1 files changed, 107 insertions, 0 deletions
diff --git a/parser/errors.go b/parser/errors.go
new file mode 100644
index 0000000..c2ed049
--- /dev/null
+++ b/parser/errors.go
@@ -0,0 +1,107 @@
+package parser
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+type ErrorLister interface {
+	Errors() []error
+}
+
+func (e errList) Errors() []error {
+	return e
+}
+
+// ParserError is the public interface to errors of type parserError
+type ParserError interface {
+	Error() string
+	InnerError() error
+	Pos() (int, int, int)
+	Expected() []string
+}
+
+func (p *parserError) InnerError() error {
+	return p.Inner
+}
+
+func (p *parserError) Pos() (line, col, offset int) {
+	return p.pos.line, p.pos.col, p.pos.offset
+}
+
+func (p *parserError) Expected() []string {
+	return p.expected
+}
+
+func CaretErrors(err error, input string) error {
+	if el, ok := err.(ErrorLister); ok {
+		var buffer bytes.Buffer
+		for _, e := range el.Errors() {
+			err1, shouldReturn := caretError(e, input, buffer, err)
+			if shouldReturn {
+				return err1
+			}
+		}
+		return errors.New(buffer.String())
+	}
+	return err
+}
+
+func caretError(e error, input string, buffer bytes.Buffer, err error) (error, bool) {
+	if parserErr, ok := e.(ParserError); ok {
+		_, col, off := parserErr.Pos()
+		line := extractLine(input, off)
+		if col >= len(line) {
+			col = len(line) - 1
+		} else {
+			if col > 0 {
+				col--
+			}
+		}
+		if col < 0 {
+			col = 0
+		}
+		pos := col
+		for _, chr := range line[:col] {
+			if chr == '\t' {
+				pos += 7
+			}
+		}
+		fmt.Fprintf(&buffer, "%s\n%s\n%s\n", line, strings.Repeat(" ", pos)+"^", err.Error())
+
+		return err, true
+	} else {
+		return err, true
+	}
+	return nil, false
+}
+
+func extractLine(input string, initPos int) string {
+	if initPos < 0 {
+		initPos = 0
+	}
+	if initPos >= len(input) && len(input) > 0 {
+		initPos = len(input) - 1
+	}
+	startPos := initPos
+	endPos := initPos
+	for ; startPos > 0; startPos-- {
+		if input[startPos] == '\n' {
+			if startPos != initPos {
+				startPos++
+				break
+			}
+		}
+	}
+	for ; endPos < len(input); endPos++ {
+		if input[endPos] == '\n' {
+			if endPos == initPos {
+				endPos++
+			}
+			break
+		}
+	}
+	return input[startPos:endPos]
+}