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

Reviewed-on: #5

lexer/error.go

@@ -0,0 +1,45 @@
+package lexer
+
+import (
+	"fmt"
+	"strings"
+)
+
+var (
+	_ error = (*Error)(nil)
+)
+
+// Error represents a generic parsing error
+type Error struct {
+	Filename string
+	Line     int
+	Column   int
+
+	Content string
+	Err     error
+}
+
+func (err Error) Error() string {
+	var s []string
+
+	switch {
+	case err.Line > 0 || err.Column > 0:
+		s = append(s, fmt.Sprintf("%s:%v:%v", err.Filename, err.Line, err.Column))
+	case err.Filename != "":
+		s = append(s, err.Filename)
+	}
+
+	if err.Err != nil {
+		s = append(s, err.Err.Error())
+	}
+
+	if err.Content != "" {
+		s = append(s, fmt.Sprintf("%q", err.Content))
+	}
+
+	return strings.Join(s, ": ")
+}
+
+func (err Error) Unwrap() error {
+	return err.Err
+}

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

@@ -0,0 +1,66 @@
+package lexer
+
+import "fmt"
+
+// Position indicates a line and column pair on a file.
+// Counting starts at 1.
+type Position struct {
+	Line   int
+	Column int
+}
+
+// String generates a pretty "(Line, Column)"" representation of the Position
+func (p Position) String() string {
+	if p.Line == 0 {
+		p.Reset()
+	}
+
+	return fmt.Sprintf("(%v, %v)", p.Line, p.Column)
+}
+
+// GoString generates a string representation of the Position for %#v usage
+func (p Position) GoString() string {
+	if p.Line == 0 {
+		p.Reset()
+	}
+
+	return fmt.Sprintf("lexer.Position{%v, %v}", p.Line, p.Column)
+}
+
+// Reset places a position at (1,1)
+func (p *Position) Reset() {
+	p.Line, p.Column = 1, 1
+}
+
+// Step moves the column one place
+func (p *Position) Step() {
+	if p.Line == 0 {
+		p.Reset()
+	}
+
+	p.Column++
+}
+
+// StepN moves the column N places forward
+func (p *Position) StepN(n int) {
+	if p.Line == 0 {
+		p.Reset()
+	}
+
+	switch {
+	case n > 0:
+		p.Column += n
+	default:
+		panic(fmt.Errorf("invalid %v increment", n))
+	}
+}
+
+// StepLine moves position to the start of the next line
+func (p *Position) StepLine() {
+	if p.Line == 0 {
+		p.Reset()
+	}
+
+	p.Line++
+	p.Column = 1
+}