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package tengo
// SymbolScope represents a symbol scope.
type SymbolScope string
// List of symbol scopes
const (
ScopeGlobal SymbolScope = "GLOBAL"
ScopeLocal SymbolScope = "LOCAL"
ScopeBuiltin SymbolScope = "BUILTIN"
ScopeFree SymbolScope = "FREE"
)
// Symbol represents a symbol in the symbol table.
type Symbol struct {
Name string
Scope SymbolScope
Index int
LocalAssigned bool // if the local symbol is assigned at least once
}
// SymbolTable represents a symbol table.
type SymbolTable struct {
parent *SymbolTable
block bool
store map[string]*Symbol
numDefinition int
maxDefinition int
freeSymbols []*Symbol
builtinSymbols []*Symbol
}
// NewSymbolTable creates a SymbolTable.
func NewSymbolTable() *SymbolTable {
return &SymbolTable{
store: make(map[string]*Symbol),
}
}
// Define adds a new symbol in the current scope.
func (t *SymbolTable) Define(name string) *Symbol {
symbol := &Symbol{Name: name, Index: t.nextIndex()}
t.numDefinition++
if t.Parent(true) == nil {
symbol.Scope = ScopeGlobal
// if symbol is defined in a block of global scope, symbol index must
// be tracked at the root-level table instead.
if p := t.parent; p != nil {
for p.parent != nil {
p = p.parent
}
t.numDefinition--
p.numDefinition++
}
} else {
symbol.Scope = ScopeLocal
}
t.store[name] = symbol
t.updateMaxDefs(symbol.Index + 1)
return symbol
}
// DefineBuiltin adds a symbol for builtin function.
func (t *SymbolTable) DefineBuiltin(index int, name string) *Symbol {
if t.parent != nil {
return t.parent.DefineBuiltin(index, name)
}
symbol := &Symbol{
Name: name,
Index: index,
Scope: ScopeBuiltin,
}
t.store[name] = symbol
t.builtinSymbols = append(t.builtinSymbols, symbol)
return symbol
}
// Resolve resolves a symbol with a given name.
func (t *SymbolTable) Resolve(
name string,
recur bool,
) (*Symbol, int, bool) {
symbol, ok := t.store[name]
if ok {
// symbol can be used if
if symbol.Scope != ScopeLocal || // it's not of local scope, OR,
symbol.LocalAssigned || // it's assigned at least once, OR,
recur { // it's defined in higher level
return symbol, 0, true
}
}
if t.parent == nil {
return nil, 0, false
}
symbol, depth, ok := t.parent.Resolve(name, true)
if !ok {
return nil, 0, false
}
depth++
// if symbol is defined in parent table and if it's not global/builtin
// then it's free variable.
if !t.block && depth > 0 &&
symbol.Scope != ScopeGlobal &&
symbol.Scope != ScopeBuiltin {
return t.defineFree(symbol), depth, true
}
return symbol, depth, true
}
// Fork creates a new symbol table for a new scope.
func (t *SymbolTable) Fork(block bool) *SymbolTable {
return &SymbolTable{
store: make(map[string]*Symbol),
parent: t,
block: block,
}
}
// Parent returns the outer scope of the current symbol table.
func (t *SymbolTable) Parent(skipBlock bool) *SymbolTable {
if skipBlock && t.block {
return t.parent.Parent(skipBlock)
}
return t.parent
}
// MaxSymbols returns the total number of symbols defined in the scope.
func (t *SymbolTable) MaxSymbols() int {
return t.maxDefinition
}
// FreeSymbols returns free symbols for the scope.
func (t *SymbolTable) FreeSymbols() []*Symbol {
return t.freeSymbols
}
// BuiltinSymbols returns builtin symbols for the scope.
func (t *SymbolTable) BuiltinSymbols() []*Symbol {
if t.parent != nil {
return t.parent.BuiltinSymbols()
}
return t.builtinSymbols
}
// Names returns the name of all the symbols.
func (t *SymbolTable) Names() []string {
var names []string
for name := range t.store {
names = append(names, name)
}
return names
}
func (t *SymbolTable) nextIndex() int {
if t.block {
return t.parent.nextIndex() + t.numDefinition
}
return t.numDefinition
}
func (t *SymbolTable) updateMaxDefs(numDefs int) {
if numDefs > t.maxDefinition {
t.maxDefinition = numDefs
}
if t.block {
t.parent.updateMaxDefs(numDefs)
}
}
func (t *SymbolTable) defineFree(original *Symbol) *Symbol {
// TODO: should we check duplicates?
t.freeSymbols = append(t.freeSymbols, original)
symbol := &Symbol{
Name: original.Name,
Index: len(t.freeSymbols) - 1,
Scope: ScopeFree,
}
t.store[original.Name] = symbol
return symbol
}
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