finished chapter 1

lexer/lexer.go

@@ -27,36 +27,107 @@ func (l *Lexer) readChar() {
 	l.readPosition += 1
 }
 
+func (l *Lexer) readIdentifier() string {
+	position := l.position
+	for isLetter(l.ch) {
+		l.readChar()
+	}
+	return l.input[position:l.position]
+}
+
+func (l *Lexer) readNumber() string {
+	position := l.position
+	for isDigit(l.ch) {
+		l.readChar()
+	}
+	return l.input[position:l.position]
+}
+
+func isLetter(ch byte) bool {
+	return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_'
+}
+
+func isDigit(ch byte) bool {
+	return '0' <= ch && ch <= '9'
+}
+
+func (l *Lexer) skipWhitespace() {
+	for l.ch == ' ' || l.ch == '\t' || l.ch == '\n' || l.ch == '\r' {
+		l.readChar()
+	}
+}
+
+func newToken(tokenType token.TokenType, ch byte) token.Token {
+	return token.Token{Type: tokenType, Literal: string(ch)}
+}
+func (l *Lexer) peekChar() byte {
+	if l.readPosition >= len(l.input) {
+		return 0
+	} else {
+		return l.input[l.readPosition]
+	}
+}
+
 func (l *Lexer) NextToken() token.Token {
 	var tok token.Token
 
 	l.skipWhitespace()
 
 	switch l.ch {
 	case '=':
-		tok = newToken(token.ASSIGN, l.ch)
+		if l.peekChar() == '=' {
+			ch := l.ch
+			l.readChar()
+			literal := string(ch) + string(l.ch)
+			tok = token.Token{Type: token.EQ, Literal: literal}
+		} else {
+			tok = newToken(token.ASSIGN, l.ch)
+		}
+	case '+':
+		tok = newToken(token.PLUS, l.ch)
+	case '-':
+		tok = newToken(token.MINUS, l.ch)
+	case '!':
+		if l.peekChar() == '=' {
+			ch := l.ch
+			l.readChar()
+			literal := string(ch) + string(l.ch)
+			tok = token.Token{Type: token.NOT_EQ, Literal: literal}
+		} else {
+			tok = newToken(token.BANG, l.ch)
+		}
+	case '/':
+		tok = newToken(token.SLASH, l.ch)
+	case '*':
+		tok = newToken(token.ASTERISK, l.ch)
+	case '<':
+		tok = newToken(token.LT, l.ch)
+	case '>':
+		tok = newToken(token.GT, l.ch)
 	case ';':
 		tok = newToken(token.SEMICOLON, l.ch)
-	case '(':
-		tok = newToken(token.LPAREN, l.ch)
-	case ')':
-		tok = newToken(token.RPAREN, l.ch)
 	case ',':
 		tok = newToken(token.COMMA, l.ch)
-	case '+':
-		tok = newToken(token.PLUS, l.ch)
 	case '{':
 		tok = newToken(token.LBRACE, l.ch)
 	case '}':
 		tok = newToken(token.RBRACE, l.ch)
-	case '0':
+	case '(':
+		tok = newToken(token.LPAREN, l.ch)
+	case ')':
+		tok = newToken(token.RPAREN, l.ch)
+	case 0:
 		tok.Literal = ""
 		tok.Type = token.EOF
 	default:
 		if isLetter(l.ch) {
 			tok.Literal = l.readIdentifier()
 			tok.Type = token.LookupIdent(tok.Literal)
 			return tok
+		} else if isDigit(l.ch) {
+			tok.Type = token.INT
+			tok.Literal = l.readNumber()
+			return tok
 		} else {
 			tok = newToken(token.ILLEGAL, l.ch)
 		}
@@ -65,25 +136,3 @@ func (l *Lexer) NextToken() token.Token {
 	l.readChar()
 	return tok
 }
-
-func (l *Lexer) readIdentifier() string {
-	position := l.position
-	for isLetter(l.ch) {
-		l.readChar()
-	}
-	return l.input[position:l.position]
-}
-
-func isLetter(ch byte) bool {
-	return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_'
-}
-
-func (l *Lexer) skipWhitespace() {
-	for l.ch == ' ' || l.ch == '\t' || l.ch == '\n' || l.ch == '\r' {
-		l.readChar()
-	}
-}
-
-func newToken(tokenType token.TokenType, ch byte) token.Token {
-	return token.Token{Type: tokenType, Literal: string(ch)}
-}

main.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/user"
+
+	"github.com/zizouhuweidi/go-terpreter/repl"
+)
+
+func main() {
+	user, err := user.Current()
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Printf("Hello %s! This is the Monkey programming language!\n",
+		user.Username)
+	fmt.Printf("Feel free to type in commands\n")
+	repl.Start(os.Stdin, os.Stdout)
+}

repl/repl.go

@@ -0,0 +1,33 @@
+package repl
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+
+	"github.com/zizouhuweidi/go-terpreter/lexer"
+	"github.com/zizouhuweidi/go-terpreter/token"
+)
+
+const PROMPT = ">> "
+
+func Start(in io.Reader, out io.Writer) {
+	scanner := bufio.NewScanner(in)
+
+	for {
+		fmt.Printf(PROMPT)
+		scanned := scanner.Scan()
+		if !scanned {
+			return
+		}
+
+		line := scanner.Text()
+
+		l := lexer.New(line)
+
+		for tok := l.NextToken(); tok.Type != token.EOF; tok = l.NextToken() {
+			fmt.Printf("%+v\n", tok)
+		}
+	}
+
+}

token/token.go

@@ -16,8 +16,18 @@ const (
 	INT   = "INT"   // 1343456
 
 	// Operators
-	ASSIGN = "="
-	PLUS   = "+"
+	ASSIGN   = "="
+	PLUS     = "+"
+	MINUS    = "-"
+	BANG     = "!"
+	ASTERISK = "*"
+	SLASH    = "/"
+
+	LT = "<"
+	GT = ">"
+
+	EQ     = "=="
+	NOT_EQ = "!="
 
 	// Delimiters
 	COMMA     = ","
@@ -31,11 +41,21 @@ const (
 	// Keywords
 	FUNCTION = "FUNCTION"
 	LET      = "LET"
+	TRUE     = "TRUE"
+	FALSE    = "FALSE"
+	IF       = "IF"
+	ELSE     = "ELSE"
+	RETURN   = "RETURN"
 )
 
 var keywords = map[string]TokenType{
-	"fn":  FUNCTION,
-	"let": LET,
+	"fn":     FUNCTION,
+	"let":    LET,
+	"true":   TRUE,
+	"false":  FALSE,
+	"if":     IF,
+	"else":   ELSE,
+	"return": RETURN,
 }
 
 func LookupIdent(ident string) TokenType {