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Environment.java
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Environment.java
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//> Statements and State environment-class
package com.craftinginterpreters.lox;
import java.util.HashMap;
import java.util.Map;
class Environment {
//> enclosing-field
final Environment enclosing;
//< enclosing-field
private final Map<String, Object> values = new HashMap<>();
//> environment-constructors
Environment() {
enclosing = null;
}
Environment(Environment enclosing) {
this.enclosing = enclosing;
}
//< environment-constructors
//> environment-get
Object get(Token name) {
if (values.containsKey(name.lexeme)) {
return values.get(name.lexeme);
}
//> environment-get-enclosing
if (enclosing != null) return enclosing.get(name);
//< environment-get-enclosing
throw new RuntimeError(name,
"Undefined variable '" + name.lexeme + "'.");
}
//< environment-get
//> environment-assign
void assign(Token name, Object value) {
if (values.containsKey(name.lexeme)) {
values.put(name.lexeme, value);
return;
}
//> environment-assign-enclosing
if (enclosing != null) {
enclosing.assign(name, value);
return;
}
//< environment-assign-enclosing
throw new RuntimeError(name,
"Undefined variable '" + name.lexeme + "'.");
}
//< environment-assign
//> environment-define
void define(String name, Object value) {
values.put(name, value);
}
//< environment-define
//> Resolving and Binding ancestor
Environment ancestor(int distance) {
Environment environment = this;
for (int i = 0; i < distance; i++) {
environment = environment.enclosing; // [coupled]
}
return environment;
}
//< Resolving and Binding ancestor
//> Resolving and Binding get-at
Object getAt(int distance, String name) {
return ancestor(distance).values.get(name);
}
//< Resolving and Binding get-at
//> Resolving and Binding assign-at
void assignAt(int distance, Token name, Object value) {
ancestor(distance).values.put(name.lexeme, value);
}
//< Resolving and Binding assign-at
//> omit
@Override
public String toString() {
String result = values.toString();
if (enclosing != null) {
result += " -> " + enclosing.toString();
}
return result;
}
//< omit
}