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syntax.go
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syntax.go
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// This file is for statements by syntax form, such as set!
package scheme
import (
"fmt"
)
var (
builtinSyntaxes = Binding{
"actor": NewSyntax(actorSyntax),
"and": NewSyntax(andSyntax),
"begin": NewSyntax(beginSyntax),
"cond": NewSyntax(condSyntax),
"define": NewSyntax(defineSyntax),
"define-macro": NewSyntax(defineMacroSyntax),
"do": NewSyntax(doSyntax),
"if": NewSyntax(ifSyntax),
"lambda": NewSyntax(lambdaSyntax),
"let": NewSyntax(letSyntax),
"let*": NewSyntax(letStarSyntax),
"letrec": NewSyntax(letrecSyntax),
"or": NewSyntax(orSyntax),
"quote": NewSyntax(quoteSyntax),
"set!": NewSyntax(setSyntax),
}
)
type Syntax struct {
ObjectBase
function func(*Syntax, Object) Object
}
func NewSyntax(function func(*Syntax, Object) Object) *Syntax {
return &Syntax{ObjectBase: ObjectBase{parent: nil}, function: function}
}
func (s *Syntax) Invoke(arguments Object) Object {
return s.function(s, arguments)
}
func (s *Syntax) String() string {
return fmt.Sprintf("#<syntax %s>", s.Bounder())
}
func (s *Syntax) isSyntax() bool {
return true
}
func (s *Syntax) malformedError() {
syntaxError("malformed %s: %s", s.Bounder(), s.Bounder().Parent())
}
func (s *Syntax) assertListEqual(arguments Object, length int) {
if !arguments.isList() || arguments.(*Pair).ListLength() != length {
s.malformedError()
}
}
func (s *Syntax) assertListMinimum(arguments Object, minimum int) {
if !arguments.isList() || arguments.(*Pair).ListLength() < minimum {
s.malformedError()
}
}
func (s *Syntax) assertListRange(arguments Object, lengthRange []int) {
if !arguments.isList() {
s.malformedError()
}
for _, length := range lengthRange {
if length == arguments.(*Pair).ListLength() {
return
}
}
s.malformedError()
}
// Returns elements in list object with type assertion (syntax form specific error message)
// Assertion is minimum
func (s *Syntax) elementsMinimum(list Object, minimum int) []Object {
if list.isApplication() {
list = list.(*Application).toList()
}
s.assertListMinimum(list, minimum)
return list.(*Pair).Elements()
}
// Returns elements in list object with type assertion (syntax form specific error message)
// Assertion is equal
func (s *Syntax) elementsExact(list Object, value int) []Object {
if list.isApplication() {
list = list.(*Application).toList()
}
s.assertListEqual(list, value)
return list.(*Pair).Elements()
}
// Eval all given objects and returns last object's eval result.
// When 'objects' is empty, returns #<undef>.
func evalAll(objects []Object) Object {
lastResult := undef
for _, object := range objects {
lastResult = object.Eval()
}
return lastResult
}
func actorSyntax(s *Syntax, arguments Object) Object {
elements := s.elementsMinimum(arguments, 0)
// Insert over the application to override scope
application := arguments.Parent()
actor := NewActor(application.Parent())
application.setParent(actor)
for _, element := range elements {
caseElements := s.elementsMinimum(element, 1)
caseArguments := s.elementsMinimum(caseElements[0], 1)
assertObjectType(caseArguments[0], "string")
actor.functions[caseArguments[0].(*String).text] = func(objects []Object) {
if len(caseArguments[1:]) != len(objects) {
runtimeError("invalid message argument length: requires %d, but got %d", len(caseArguments[1:]), len(objects))
}
for index, variable := range caseArguments[1:] {
actor.tryDefine(variable, objects[index].Eval())
}
evalAll(caseElements[1:])
}
}
return actor
}
func andSyntax(s *Syntax, arguments Object) Object {
s.assertListMinimum(arguments, 0)
lastResult := Object(NewBoolean(true))
for _, object := range arguments.(*Pair).Elements() {
lastResult = object.Eval()
if lastResult.isBoolean() && lastResult.(*Boolean).value == false {
return NewBoolean(false)
}
}
return lastResult
}
func beginSyntax(s *Syntax, arguments Object) Object {
elements := s.elementsMinimum(arguments, 0)
return evalAll(elements)
}
func condSyntax(s *Syntax, arguments Object) Object {
elements := s.elementsMinimum(arguments, 0)
if len(elements) == 0 {
syntaxError("at least one clause is required for cond")
}
// First: syntax check
elseExists := false
for _, element := range elements {
if elseExists {
syntaxError("'else' clause followed by more clauses")
} else if element.isApplication() && element.(*Application).procedure.isVariable() &&
element.(*Application).procedure.(*Variable).identifier == "else" {
elseExists = true
}
if element.isNull() || !element.isApplication() {
syntaxError("bad clause in cond")
}
}
// Second: eval cases
for _, element := range elements {
lastResult := undef
application := element.(*Application)
isElse := application.procedure.isVariable() && application.procedure.(*Variable).identifier == "else"
if !isElse {
lastResult = application.procedure.Eval()
}
// first element is 'else' or not '#f'
if isElse || !lastResult.isBoolean() || lastResult.(*Boolean).value == true {
for _, object := range application.arguments.(*Pair).Elements() {
lastResult = object.Eval()
}
return lastResult
}
}
return undef
}
func defineSyntax(s *Syntax, arguments Object) Object {
