lex colons and accept after line labels (#73)

lex.go

@@ -156,6 +156,8 @@ func lexInput(l *lexer) lexStateFn {
 		fallthrough
 	case '>':
 		return l.emitConsume(token{tokAddressMode, string(l.nextRune)}, lexInput)
+	case ':':
+		return l.emitConsume(token{tokColon, ":"}, lexInput)
 	case '\x1a':
 		return l.consume(lexInput)
 	default:

parser.go

@@ -220,6 +220,8 @@ func parseComment(p *parser) parseStateFn {
 // parseLabels consumes text tokens until an op is read
 // label text token: parseLabels
 // op text token: parseOp
+// colon: parseColon
+// newline / comments: consume
 // anyting else: nil
 func parseLabels(p *parser) parseStateFn {
 	if p.nextToken.IsOp() {
@@ -229,6 +231,10 @@ func parseLabels(p *parser) parseStateFn {
 		return parseOp
 	}
 
+	if p.nextToken.typ == tokColon {
+		return parseColon
+	}
+
 	_, ok := p.symbols[p.nextToken.val]
 	if ok {
 		p.err = fmt.Errorf("line %d: symbol '%s' redefined", p.line, p.nextToken.val)
@@ -251,6 +257,30 @@ func parseLabels(p *parser) parseStateFn {
 	return parseLabels
 }
 
+// from: parseLabels
+// newline or comments: parseColon
+// op: parseOp
+// anything else: nil
+func parseColon(p *parser) parseStateFn {
+	p.next()
+
+	// just consume newlines and comments for now
+	if p.nextToken.typ == tokNewline || p.nextToken.typ == tokComment {
+		p.next()
+		return parseColon
+	}
+
+	if p.nextToken.IsOp() {
+		if p.nextToken.IsPseudoOp() {
+			return parsePseudoOp
+		}
+		return parseOp
+	}
+
+	p.err = fmt.Errorf("line %d: op expected after colon, got '%s'", p.line, p.nextToken)
+	return nil
+}
+
 // from: parseLabels
 // comment: parseComment
 // newline: parseLine

parser_test.go

@@ -76,6 +76,21 @@ func TestParserPositive(t *testing.T) {
 				newlines: 1,
 			}},
 		},
+		{
+			input: "a: mov $0, $1 ; comment\n",
+			output: []sourceLine{{
+				line:     1,
+				labels:   []string{"a"},
+				typ:      lineInstruction,
+				op:       "mov",
+				amode:    "$",
+				a:        []token{{typ: tokNumber, val: "0"}},
+				bmode:    "$",
+				b:        []token{{typ: tokNumber, val: "1"}},
+				comment:  "; comment",
+				newlines: 1,
+			}},
+		},
 		{
 			input: "mov $ -1, $ 2 + 2\n",
 			output: []sourceLine{{

token.go

@@ -11,6 +11,7 @@ const (
 	tokNumber                       // (optionally) signed integer
 	tokExprOp                       // + - * / % ==
 	tokComma
+	tokColon
 	tokParenL
 	tokParenR
 	tokComment // includes semi-colon, no newline char