[jlox] Add function calls

jlox/lox/src/main/java/xyz/ctsk/lox/AstPrinter.java

@@ -1,5 +1,7 @@
 package xyz.ctsk.lox;
 
+import java.util.stream.Collectors;
+
 public class AstPrinter {
     public static String polish(Expr expr, boolean parentheses) {
         return expr.accept(new Polish(parentheses, false));
@@ -31,6 +33,16 @@ public class AstPrinter {
             return reverse ? wrap(left, right, op) : wrap(op, left, right);
         }
 
+        @Override
+        public String visitCallExpr(Expr.Call expr) {
+            var fun = expr.callee().accept(this);
+            var args = expr.arguments().stream()
+                    .map(c -> c.accept(this))
+                    .collect(Collectors.joining(" "));
+
+            return reverse ? wrap(fun, args, "call") : wrap("call", fun, args);
+        }
+
         @Override
         public String visitGroupingExpr(Expr.Grouping expr) {
             var inner = expr.expression().accept(this);
@@ -90,6 +102,15 @@ public class AstPrinter {
                     expr.right().accept(this));
         }
 
+        @Override
+        public String visitCallExpr(Expr.Call expr) {
+            var fun = expr.callee().accept(this);
+            var args = expr.arguments().stream()
+                    .map(c -> c.accept(this))
+                    .collect(Collectors.joining(", "));
+            return fun + "(" + args + ")";
+        }
+
         @Override
         public String visitGroupingExpr(Expr.Grouping expr) {
             return '(' + expr.expression().accept(this) + ')';

jlox/lox/src/main/java/xyz/ctsk/lox/Interpreter.java

@@ -129,6 +129,25 @@ public class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
         };
     }
 
+    @Override
+    public Object visitCallExpr(Expr.Call expr) {
+        var callee = evaluate(expr.callee());
+        var arguments = expr.arguments().stream()
+                .map(this::evaluate)
+                .toList();
+
+        if (callee instanceof LoxCallable function) {
+            if (arguments.size() != function.arity()) {
+                var msg = "Expected %d arguments but got %d.".formatted(function.arity(), arguments.size());
+                throw new RuntimeError(expr.paren(), msg);
+            }
+        } else {
+            throw new RuntimeError(expr.paren(), "Can only call functions and classes.");
+        }
+
+        return null;
+    }
+
     @Override
     public Object visitGroupingExpr(Expr.Grouping expr) {
         return evaluate(expr.expression());

jlox/lox/src/main/java/xyz/ctsk/lox/LoxCallable.java

@@ -0,0 +1,8 @@
+package xyz.ctsk.lox;
+
+import java.util.List;
+
+public interface LoxCallable {
+    int arity();
+    Object call(Interpreter interpreter, List<Object> arguments);
+}

jlox/lox/src/main/java/xyz/ctsk/lox/Parser.java

@@ -39,7 +39,9 @@ import static xyz.ctsk.lox.TokenType.*;
  * term           → factor ( ( "-" | "+" ) factor )* ;
  * factor         → unary ( ( "/" | "*" ) unary )* ;
  * unary          → ( "!" | "-" ) unary
- *                | primary ;
+ *                | call ;
+ * call           → primary ( "(" arguments? ")" )* ;
+ * arguments      → expression ( "," expression )* ;
  * primary        → NUMBER | STRING | "true" | "false" | "nil"
  *                | "(" expression ")"
  *                | IDENTIFIER;
@@ -276,7 +278,39 @@ public class Parser {
             return new Expr.Unary(operator, right);
         }
 
-        return primary();
+        return call();
+    }
+
+    private Expr call() {
+        var expr = primary();
+
+        while(true) {
+            if (match(LEFT_PAREN)) {
+                expr = finishCall(expr);
+            } else {
+                break;
+            }
+        }
+
+        return expr;
+    }
+
+    private Expr finishCall(Expr callee) {
+        List<Expr> arguments = new ArrayList<>();
+
+        if (!check(RIGHT_PAREN)) {
+            do {
+                if (arguments.size() >= 255) {
+                    // DO NOT PANIC
+                    //noinspection ThrowableNotThrown
+                    error(peek(), "Can't have more than 255 arguments.");
+                }
+                arguments.add(expression());
+            } while (match(COMMA));
+        }
+
+        Token paren = consume(RIGHT_PAREN, "Expect ')' after arguments");
+        return new Expr.Call(callee, paren, arguments);
     }
 
     private Expr primary() {

jlox/lox/src/main/java/xyz/ctsk/lox/package-info.java

@@ -3,6 +3,7 @@
                 rules = {
                         @Rule(head = "Assign", body = {"Token name", "Expr value"}),
                         @Rule(head = "Binary", body = {"Expr left", "Token operator", "Expr right"}),
+                        @Rule(head = "Call", body = {"Expr callee", "Token paren", "List<Expr> arguments"}),
                         @Rule(head = "Grouping", body = {"Expr expression"}),
                         @Rule(head = "Literal", body = {"Object value"}),
                         @Rule(head = "Logical", body = {"Expr left", "Token operator", "Expr right"}),