elements := s.elementsExact(arguments, 2)
if elements[0].isVariable() {
variable := elements[0].(*Variable)
s.Bounder().define(variable.identifier, elements[1].Eval())
return NewSymbol(variable.identifier)
} else if elements[0].isApplication() {
closure := WrapClosure(arguments)
defineElements := s.elementsMinimum(elements[0], 1)
funcName := defineElements[0]
closure.DefineFunction(s, defineElements[1:], elements[1:])
if funcName.isVariable() {
s.Bounder().define(funcName.(*Variable).identifier, closure)
return funcName
}
}
return syntaxError("%s", s.Bounder().Parent())
}
func defineMacroSyntax(s *Syntax, arguments Object) Object {
elements := s.elementsMinimum(arguments, 2)
macroElements := s.elementsMinimum(elements[0], 1)
assertObjectType(macroElements[0], "variable")
macro := NewMacro()
s.Bounder().define(macroElements[0].(*Variable).identifier, macro)
return undef
}
func doSyntax(s *Syntax, arguments Object) Object {
closure := WrapClosure(arguments.Parent())
// Parse iterator list and define first variable
elements := s.elementsMinimum(arguments, 2)
iteratorBodies := s.elementsMinimum(elements[0], 0)
for _, iteratorBody := range iteratorBodies {
iteratorElements := s.elementsMinimum(iteratorBody, 2)
if len(iteratorElements) > 3 {
compileError("bad update expr in %s: %s", s.Bounder(), s.Bounder().Parent())
}
closure.tryDefine(iteratorElements[0], iteratorElements[1].Eval())
}
// eval test ->
// true: eval testBody and returns its result
// false: eval continueBody, eval iterator's update
testElements := s.elementsMinimum(elements[1], 1)
for {
testResult := testElements[0].Eval()
if !testResult.isBoolean() || testResult.(*Boolean).value == true {
for _, element := range testElements[1:] {
testResult = element.Eval()
}
return testResult
} else {
// eval continueBody
evalAll(elements[2:])
// update iterators
for _, iteratorBody := range iteratorBodies {
iteratorElements := s.elementsMinimum(iteratorBody, 2)
if len(iteratorElements) == 3 {
closure.tryDefine(iteratorElements[0], iteratorElements[2].Eval())
}
}
}
}
return undef
}
func ifSyntax(s *Syntax, arguments Object) Object {
s.assertListRange(arguments, []int{2, 3})
elements := arguments.(*Pair).Elements()
result := elements[0].Eval()
if result.isBoolean() && !result.(*Boolean).value {
if len(elements) == 3 {
return elements[2].Eval()
} else {
return undef
}
} else {
return elements[1].Eval()
}
}
func lambdaSyntax(s *Syntax, arguments Object) Object {
closure := WrapClosure(arguments.Parent())
elements := s.elementsMinimum(arguments, 1)
variables := s.elementsMinimum(elements[0], 0)
closure.DefineFunction(s, variables, elements[1:])
return closure
}
func letSyntax(s *Syntax, arguments Object) Object {
closure := WrapClosure(arguments.Parent())
elements := s.elementsMinimum(arguments, 1)
// define arguments to local scope
variables := []Object{}
results := []Object{}
for _, argumentElement := range s.elementsMinimum(elements[0], 0) {
variableElements := s.elementsExact(argumentElement, 2)
variableElements[1].setParent(closure.Parent())
variables = append(variables, variableElements[0])
results = append(results, variableElements[1].Eval())
}
for index, variable := range variables {
closure.tryDefine(variable, results[index])
}
// eval body
return evalAll(elements[1:])
}
func letStarSyntax(s *Syntax, arguments Object) Object {
closure := WrapClosure(arguments.Parent())
elements := s.elementsMinimum(arguments, 1)
// define arguments to local scope
for _, argumentElement := range s.elementsMinimum(elements[0], 0) {
variableElements := s.elementsExact(argumentElement, 2)
variable, result := variableElements[0], variableElements[1].Eval()
closure.tryDefine(variable, result)
result.setParent(closure.Parent())
}
// eval body
return evalAll(elements[1:])
}
func letrecSyntax(s *Syntax, arguments Object) Object {
closure := WrapClosure(arguments.Parent())
elements := s.elementsMinimum(arguments, 1)
// define arguments to local scope
variables := []Object{}
results := []Object{}
for _, argumentElement := range s.elementsMinimum(elements[0], 0) {
variableElements := s.elementsExact(argumentElement, 2)
variables = append(variables, variableElements[0])
results = append(results, variableElements[1].Eval())
}
for index, variable := range variables {
closure.tryDefine(variable, results[index])
}
// eval body
return evalAll(elements[1:])
}
func orSyntax(s *Syntax, arguments Object) Object {
s.assertListMinimum(arguments, 0)
lastResult := Object(NewBoolean(false))
for _, object := range arguments.(*Pair).Elements() {
lastResult = object.Eval()
if !lastResult.isBoolean() || lastResult.(*Boolean).value != false {
return lastResult
}
}
return lastResult
}
func quoteSyntax(s *Syntax, arguments Object) Object {
s.assertListEqual(arguments, 1)
object := arguments.(*Pair).ElementAt(0)
p := NewParser(object.String())
p.Peek()
return p.parseQuotedObject(s.Bounder())
}
func setSyntax(s *Syntax, arguments Object) Object {
elements := s.elementsExact(arguments, 2)
variable := elements[0]
if !variable.isVariable() {
s.malformedError()
}
value := elements[1].Eval()
s.Bounder().set(variable.(*Variable).identifier, value)
return value
}