add scopes

This commit is contained in:
David 2021-09-19 14:46:00 -04:00
parent b1cd274a39
commit e4f2519891
7 changed files with 136 additions and 9 deletions

View File

@ -33,6 +33,11 @@ class ASTPrinter implements Expr.Visitor<String> {
return expr.name.toString();
}
@Override
public String visitAssignExpr(Expr.Assign expr) {
return expr.name.toString();
}
private String parenthesize(String name, Expr... exprs) {
StringBuilder builder = new StringBuilder();

View File

@ -4,16 +4,44 @@ import java.util.HashMap;
import java.util.Map;
class Environment {
final Environment enclosing;
private final Map<String, Object> values = new HashMap<>();
Environment() {
enclosing = null;
}
Environment(Environment enclosing) {
this.enclosing = enclosing;
}
void define(String name, Object value) {
values.put(name, value);
}
void assign(Token name, Object value) {
if (values.containsKey(name.lexeme)) {
values.put(name.lexeme, value);
return;
}
if (enclosing != null) {
enclosing.assign(name, value);
return;
}
throw new RuntimeError(name, "Undefined variable '" + name.lexeme + "'.");
}
Object get(Token name) {
if (values.containsKey(name.lexeme)) {
return values.get(name.lexeme);
}
if (enclosing != null) {
return enclosing.get(name);
}
throw new RuntimeError(name, "Undefined variable '" + name.lexeme + "'.");
}
}

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@ -1,7 +1,10 @@
package lox;
import java.util.List;
abstract class Expr {
interface Visitor<R> {
R visitAssignExpr(Assign expr);
R visitBinaryExpr(Binary expr);
R visitGroupingExpr(Grouping expr);
R visitLiteralExpr(Literal expr);
@ -9,6 +12,21 @@ abstract class Expr {
R visitVariableExpr(Variable expr);
}
static class Assign extends Expr {
Assign(Token name, Expr value) {
this.name = name;
this.value = value;
}
@Override
<R> R accept(Visitor<R> visitor) {
return visitor.visitAssignExpr(this);
}
final Token name;
final Expr value;
}
static class Binary extends Expr {
Binary(Expr left, Token operator, Expr right) {
this.left = left;

View File

@ -89,6 +89,13 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
return environment.get(expr.name);
}
@Override
public Object visitAssignExpr(Expr.Assign expr) {
Object value = evaluate(expr.value);
environment.assign(expr.name, value);
return value;
}
@Override
public Void visitExpressionStmt(Stmt.Expression stmt) {
evaluate(stmt.expression);
@ -112,6 +119,12 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
return null;
}
@Override
public Void visitBlockStmt(Stmt.Block stmt) {
executeBlock(stmt.statements, new Environment(environment));
return null;
}
private void checkNumberOperand(Token operator, Object operand) {
if (operand instanceof Double) {
return;
@ -167,4 +180,18 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
private void execute(Stmt stmt) {
stmt.accept(this);
}
void executeBlock(List<Stmt> statements, Environment environment) {
Environment previous = this.environment;
try {
this.environment = environment;
for (Stmt statement : statements) {
// could also just redesign this to accept an environment field everywhere
execute(statement);
}
} finally {
this.environment = previous;
}
}
}

View File

@ -50,6 +50,9 @@ class Parser {
if (match(PRINT)) {
return printStatement();
}
if (match(LEFT_BRACE)) {
return new Stmt.Block(block());
}
return expressionStatement();
}
@ -65,8 +68,35 @@ class Parser {
return new Stmt.Expression(value);
}
private List<Stmt> block() {
List<Stmt> statements = new ArrayList<>();
while (!check(RIGHT_BRACE) && !isAtEnd()) {
statements.add(declaration());
}
consume(RIGHT_BRACE, "Expect '}' after block.");
return statements;
}
private Expr assignment() {
Expr expr = equality();
if (match(EQUAL)) {
Token equals = previous();
Expr value = assignment();
if (expr instanceof Expr.Variable) {
Token name = ((Expr.Variable)expr).name;
return new Expr.Assign(name, value);
}
// does not throw because parsing _can_ continue
error(equals, "Invalid assignment target.");
}
return expr;
}
private Expr expression() {
return equality();
return assignment();
}
private Expr equality() {

View File

@ -1,12 +1,28 @@
package lox;
import java.util.List;
abstract class Stmt {
interface Visitor<R> {
R visitBlockStmt(Block stmt);
R visitExpressionStmt(Expression stmt);
R visitVarStmt(Var stmt);
R visitPrintStmt(Print stmt);
}
static class Block extends Stmt {
Block(List<Stmt> statements) {
this.statements = statements;
}
@Override
<R> R accept(Visitor<R> visitor) {
return visitor.visitBlockStmt(this);
}
final List<Stmt> statements;
}
static class Expression extends Stmt {
Expression(Expr expression) {
this.expression = expression;

View File

@ -1,5 +1,6 @@
package tool;
import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.nio.charset.Charset;
@ -17,6 +18,7 @@ public class GenerateAST {
outputDir,
"Expr",
Arrays.asList(
"Assign : Token name, Expr value",
"Binary : Expr left, Token operator, Expr right",
"Grouping : Expr expression",
"Literal : Object value",
@ -27,6 +29,7 @@ public class GenerateAST {
outputDir,
"Stmt",
Arrays.asList(
"Block : List<Stmt> statements",
"Expression : Expr expression",
"Var : Token name, Expr initializer",
"Print : Expr expression"));
@ -34,13 +37,13 @@ public class GenerateAST {
private static void defineAST(String outputDir, String baseName, List<String> types)
throws IOException {
String path = outputDir + "/" + baseName + ".java";
String path = outputDir + File.separator + baseName + ".java";
PrintWriter writer = new PrintWriter(path, Charset.defaultCharset());
writer.println("package lox;");
writer.println();
// writer.println("import java.util.List;");
// writer.println();
writer.println("import java.util.List;");
writer.println();
writer.println("abstract class " + baseName + " {");
defineVisitor(writer, baseName, types);