functions

.vscode/settings.json

@@ -1,5 +1,6 @@
 {
     "cSpell.words": [
+        "arity",
         "glox",
         "PAREN",
         "stmts"

ast_string.go

@@ -71,6 +71,17 @@ func (as *AstStringer) visitLogical(l *Logical) any {
 	return nil
 }
 
+func (as *AstStringer) visitCall(c *Call) any {
+	as.str.WriteString("(call ")
+	c.callee.accept(as)
+	for _, arg := range c.arguments {
+		arg.accept(as)
+	}
+	as.str.WriteString(")")
+
+	return nil
+}
+
 func (as *AstStringer) visitPrintStmt(p *PrintStmt) {
 	as.str.WriteString("(print ")
 	p.val.accept(as)

callable.go

@@ -0,0 +1,6 @@
+package main
+
+type Callable struct {
+	arity int
+	call  func(*Interpreter, ...any) any
+}

expr.go

@@ -1,6 +1,7 @@
 package main
 
 type ExprVisitor interface {
+	visitCall(c *Call) any
 	visitUnary(u *Unary) any
 	visitBinary(b *Binary) any
 	visitLiteral(l *Literal) any
@@ -49,6 +50,13 @@ type Logical struct {
 	right    Expr
 }
 
+type Call struct {
+	callee    Expr
+	paren     Token
+	arguments []Expr
+}
+
+func (c *Call) expr()     {}
 func (u *Unary) expr()    {}
 func (a *Assign) expr()   {}
 func (b *Binary) expr()   {}
@@ -84,3 +92,7 @@ func (a *Assign) accept(v ExprVisitor) any {
 func (l *Logical) accept(v ExprVisitor) any {
 	return v.visitLogical(l)
 }
+
+func (c *Call) accept(v ExprVisitor) any {
+	return v.visitCall(c)
+}

expr_rpn.go

@@ -61,3 +61,12 @@ func (as *ExprToRPN) visitLogical(lo *Logical) any {
 	as.str.WriteString(" or")
 	return nil
 }
+
+func (as *ExprToRPN) visitCall(c *Call) any {
+	for _, arg := range c.arguments {
+		arg.accept(as)
+	}
+	c.callee.accept(as)
+	as.str.WriteString(" call")
+	return nil
+}

globals.go

@@ -0,0 +1,13 @@
+package main
+
+import "time"
+
+func defineGlobals(env *Environment) {
+
+	env.set("clock", &Callable{
+		arity: 0,
+		call: func(i *Interpreter, arg ...any) any {
+			return time.Now().Unix()
+		},
+	})
+}

interpreter.go

@@ -9,6 +9,7 @@ import (
 
 type Interpreter struct {
 	env     *Environment
+	globals *Environment
 	errors  []error
 	brk     bool
 }
@@ -23,7 +24,17 @@ func (re *RuntimeError) Error() string {
 }
 
 func newInterpreter() *Interpreter {
-	return &Interpreter{env: newEnvironment(nil), errors: []error{}, brk: false}
+
+	globals := newEnvironment(nil)
+
+	defineGlobals(globals)
+
+	return &Interpreter{
+		env:     globals,
+		globals: globals,
+		errors:  []error{},
+		brk:     false,
+	}
 }
 
 func (i *Interpreter) interpret(stmts []Stmt) []error {
@@ -156,6 +167,36 @@ func (i *Interpreter) visitLogical(lo *Logical) any {
 	return i.evaluate(lo.right)
 }
 
+func (i *Interpreter) visitCall(c *Call) any {
+
+	callee := i.evaluate(c.callee)
+
+	args := []any{}
+
+	for _, arg := range c.arguments {
+		args = append(args, i.evaluate(arg))
+	}
+
+	callable, ok := callee.(*Callable)
+
+	if !ok {
+		i.panic(&RuntimeError{c.paren, "Can only call function and classes."})
+	}
+
+	if callable.arity != len(args) {
+		i.panic(&RuntimeError{
+			c.paren,
+			fmt.Sprintf(
+				"Expected %d arguments  but got %d",
+				callable.arity,
+				len(args),
+			),
+		})
+	}
+
+	return callable.call(i, args...)
+}
+
 func (i *Interpreter) visitPrintStmt(p *PrintStmt) {
 	fmt.Printf("%v\n", i.evaluate(p.val))
 }

parser.go

@@ -346,7 +346,41 @@ func (p *Parser) unary() Expr {
 		return &Unary{op, right}
 	}
 
-	return p.primary()
+	return p.call()
+}
+
+// call ->  primary ( "(" arguments? ")"  )*
+func (p *Parser) call() Expr {
+	expr := p.primary()
+
+	for {
+		if p.match(LEFT_PAREN) {
+			expr = p.arguments(expr)
+		} else {
+			break
+		}
+	}
+
+	return expr
+}
+
+// arguments ->  expression ( "," expression )*
+func (p *Parser) arguments(callee Expr) Expr {
+	arguments := []Expr{}
+
+	if !p.check(RIGHT_PAREN) {
+		for {
+			arguments = append(arguments, p.expression())
+
+			if !p.match(COMMA) {
+				break
+			}
+		}
+	}
+
+	paren := p.consume(RIGHT_PAREN, "Expect ')' after arguments.")
+
+	return &Call{callee, paren, arguments}
 }
 
 // primary -> NUMBER | STRING | "true" | "false" | "nil" | "(" expression ")" | IDENTIFIER

tests/functions.lox

@@ -0,0 +1,4 @@
+
+print "functions test";
+
+print clock();