File is now capable of printing errors

file/file.go

@@ -1,22 +1,22 @@
 package file
 
 import "os"
-import "path/filepath"
+import "log"
 
+var logger = log.New(os.Stderr, "", 0)
+
+// File represents a read only file that can print out formatted errors.
 type File struct {
 	path        string
-	moduleName  string
 	file        *os.File
 	currentLine int
 	lines       [][]byte
 }
 
-// Open opens the file specified by path and returns a new File struct. The
-// module name is automatically inferred through hte file's parent directory.
+// Open opens the file specified by path and returns a new File struct.
 func Open (path string) (file *File, err error) {
 	file = &File {
 		path:  path,
-		moduleName: filepath.Dir(path),
 		lines: [][]byte { []byte { } },
 	}
 
@@ -39,6 +39,7 @@ func (file *File) Stat () (fileInfo os.FileInfo, err error) {
 func (file *File) Read (bytes []byte) (amountRead int, err error) {
 	amountRead, err = file.file.Read(bytes)
 
+	// store the character in the file
 	for _, char := range bytes {
 		if char == '\n' {
 			file.lines = append(file.lines, []byte { })
@@ -58,3 +59,44 @@ func (file *File) Read (bytes []byte) (amountRead int, err error) {
 func (file *File) Close () {
 	file.file.Close()
 }
+
+// mistake prints an informational message about a mistake that the user made.
+func (file *File) mistake (column, row, width int, message, symbol string) {
+	logger.Print(symbol)
+
+	// print information about the location of the mistake
+	if width > 0 {
+		logger.Print(" ", row + 1, ":", column + 1)
+	}
+	logger.Println(" in", file.path)
+	
+	if width > 0 {
+		// print erroneous line
+		logger.Println(file.lines[row])
+
+		// print an arrow with a tail spanning the width of the mistake
+		for column > 0 {
+			logger.Print(" ")
+			column --
+		}
+		for width > 1 {
+			logger.Print("-")
+		}
+		logger.Println("^")
+	}
+	logger.Println(message)
+}
+
+// Error prints an error at row and column spanning width amount of runes, and
+// a message describing the error. If width is zero, neither the line nor the
+// location information is printed.
+func (file *File) Error (column, row, width int, message string) {
+	file.mistake(column, row, width, message, "ERR")
+}
+
+// Warn prints a warning at row and column spanning width amount of runes, and
+// a message describing the error. If width is zero, neither the line nor the
+// location information is printed.
+func (file *File) Warn (column, row, width int, message string) {
+	file.mistake(column, row, width, message, "!!!")
+}