Merge pull request 'lexer: Reader.Accept(), AcceptAll(), and StateFn' (#5)

Reviewed-on: #5

lexer/lexer.go

@@ -1,17 +1,31 @@
 // Package lexer provides basic helpers to implement parsers
 package lexer
 
+import (
+	"errors"
+	"io"
+)
+
 // StateFn is a State Function of the parser
 type StateFn func() (StateFn, error)
 
 // Run runs a state machine until the state function either
 // returns nil or an error
 func Run(fn StateFn) error {
-	var err error
+	for fn != nil {
+		var err error
 
-	for fn != nil && err == nil {
 		fn, err = fn()
+		switch {
+		case errors.Is(err, io.EOF):
+			// EOF
+			return nil
+		case err != nil:
+			// failed
+			return err
+		}
 	}
 
-	return err
+	// ended
+	return nil
 }

lexer/position.go

@@ -41,28 +41,26 @@ func (p *Position) Step() {
 	p.Column++
 }
 
-// Next returns a new Position one rune forward
-// on the line
-func (p Position) Next() Position {
+// StepN moves the column N places forward
+func (p *Position) StepN(n int) {
 	if p.Line == 0 {
 		p.Reset()
 	}
 
-	return Position{
-		Line:   p.Line,
-		Column: p.Column + 1,
+	switch {
+	case n > 0:
+		p.Column += n
+	default:
+		panic(fmt.Errorf("invalid %v increment", n))
 	}
 }
 
-// NextLine returns a new Position at the begining of the next
-// line.
-func (p Position) NextLine() Position {
+// StepLine moves position to the start of the next line
+func (p *Position) StepLine() {
 	if p.Line == 0 {
 		p.Reset()
 	}
 
-	return Position{
-		Line:   p.Line + 1,
-		Column: 1,
-	}
+	p.Line++
+	p.Column = 1
 }