parser location doesn't need to be in the context, does it?

builtins.go

@@ -286,7 +286,7 @@ func (b *Builtins) Rot(s *Stack) func() error {
 func (b *Builtins) Words(d Dictionary) func() error {
 	return func() error {
 		for n := range d {
-			fmt.Printf("%s ", n)
+			fmt.Printf("%s %s\n", n, d[n].Source)
 		}
 		return nil
 	}
@@ -341,6 +341,41 @@ func (b *Builtins) RFetch(s *Stack, r *Stack) func() error {
 	}
 }
 
+// If checks if NOS != 0 and conditionally executes any following statements if so
+func (b *Builtins) If(s *Stack, r *Stack) func() error {
+	return func() error {
+		return nil
+	}
+}
+
+// Else executes a separate piece of code if NOS == 0 after an if check
+func (b *Builtins) Else(s *Stack, r *Stack) func() error {
+	return func() error {
+		return nil
+	}
+}
+
+// Then ends an If/Else block
+func (b *Builtins) Then(s *Stack, r *Stack) func() error {
+	return func() error {
+		return nil
+	}
+}
+
+// Do sets up a loop
+func (b *Builtins) Do(s *Stack, r *Stack) func() error {
+	return func() error {
+		return nil
+	}
+}
+
+// Loop closes a loop
+func (b *Builtins) Loop(s *Stack, r *Stack) func() error {
+	return func() error {
+		return nil
+	}
+}
+
 // CR prints a newline to standard out
 func (b *Builtins) CR() func() error {
 	return func() error {

eval.go

@@ -6,7 +6,7 @@ import (
 	"strings"
 )
 
-// Context is a set of Dictionary + Stack representing a runtime environment
+// Context is a set of Dictionary + Stacks representing a runtime environment
 type Context struct {
 	Dictionary Dictionary
 	Stack      *Stack
@@ -17,6 +17,7 @@ type Context struct {
 func (c *Context) Eval(line string) error {
 	// state
 	var word []byte
+	var words []string
 	var comment bool
 	immediate := true
 
@@ -37,26 +38,27 @@ func (c *Context) Eval(line string) error {
 			if len(word) == 0 {
 				if line[i] == ':' {
 					immediate = false
-				}
-			} else {
-				if line[i-1] == ' ' && line[i] == ';' {
-					def := strings.SplitN(strings.TrimSpace(string(word)), " ", 2)
-					c.Dictionary.AddWord(def[0], nil, def[1]+" ")
+				} else if line[i-1] == ' ' && line[i] == ';' {
+					c.Dictionary.AddWord(words[0], nil, words[1:])
 					word = []byte{}
 					immediate = true
-				} else {
-					word = append(word, line[i])
 				}
+			} else {
+				word = append(word, line[i])
 			}
 		case ' ':
 			if !immediate { // continue building our subroutine if we're not in immediate mode...
-				word = append(word, line[i])
+				if len(word) != 0 { // don't add empty words to our list
+					words = append(words, strings.TrimSpace(string(word)))
+					word = []byte{}
+				}
 				continue
 			}
 			if len(word) == 0 || comment {
 				// empty space, just continue...
 				continue
 			}
+
 			int, err := strconv.Atoi(string(word))
 			if err == nil {
 				// it was a number! put it on the stack.
@@ -64,6 +66,7 @@ func (c *Context) Eval(line string) error {
 				word = []byte{}
 				continue
 			}
+
 			// it wasn't a number. Is it a word we know?
 			w, err := c.Dictionary.GetWord(string(word))
 			if err != nil {
@@ -76,12 +79,17 @@ func (c *Context) Eval(line string) error {
 					return err
 				}
 				word = []byte{}
-			} else if w.Source != "" {
+			} else if len(w.Source) != 0 {
 				// user-defined word; let's descend...
-				err := c.Eval(w.Source)
+				c.RStack.Push(i)
+				err := c.Eval(strings.Join(w.Source, " ") + " ")
 				if err != nil {
 					return err
 				}
+				i, err = c.RStack.Pop()
+				if err != nil {
+					return fmt.Errorf("error while popping from return stack: %v", err)
+				}
 				word = []byte{}
 			}
 		default:

