Error handling is now done with a custom error in the file package

file/error.go

@@ -0,0 +1,72 @@
+package file
+
+import "fmt"
+
+type ErrorKind int
+
+const (
+	ErrorKindError ErrorKind = iota
+	ErrorKindWarn
+)
+
+type Error struct {
+	Location
+	width   int
+	message string
+	kind    ErrorKind
+}
+
+// NewError creates a new error at the specified location.
+func NewError (
+	location Location,
+	width int,
+	message string,
+	kind ErrorKind,
+) (
+	err *Error,
+) {
+	return &Error {
+		Location: location,
+		width:    width,
+		message:  message,
+		kind:     kind,
+	}
+}
+
+// Error returns a formatted error message as a string.
+func (err Error) Error () (formattedMessage string) {
+	switch err.kind {
+	case ErrorKindError:
+		formattedMessage += "ERR"
+	case ErrorKindWarn:
+		formattedMessage += "!!!"
+	}
+
+	// print information about the location of the mistake
+	if err.width > 0 {
+		formattedMessage += fmt.Sprint (
+			" ", err.Location.row + 1,
+			":", err.Location.column + 1)
+	}
+	formattedMessage += " in " +  err.Location.file.path + "\n"
+	
+	if err.width > 0 {
+		// print erroneous line
+		formattedMessage +=
+			err.Location.file.lines[err.Location.row] + "\n"
+
+		// print an arrow with a tail spanning the width of the mistake
+		columnCountdown := err.Location.column
+		for columnCountdown > 0 {
+			formattedMessage += " "
+			columnCountdown --
+		}
+		for err.width > 1 {
+			formattedMessage += "-"
+		}
+		formattedMessage += "-\n"
+	}
+	formattedMessage += err.message + "-\n"
+
+	return
+}

file/file.go

@@ -1,11 +1,8 @@
 package file
 
 import "os"
-import "log"
 import "bufio"
 
-var logger = log.New(os.Stderr, "", 0)
-
 // File represents a read only file that can print out formatted errors.
 type File struct {
 	path          string
@@ -104,47 +101,6 @@ 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, "!!!")
-}
-
 // Location returns a location struct describing the current position inside of
 // the file. This can be stored and used to print errors.
 func (file *File) Location () (location Location) {

file/location.go

@@ -7,13 +7,3 @@ type Location struct {
 	row    int
 	column int
 }
-
-// Error prints an error at this location.
-func (location Location) Error (width int, message string) {
-	location.file.Error(location.column, location.row, width, message)
-}
-
-// Warn prints a warning at this location.
-func (location Location) Warn (width int, message string) {
-	location.file.Warn(location.column, location.row, width, message)
-}