add start to parser

parser/parser.go

@@ -0,0 +1,58 @@
+package parser
+
+import (
+	"io"
+
+	"github.com/brettlangdon/gython/ast"
+	"github.com/brettlangdon/gython/errorcode"
+	"github.com/brettlangdon/gython/scanner"
+	"github.com/brettlangdon/gython/token"
+)
+
+type Parser struct {
+	tokenizer *scanner.Scanner
+
+	tokenBuffer []*token.Token
+}
+
+func (parser *Parser) nextToken() *token.Token {
+	if len(parser.tokenBuffer) > 0 {
+		last := len(parser.tokenBuffer) - 1
+		next := parser.tokenBuffer[last]
+		parser.tokenBuffer = parser.tokenBuffer[:last]
+		return next
+	}
+
+	return parser.tokenizer.NextToken()
+}
+
+func (parser *Parser) unreadToken(tok *token.Token) {
+	parser.tokenBuffer = append(parser.tokenBuffer, tok)
+}
+
+func (parser *Parser) parseFileInput() *ast.FileInput {
+	root := ast.NewFileInput()
+	for parser.tokenizer.State() == errorcode.E_OK {
+		next := parser.nextToken()
+		if next.ID == token.NEWLINE {
+			root.AppendToken(next)
+		} else if next.ID == token.ENDMARKER {
+			break
+		} else {
+			parser.unreadToken(next)
+			// TODO: parser.parseStatement()
+			break
+		}
+	}
+
+	return root
+}
+
+func ParseReader(r io.Reader) *ast.FileInput {
+	parser := &Parser{
+		tokenizer:   scanner.NewScanner(r),
+		tokenBuffer: make([]*token.Token, 0),
+	}
+
+	return parser.parseFileInput()
+}