/
Interpreter.swift
330 lines (284 loc) · 11.5 KB
/
Interpreter.swift
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//
// Interpreter.swift
// slox
//
// Created by Danielle Kefford on 2/26/24.
//
import Foundation
class Interpreter {
var environment: Environment = Environment()
init() {
setUpGlobals()
}
private func setUpGlobals() {
let clock = LoxFunction(name: "clock",
arity: 0,
function: { _, _ -> LoxValue in
return .number(Date().timeIntervalSince1970)
})
environment.define(name: "clock", value: .function(clock))
}
func interpret(statements: [Statement]) throws {
for statement in statements {
try execute(statement: statement)
}
}
func interpretRepl(statements: [Statement]) throws -> LoxValue? {
var result: LoxValue? = nil
for (i, statement) in statements.enumerated() {
if i == statements.endIndex-1, case .expression(let expr) = statement {
result = try evaluate(expr: expr)
} else {
do {
try execute(statement: statement)
} catch Return.return(let value) {
result = value
}
}
}
return result
}
private func execute(statement: Statement) throws {
switch statement {
case .expression(let expr):
let _ = try evaluate(expr: expr)
case .if(let testExpr, let consequentStmt, let alternativeStmt):
try handleIfStatement(testExpr: testExpr,
consequentStmt: consequentStmt,
alternativeStmt: alternativeStmt)
case .print(let expr):
try handlePrintStatement(expr: expr)
case .variableDeclaration(let name, let expr):
try handleVariableDeclaration(name: name, expr: expr)
case .block(let statements):
try handleBlock(statements: statements,
environment: Environment(enclosingEnvironment: environment))
case .while(let expr, let stmt):
try handleWhileStatement(expr: expr, stmt: stmt)
case .function(let name, let lambda):
try handleFunctionDeclaration(name: name, lambda: lambda)
case .return(let returnToken, let expr):
try handleReturnStatement(returnToken: returnToken, expr: expr)
}
}
private func handleIfStatement(testExpr: Expression,
consequentStmt: Statement,
alternativeStmt: Statement?) throws {
if isTruthy(value: try evaluate(expr: testExpr)) {
try execute(statement: consequentStmt)
} else if let alternativeStmt {
try execute(statement: alternativeStmt)
}
}
private func handlePrintStatement(expr: Expression) throws {
let literal = try evaluate(expr: expr)
print(literal)
}
private func handleFunctionDeclaration(name: Token, lambda: Expression) throws {
guard case .lambda(let params, let body) = lambda else {
throw RuntimeError.notALambda
}
let function = LoxFunction(name: name.lexeme, arity: params.count, function: { (interpreter, args) in
let environment = interpreter.environment
for (i, arg) in args.enumerated() {
environment.define(name: params[i].lexeme, value: arg)
}
do {
try interpreter.handleBlock(statements: body, environment: environment)
} catch Return.return(let value) {
return value
}
return .nil
})
environment.define(name: name.lexeme, value: .function(function))
}
private func handleReturnStatement(returnToken: Token, expr: Expression?) throws {
var value: LoxValue = .nil
if let expr {
value = try evaluate(expr: expr)
}
throw Return.return(value)
}
private func handleVariableDeclaration(name: Token, expr: Expression?) throws {
var value: LoxValue = .nil
if let expr = expr {
value = try evaluate(expr: expr)
}
environment.define(name: name.lexeme, value: value)
}
func handleBlock(statements: [Statement], environment: Environment) throws {
let environmentBeforeBlock = self.environment
self.environment = environment
for statement in statements {
try execute(statement: statement)
}
self.environment = environmentBeforeBlock
}
private func handleWhileStatement(expr: Expression, stmt: Statement) throws {
while isTruthy(value: try evaluate(expr: expr)) {
try execute(statement: stmt)
}
}
private func evaluate(expr: Expression) throws -> LoxValue {
switch expr {
case .literal(let literal):
return literal
case .grouping(let expr):
return try evaluate(expr: expr)
case .unary(let oper, let expr):
return try handleUnaryExpression(oper: oper, expr: expr)
case .binary(let leftExpr, let oper, let rightExpr):
return try handleBinaryExpression(leftExpr: leftExpr, oper: oper, rightExpr: rightExpr)
case .variable(let varToken):
return try environment.getValue(name: varToken.lexeme)
case .assignment(let varToken, let valueExpr):
return try handleAssignmentExpression(name: varToken, expr: valueExpr)
case .logical(let leftExpr, let oper, let rightExpr):
