From 4a71c219b5fa8e9e28af43925284f429092ba68e Mon Sep 17 00:00:00 2001
From: Tom Willemse
Date: Sun, 31 Jan 2021 17:11:47 -0800
Subject: Add function calls

---
 src/com/craftinginterpreters/lox/CMakeLists.txt    |  2 +-
 src/com/craftinginterpreters/lox/Interpreter.java  | 30 ++++++++++++++++++--
 src/com/craftinginterpreters/lox/LoxFunction.java  | 33 ++++++++++++++++++++++
 src/com/craftinginterpreters/lox/Parser.java       | 22 +++++++++++++++
 src/com/craftinginterpreters/tool/GenerateAst.java |  1 +
 5 files changed, 84 insertions(+), 4 deletions(-)
 create mode 100644 src/com/craftinginterpreters/lox/LoxFunction.java

diff --git a/src/com/craftinginterpreters/lox/CMakeLists.txt b/src/com/craftinginterpreters/lox/CMakeLists.txt
index b437b7a..a068037 100644
--- a/src/com/craftinginterpreters/lox/CMakeLists.txt
+++ b/src/com/craftinginterpreters/lox/CMakeLists.txt
@@ -15,10 +15,10 @@ add_jar(Lox
   Token.java
   Scanner.java
   ${GENERATED_JAVA_FILENAMES}
-  AstPrinter.java
   Parser.java
   Interpreter.java
   RuntimeError.java
   Environment.java
   LoxCallable.java
+  LoxFunction.java
   ENTRY_POINT com/craftinginterpreters/lox/Lox)
diff --git a/src/com/craftinginterpreters/lox/Interpreter.java b/src/com/craftinginterpreters/lox/Interpreter.java
index f752e77..407c537 100644
--- a/src/com/craftinginterpreters/lox/Interpreter.java
+++ b/src/com/craftinginterpreters/lox/Interpreter.java
@@ -4,7 +4,23 @@ import java.util.ArrayList;
 import java.util.List;
 
 class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
-    private Environment environment = new Environment();
+    final Environment globals = new Environment();
+    private Environment environment = globals;
+
+    Interpreter() {
+        globals.define("clock", new LoxCallable() {
+                @Override
+                public int arity() { return 0; }
+
+                @Override
+                public Object call(Interpreter interpreter, List<Object> arguments) {
+                    return (double)System.currentTimeMillis() / 1000.0;
+                }
+
+                @Override
+                public String toString() { return "<native fn>"; }
+            });
+    }
 
     @Override
     public Object visitLiteralExpr(Expr.Literal expr) {
@@ -105,7 +121,7 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
         stmt.accept(this);
     }
 
-    private void executeBlock(List<Stmt> statements, Environment environment) {
+    public void executeBlock(List<Stmt> statements, Environment environment) {
         Environment previous = this.environment;
 
         try {
@@ -131,6 +147,13 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
         return null;
     }
 
+    @Override
+    public Void visitFunctionStmt(Stmt.Function stmt) {
+        LoxFunction function = new LoxFunction(stmt);
+        environment.define(stmt.name.lexeme, function);
+        return null;
+    }
+
     @Override
     public Void visitIfStmt(Stmt.If stmt) {
         if (isTruthy(evaluate(stmt.condition))) {
@@ -238,7 +261,8 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
 
         LoxCallable function = (LoxCallable) callee;
         if (arguments.size() != function.arity()) {
-            throw new RuntimeError(expr.paren, "Expected " + function.arity() + " arguments but got " + arguments.size() + ".");
+            throw new RuntimeError(expr.paren,
+                    "Expected " + function.arity() + " arguments but got " + arguments.size() + ".");
         }
 
         return function.call(this, arguments);
diff --git a/src/com/craftinginterpreters/lox/LoxFunction.java b/src/com/craftinginterpreters/lox/LoxFunction.java
new file mode 100644
index 0000000..d2e367b
--- /dev/null
+++ b/src/com/craftinginterpreters/lox/LoxFunction.java
@@ -0,0 +1,33 @@
+package com.craftinginterpreters.lox;
+
+import java.util.List;
+
+class LoxFunction implements LoxCallable {
+    private final Stmt.Function declaration;
+
+    LoxFunction(Stmt.Function declaration) {
+        this.declaration = declaration;
+    }
+
+    @Override
+    public int arity() {
+        return declaration.params.size();
+    }
+
+    @Override
+    public Object call(Interpreter interpreter, List<Object> arguments) {
+        Environment environment = new Environment(interpreter.globals);
+
+        for (int i = 0; i < declaration.params.size(); i++) {
+            environment.define(declaration.params.get(i).lexeme, arguments.get(i));
+        }
+
+        interpreter.executeBlock(declaration.body, environment);
+        return null;
+    }
+
+    @Override
+    public String toString() {
+        return "<fn " + declaration.name.lexeme + ">";
+    }
+}
diff --git a/src/com/craftinginterpreters/lox/Parser.java b/src/com/craftinginterpreters/lox/Parser.java
index df3ce3f..c427bc4 100644
--- a/src/com/craftinginterpreters/lox/Parser.java
+++ b/src/com/craftinginterpreters/lox/Parser.java
@@ -33,6 +33,8 @@ class Parser {
 
     private Stmt declaration() {
         try {
+            if (match(FUN))
+                return function("function");
             if (match(VAR))
                 return varDeclaration();
 
@@ -145,6 +147,26 @@ class Parser {
         return new Stmt.Expression(expr);
     }
 
+    private Stmt.Function function(String kind) {
+        Token name = consume(IDENTIFIER, "Expect " + kind + " name.");
+        consume(LEFT_PAREN, "Expect '(' after " + kind + " name.");
+        List<Token> parameters = new ArrayList();
+        if (!check(RIGHT_PAREN)) {
+            do {
+                if (parameters.size() >= 255) {
+                    error(peek(), "Can't have more than 255 parameters.");
+                }
+
+                parameters.add(consume(IDENTIFIER, "Expect parameter name."));
+            } while (match(COMMA));
+        }
+        consume(RIGHT_PAREN, "Expect ')' after parameters.");
+
+        consume(LEFT_BRACE, "Expect '{' before " + kind + " body.");
+        List<Stmt> body = block();
+        return new Stmt.Function(name, parameters, body);
+    }
+
     private List<Stmt> block() {
         List<Stmt> statements = new ArrayList<>();
 
diff --git a/src/com/craftinginterpreters/tool/GenerateAst.java b/src/com/craftinginterpreters/tool/GenerateAst.java
index 8c063bf..92c7967 100644
--- a/src/com/craftinginterpreters/tool/GenerateAst.java
+++ b/src/com/craftinginterpreters/tool/GenerateAst.java
@@ -21,6 +21,7 @@ public class GenerateAst {
                         "Unary : Token operator, Expr right", "Variable : Token name"));
         defineAst(outputDir, "Stmt",
                 Arrays.asList("Block : List<Stmt> statements", "Expression : Expr expression",
+                        "Function : Token name, List<Token> params, List<Stmt> body",
                         "If : Expr condition, Stmt thenBranch, Stmt elseBranch", "Print : Expr expression",
                         "Var : Token name, Expr initializer", "While : Expr condition, Stmt body"));
     }
-- 
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