Improve error messages

rpn/lexer.go

@@ -11,7 +11,7 @@ type Lexer struct {
 	input *Input
 }
 
-func (l *Lexer) parseNumber() (float64, error) {
+func (l *Lexer) parseNumber(negative bool) (*Token, error) {
 	numStr := ""
 	char := l.input.NextChar()
 	for {
@@ -25,10 +25,14 @@ func (l *Lexer) parseNumber() (float64, error) {
 
 	num, err := strconv.ParseFloat(numStr, 64)
 	if err != nil {
-		return 0, err
+		return nil, err
+	}
+	if negative {
+		numStr = "-" + numStr
+		num = -num
 	}
 
-	return num, nil
+	return &Token{number, 0, num, numStr}, nil
 }
 
 func (l *Lexer) parseWord() (*Token, error) {
@@ -45,25 +49,25 @@ func (l *Lexer) parseWord() (*Token, error) {
 
 	switch word {
 	case "sqrt":
-		return &Token{unaryOp, sqrt, 0}, nil
+		return &Token{unaryOp, sqrt, 0, word}, nil
 	case "dec":
-		return &Token{dec, 0, 0}, nil
+		return &Token{dec, 0, 0, word}, nil
 	case "bin":
-		return &Token{bin, 0, 0}, nil
+		return &Token{bin, 0, 0, word}, nil
 	case "hex":
-		return &Token{hex, 0, 0}, nil
+		return &Token{hex, 0, 0, word}, nil
 	case "pi":
-		return &Token{number, 0, math.Pi}, nil
+		return &Token{number, 0, math.Pi, word}, nil
 	case "pop":
-		return &Token{pop, 0, 0}, nil
+		return &Token{pop, 0, 0, word}, nil
 	case "swap":
-		return &Token{swap, 0, 0}, nil
+		return &Token{swap, 0, 0, word}, nil
 	case "clr":
-		return &Token{clr, 0, 0}, nil
+		return &Token{clr, 0, 0, word}, nil
 	case "help":
-		return &Token{help, 0, 0}, nil
+		return &Token{help, 0, 0, word}, nil
 	case "exit":
-		return &Token{exit, 0, 0}, nil
+		return &Token{exit, 0, 0, word}, nil
 	default:
 		return nil, fmt.Errorf("Unknown input: %s", word)
 	}
@@ -71,7 +75,6 @@ func (l *Lexer) parseWord() (*Token, error) {
 
 func (l *Lexer) Parse(input string) ([]*Token, error) {
 	var err error
-	var num float64
 	var token *Token
 	l.input = NewInput(input)
 	tokens := []*Token{}
@@ -84,30 +87,29 @@ func (l *Lexer) Parse(input string) ([]*Token, error) {
 		switch char {
 		case '+':
 			l.input.Eat()
-			token = &Token{binaryOp, plus, 0}
+			token = &Token{binaryOp, plus, 0, string(char)}
 		case '-':
 			char = l.input.Eat()
 			if unicode.IsNumber(char) {
-				num, err = l.parseNumber()
+				token, err = l.parseNumber(true)
-				token = &Token{number, 0, -num}
 				if err != nil {
 					return nil, err
 				}
 			} else {
-				token = &Token{binaryOp, minus, 0}
+				token = &Token{binaryOp, minus, 0, string(char)}
 			}
 		case '*':
 			l.input.Eat()
-			token = &Token{binaryOp, multiply, 0}
+			token = &Token{binaryOp, multiply, 0, string(char)}
 		case '/':
 			l.input.Eat()
-			token = &Token{binaryOp, divide, 0}
+			token = &Token{binaryOp, divide, 0, string(char)}
 		case '%':
 			l.input.Eat()
-			token = &Token{binaryOp, mod, 0}
+			token = &Token{binaryOp, mod, 0, string(char)}
 		case '^':
 			l.input.Eat()
-			token = &Token{binaryOp, power, 0}
+			token = &Token{binaryOp, power, 0, string(char)}
 		case ' ':
 			l.input.Eat()
 			continue
@@ -115,24 +117,23 @@ func (l *Lexer) Parse(input string) ([]*Token, error) {
 			l.input.Eat()
 			continue
 		case 0x04: // Ctrl-D
-			token = &Token{exit, 0, 0}
+			token = &Token{exit, 0, 0, "^D"}
 		case '?':
 			l.input.Eat()
-			token = &Token{help, 0, 0}
+			token = &Token{help, 0, 0, string(char)}
 		default:
 			if unicode.IsNumber(char) {
-				num, err = l.parseNumber()
+				token, err = l.parseNumber(false)
 				if err != nil {
 					return nil, err
 				}
-				token = &Token{number, 0, num}
 			} else if unicode.IsLetter(char) {
 				token, err = l.parseWord()
 				if err != nil {
 					return nil, err
 				}
 			} else {
-				return nil, fmt.Errorf("Unknown input: %c", char)
+				return nil, fmt.Errorf("Invalid input: %c", char)
 			}
 		}
 