return try handleLogicalExpression(leftExpr: leftExpr, oper: oper, rightExpr: rightExpr)
case .call(let calleeExpr, let rightParen, let args):
return try handleFunctionCallExpression(calleeExpr: calleeExpr, rightParen: rightParen, args: args)
case .lambda(let params, let statements):
return try handleLambdaExpression(params: params, statements: statements)
}
}
private func handleUnaryExpression(oper: Token, expr: Expression) throws -> LoxValue {
let value = try evaluate(expr: expr)
switch oper.type {
case .minus:
guard case .number(let number) = value else {
throw RuntimeError.unaryOperandMustBeNumber
}
return .number(-number)
case .bang:
return .boolean(!isTruthy(value: value))
default:
throw RuntimeError.unsupportedUnaryOperator
}
}
private func handleBinaryExpression(leftExpr: Expression,
oper: Token,
rightExpr: Expression) throws -> LoxValue {
let leftValue = try evaluate(expr: leftExpr)
let rightValue = try evaluate(expr: rightExpr)
if case .number(let leftNumber) = leftValue,
case .number(let rightNumber) = rightValue {
switch oper.type {
case .plus:
return .number(leftNumber + rightNumber)
case .minus:
return .number(leftNumber - rightNumber)
case .star:
return .number(leftNumber * rightNumber)
case .slash:
return .number(leftNumber / rightNumber)
case .greater:
return .boolean(leftNumber > rightNumber)
case .greaterEqual:
return .boolean(leftNumber >= rightNumber)
case .less:
return .boolean(leftNumber < rightNumber)
case .lessEqual:
return .boolean(leftNumber <= rightNumber)
default:
break
}
}
if case .string(let leftString) = leftValue,
case .string(let rightString) = rightValue,
case .plus = oper.type {
return .string(leftString + rightString)
}
switch oper.type {
case .bangEqual:
return .boolean(!isEqual(leftValue: leftValue, rightValue: rightValue))
case .equalEqual:
return .boolean(isEqual(leftValue: leftValue, rightValue: rightValue))
case .plus:
throw RuntimeError.binaryOperandsMustBeNumbersOrStrings
case .minus, .star, .slash, .greater, .greaterEqual, .less, .lessEqual:
throw RuntimeError.binaryOperandsMustBeNumbers
default:
throw RuntimeError.unsupportedBinaryOperator
}
}
private func handleAssignmentExpression(name: Token, expr: Expression) throws -> LoxValue {
let value = try evaluate(expr: expr)
try environment.assign(name: name.lexeme, value: value)
return value
}
private func handleLogicalExpression(leftExpr: Expression,
oper: Token,
rightExpr: Expression) throws -> LoxValue {
let leftValue = try evaluate(expr: leftExpr)
if case .and = oper.type {
if !isTruthy(value: leftValue) {
return leftValue
} else {
return try evaluate(expr: rightExpr)
}
} else {
if isTruthy(value: leftValue) {
return leftValue
} else {
return try evaluate(expr: rightExpr)
}
}
}
private func handleFunctionCallExpression(calleeExpr: Expression,
rightParen: Token,
args: [Expression]) throws -> LoxValue {
let callee = try evaluate(expr: calleeExpr)
guard case .function(let actualFunction) = callee else {
throw RuntimeError.notAFunction
}
guard args.count == actualFunction.arity else {
throw RuntimeError.wrongArity(actualFunction.arity, args.count)
}
var argValues: [LoxValue] = []
for arg in args {
let argValue = try evaluate(expr: arg)
argValues.append(argValue)
}
return try actualFunction.call(interpreter: self, args: argValues)
}
private func handleLambdaExpression(params: [Token], statements: [Statement]) throws -> LoxValue {
let function = LoxFunction(name: "<lambda>", arity: params.count, function: { (interpreter, args) in
let environment = interpreter.environment
for (i, arg) in args.enumerated() {
environment.define(name: params[i].lexeme, value: arg)
}
do {
try interpreter.handleBlock(statements: statements, environment: environment)
} catch Return.return(let value) {
return value
}
return .nil
})
return .function(function)
}
private func isEqual(leftValue: LoxValue, rightValue: LoxValue) -> Bool {
switch (leftValue, rightValue) {
case (.nil, .nil):
return true
case (.number(let leftNumber), .number(let rightNumber)):
return leftNumber == rightNumber
case (.string(let leftString), .string(let rightString)):
return leftString == rightString
case (.boolean(let leftBoolean), .boolean(let rightBoolean)):
return leftBoolean == rightBoolean
default:
return false
}
}
// In Lox, `false` and `nil` are false; everything else is true
private func isTruthy(value: LoxValue) -> Bool {
switch value {
case .nil:
return false
case .boolean(let boolean):
return boolean
default:
return true
}
}
}