main.go

@@ -14,31 +14,33 @@ func main() {
 
 	dict := Dictionary{}
 	b := &Builtins{}
-	dict.AddWord("+", b.Add(&stack), "")
-	dict.AddWord("-", b.Sub(&stack), "")
-	dict.AddWord("*", b.Mul(&stack), "")
-	dict.AddWord("/", b.Div(&stack), "")
-	dict.AddWord(".", b.Print(&stack), "")
-	dict.AddWord("=", b.Eq(&stack), "")
-	dict.AddWord("0=", nil, "0 = ")
-	dict.AddWord("<>", b.NEq(&stack), "")
-	dict.AddWord(">", b.Gt(&stack), "")
-	dict.AddWord("<", b.Lt(&stack), "")
-	dict.AddWord(">=", b.GtEq(&stack), "")
-	dict.AddWord("<=", b.LtEq(&stack), "")
-	dict.AddWord("DUP", b.Dup(&stack), "")
-	dict.AddWord("SWAP", b.Swap(&stack), "")
-	dict.AddWord("OVER", b.Over(&stack), "")
-	dict.AddWord("DROP", b.Drop(&stack), "")
-	dict.AddWord("ROT", b.Rot(&stack), "")
-	dict.AddWord("WORDS", b.Words(dict), "")
-	dict.AddWord(".S", b.Debug(&stack), "")
-	dict.AddWord("EMIT", b.Emit(&stack), "")
-	dict.AddWord("R>", b.RFrom(&stack, &rstack), "")
-	dict.AddWord(">R", b.ToR(&stack, &rstack), "")
-	dict.AddWord("R@", b.RFetch(&stack, &rstack), "")
-	dict.AddWord("CR", b.CR(), "")
-	dict.AddWord("QUIT", b.Quit(), "")
+	dict.AddWord("+", b.Add(&stack), nil)
+	dict.AddWord("-", b.Sub(&stack), nil)
+	dict.AddWord("*", b.Mul(&stack), nil)
+	dict.AddWord("/", b.Div(&stack), nil)
+	dict.AddWord(".", b.Print(&stack), nil)
+	dict.AddWord("=", b.Eq(&stack), nil)
+	dict.AddWord("0=", nil, []string{"0", "="})
+	dict.AddWord("<>", b.NEq(&stack), nil)
+	dict.AddWord(">", b.Gt(&stack), nil)
+	dict.AddWord("<", b.Lt(&stack), nil)
+	dict.AddWord(">=", b.GtEq(&stack), nil)
+	dict.AddWord("<=", b.LtEq(&stack), nil)
+	dict.AddWord("0<", nil, []string{"0", "<"})
+	dict.AddWord("0>", nil, []string{"0", ">"})
+	dict.AddWord("DUP", b.Dup(&stack), nil)
+	dict.AddWord("SWAP", b.Swap(&stack), nil)
+	dict.AddWord("OVER", b.Over(&stack), nil)
+	dict.AddWord("DROP", b.Drop(&stack), nil)
+	dict.AddWord("ROT", b.Rot(&stack), nil)
+	dict.AddWord("WORDS", b.Words(dict), nil)
+	dict.AddWord(".S", b.Debug(&stack), nil)
+	dict.AddWord("EMIT", b.Emit(&stack), nil)
+	dict.AddWord("R>", b.RFrom(&stack, &rstack), nil)
+	dict.AddWord(">R", b.ToR(&stack, &rstack), nil)
+	dict.AddWord("R@", b.RFetch(&stack, &rstack), nil)
+	dict.AddWord("CR", b.CR(), nil)
+	dict.AddWord("QUIT", b.Quit(), nil)
 
 	c := Context{
 		Dictionary: dict,
@@ -64,8 +66,9 @@ func main() {
 			fmt.Printf("bye\n")
 			os.Exit(0)
 		} else if err != nil {
-			fmt.Printf("error in evaluation: %v\n", err)
+			fmt.Printf("error in evaluation: %v", err)
+		} else {
+			fmt.Print("ok")
 		}
-		fmt.Print("ok")
 	}
 }

words.go

@@ -9,11 +9,11 @@ type Dictionary map[string]Word
 type Word struct {
 	Name   string
 	Impl   func() error
-	Source string
+	Source []string
 }
 
 // AddWord inserts a new word into the dictonary, optionally overwriting the existing word
-func (d Dictionary) AddWord(name string, impl func() error, source string) {
+func (d Dictionary) AddWord(name string, impl func() error, source []string) {
 	d[name] = Word{
 		Name:   name,
 		Impl:   impl,

words_test.go

@@ -5,7 +5,7 @@ import "testing"
 func TestDictionary(t *testing.T) {
 	d := Dictionary{}
 
-	d.AddWord("INC", nil, "1 + ")
+	d.AddWord("INC", nil, []string{"1", "+"})
 	w, err := d.GetWord("INC")
 	if err != nil {
 		t.Fail()
@@ -16,7 +16,7 @@ func TestDictionary(t *testing.T) {
 	if w.Impl != nil {
 		t.Fail()
 	}
-	if w.Source != "1 +" {
+	if len(w.Source) != 2 || w.Source[0] != "1" || w.Source[1] != "+" {
 		t.Fail()
 	}
 }