rpn/rpn.go

@@ -1,12 +1,10 @@
 package rpn
 
 import (
-	"errors"
+	"fmt"
 	"math"
 )
 
-var ErrExit = errors.New("exit")
-
 type RPN struct {
 	stack *Stack
 	lexer *Lexer
@@ -62,10 +60,15 @@ func (r *RPN) Eval(input string) error {
 				if a == 0 {
 					r.stack.Push(b)
 					r.stack.Push(a)
-					return errors.New("can't divide by zero")
+					return fmt.Errorf("Can't divide by zero")
 				}
 				r.stack.Push(b / a)
 			case mod:
+				if a == 0 {
+					r.stack.Push(b)
+					r.stack.Push(a)
+					return fmt.Errorf("Can't divide by zero")
+				}
 				r.stack.Push(float64(int64(b) % int64(a)))
 			case power:
 				r.stack.Push(math.Pow(b, a))
@@ -94,9 +97,9 @@ func (r *RPN) Eval(input string) error {
 		case help:
 			printHelp()
 		case exit:
-			return ErrExit
+			return fmt.Errorf("exit")
 		default:
-			return errors.New("Unknown operation")
+			return fmt.Errorf("Operation not implemented: %s", token.Original)
 		}
 	}
 

rpn/stack.go

@@ -1,15 +1,11 @@
 package rpn
 
 import (
-	"errors"
 	"fmt"
 	"math"
 )
 
-var (
+var ErrNotEnoughValuesTmpl = "Need at least %d values on the stack to perform this operation"
-	ErrStackEmpty      = errors.New("stack is empty")
-	ErrNotEnoughValues = errors.New("not enough values on stack")
-)
 
 type Stack struct {
 	values []float64
@@ -22,7 +18,7 @@ func (s *Stack) Push(value float64) {
 func (s *Stack) Pop() (float64, error) {
 	count := s.Len()
 	if count == 0 {
-		return 0, ErrStackEmpty
+		return 0, fmt.Errorf(ErrNotEnoughValuesTmpl, 1)
 	}
 	value := s.values[count-1]
 	s.values = s.values[:count-1]
@@ -32,7 +28,7 @@ func (s *Stack) Pop() (float64, error) {
 func (s *Stack) Pop2() (float64, float64, error) {
 	count := s.Len()
 	if count < 2 {
-		return 0, 0, ErrNotEnoughValues
+		return 0, 0, fmt.Errorf(ErrNotEnoughValuesTmpl, 2)
 	}
 	a := s.values[count-1]
 	b := s.values[count-2]
@@ -47,7 +43,7 @@ func (s *Stack) Len() int {
 func (s *Stack) Swap() error {
 	count := s.Len()
 	if count < 2 {
-		return ErrNotEnoughValues
+		return fmt.Errorf(ErrNotEnoughValuesTmpl, 2)
 	}
 	a := s.values[count-1]
 	b := s.values[count-2]

rpn/token.go

@@ -32,4 +32,5 @@ type Token struct {
 	Type     TokenType
 	Operator Operator
 	Value    float64
+	Original string
 }