilatizeFirst(name)
v := reflect.ValueOf(r.obj)
if !v.IsValid() {
return nil, fmt.Errorf("cannot get reflect.ValueOf %T", r.obj)
}
// Check for a method and call it
if method := v.MethodByName(name); method.IsValid() {
return callMethodReflection(method, args)
}
// Check for a field and set it
if len(args) == 1 && r.HasProperty(name) {
err := r.SetProperty(name, args[0])
if err != nil {
return nil, err
}
return r.obj, nil
}
return nil, fmt.Errorf("unknown method or field %s on %T", name, r.obj)
}
// Using reflection check if the object has a field with the property name.
func (r *ReflectionDescriber) HasProperty(name string) bool {
name = capilatizeFirst(name)
v := reflect.Indirect(reflect.ValueOf(r.obj))
if v.Kind() == reflect.Struct {
field := v.FieldByName(name)
return field.IsValid() && field.CanSet()
}
return false
}
func (r *ReflectionDescriber) Property(name string) interface{} {
name = capilatizeFirst(name)
v := reflect.Indirect(reflect.ValueOf(r.obj))
if v.Kind() == reflect.Struct {
field := v.FieldByName(name)
if field.IsValid() {
return field.Interface()
}
}
return nil
}
func (r *ReflectionDescriber) SetProperty(name string, value interface{}) error {
v := reflect.Indirect(reflect.ValueOf(r.obj))
if v.Kind() == reflect.Struct {
field := v.FieldByName(name)
if field.IsValid() && field.CanSet() {
field.Set(reflect.ValueOf(value))
return nil
}
}
return fmt.Errorf("no field %s on %T", name, r.obj)
}
func callMethodReflection(method reflect.Value, args []interface{}) (interface{}, error) {
rargs := make([]reflect.Value, len(args))
for i, arg := range args {
rargs[i] = reflect.ValueOf(arg)
}
ret := method.Call(rargs)
if l := len(ret); l == 1 {
return ret[0].Interface(), nil
} else if l == 2 {
if i := ret[1].Interface(); i != nil {
if err, ok := i.(error); !ok {
return nil, fmt.Errorf("second return value form function must be an 'error', got %T", i)
} else {
return nil, err
}
} else {
return ret[0].Interface(), nil
}
} else {
return nil, fmt.Errorf("functions must return a single value or (interface{}, error)")
}
}
// Capilatizes the first rune in the string
func capilatizeFirst(s string) string {
r, n := utf8.DecodeRuneInString(s)
s = string(unicode.ToUpper(r)) + s[n:]
return s
}
// Resolve all identifiers immediately in the tree with their value from the scope.
// This operation is performed in place.
// Panics if the scope value does not exist or if the value cannot be expressed as a literal.
func resolveIdents(n Node, scope *Scope) Node {
switch node := n.(type) {
case *IdentifierNode:
v, err := scope.Get(node.Ident)
if err != nil {
panic(err)
}
return valueToLiteralNode(node.pos, v)
case *UnaryNode:
node.Node = resolveIdents(node.Node, scope)
case *BinaryNode:
node.Left = resolveIdents(node.Left, scope)
node.Right = resolveIdents(node.Right, scope)
case *FunctionNode:
for i, arg := range node.Args {
node.Args[i] = resolveIdents(arg, scope)
}
case *ListNode:
for i, n := range node.Nodes {
node.Nodes[i] = resolveIdents(n, scope)
}
}
return n
}
// Convert raw value to literal node, for all supported basic types.
func valueToLiteralNode(pos pos, v interface{}) Node {
switch value := v.(type) {
case bool:
return &BoolNode{
pos: pos,
Bool: value,
}
case int64:
return &NumberNode{
pos: pos,
IsInt: true,
Int64: value,
}
case float64:
return &NumberNode{
pos: pos,
IsFloat: true,
Float64: value,
}
case time.Duration:
return &DurationNode{
pos: pos,
Dur: value,
}
case string:
return &StringNode{
pos: pos,
Literal: value,
}
case *regexp.Regexp:
return &RegexNode{
pos: pos,
Regex: value,
}
default:
panic(fmt.Errorf("unsupported literal type %T", v))
}
}