Add logging to lex command

lex command writes logs out to the maleeni-lex.log file.
When you generate a lexer using driver.NewLexer(), you can choose whether the lexer writes logs or not.

1 files changed, 42 insertions, 0 deletions

diff --git a/log/logger.go b/log/logger.go
new file mode 100644
index 0000000..770f1c1
--- /dev/null
+++ b/log/logger.go
@@ -0,0 +1,42 @@
+package log
+
+import (
+	"fmt"
+	"io"
+)
+
+type Logger interface {
+	Log(format string, a ...interface{})
+}
+
+var (
+	_ Logger = &logger{}
+	_ Logger = &nopLogger{}
+)
+
+type logger struct {
+	w io.Writer
+}
+
+func NewLogger(w io.Writer) (*logger, error) {
+	if w == nil {
+		return nil, fmt.Errorf("w is nil; NewLogger() needs a writer")
+	}
+	return &logger{
+		w: w,
+	}, nil
+}
+
+func (l *logger) Log(format string, a ...interface{}) {
+	fmt.Fprintf(l.w, format+"\n", a...)
+}
+
+type nopLogger struct {
+}
+
+func NewNopLogger() *nopLogger {
+	return &nopLogger{}
+}
+
+func (l *nopLogger) Log(format string, a ...interface{}) {
+}