z

ast/ast.go

@@ -0,0 +1,27 @@
+package ast
+
+type Node interface {
+	TokenLiteral() string
+}
+
+type Statement interface {
+	Node
+	statementNode()
+}
+
+type Expression interface {
+	Node
+	expressionNode()
+}
+
+type Program struct {
+	Statements []Statement
+}
+
+func (p *Program) TokenLiteral() string {
+	if len(p.Statements) > 0 {
+		return p.Statements[0].TokenLiteral()
+	}
+
+	return ""
+}

go.mod

@@ -0,0 +1,3 @@
+module gointerpreter
+
+go 1.22.0

lexer/lexer.go

@@ -0,0 +1,142 @@
+package lexer
+
+import "gointerpreter/token"
+
+type Lexer struct {
+	input        string
+	position     int  // current position in input (current char)
+	readPosition int  // current reading position in input (after current char)
+	ch           byte // current char under examination
+}
+
+func New(input string) *Lexer {
+	l := &Lexer{input: input}
+	l.readChar()
+	return l
+}
+
+func (l *Lexer) readChar() {
+	if l.readPosition >= len(l.input) {
+		l.ch = 0
+	} else {
+		l.ch = l.input[l.readPosition]
+	}
+
+	l.position = l.readPosition
+	l.readPosition += 1
+}
+
+func (l *Lexer) peekChar() byte {
+	if l.readPosition >= len(l.input) {
+		return 0
+	}
+
+	return l.input[l.readPosition]
+}
+
+func (l *Lexer) NextToken() token.Token {
+	var tok token.Token
+
+	l.skipWhitespaces()
+
+	switch l.ch {
+	case '=':
+		if l.peekChar() == '=' {
+			ch := l.ch
+			l.readChar()
+			literal := string(ch) + string(l.ch)
+			tok = token.Token{Literal: literal, Type: token.EQ}
+		} else {
+			tok = newToken(token.ASSIGN, l.ch)
+		}
+	case '{':
+		tok = newToken(token.LBRACE, l.ch)
+	case '}':
+		tok = newToken(token.RBRACE, l.ch)
+	case '(':
+		tok = newToken(token.LPAREN, l.ch)
+	case ')':
+		tok = newToken(token.RPAREN, l.ch)
+	case ';':
+		tok = newToken(token.SEMICOLON, l.ch)
+	case ',':
+		tok = newToken(token.COMMA, 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{Literal: literal, Type: token.NOT_EQ}
+		} else {
+			tok = newToken(token.BANG, l.ch)
+		}
+	case '*':
+		tok = newToken(token.ASTERISK, l.ch)
+	case '/':
+		tok = newToken(token.SLASH, l.ch)
+	case '>':
+		tok = newToken(token.GT, l.ch)
+	case '<':
+		tok = newToken(token.LT, 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)
+		}
+	}
+
+	l.readChar()
+	return tok
+}
+
+func (l *Lexer) readNumber() string {
+	position := l.position
+
+	for isDigit(l.ch) {
+		l.readChar()
+	}
+
+	return l.input[position:l.position]
+}
+
+func (l *Lexer) readIdentifier() string {
+	position := l.position
+
+	for isLetter(l.ch) {
+		l.readChar()
+	}
+
+	return l.input[position:l.position]
+}
+
+func (l *Lexer) skipWhitespaces() {
+	for l.ch == ' ' || l.ch == '\t' || l.ch == '\n' || l.ch == '\r' {
+		l.readChar()
+	}
+}
+
+func isLetter(ch byte) bool {
+	return 'a' <= ch && 'z' >= ch || 'A' <= ch && 'Z' >= ch || ch == '_'
+}
+
+func isDigit(ch byte) bool {
+	return '0' <= ch && '9' >= ch
+}
+
+func newToken(tokenType token.TokenType, ch byte) token.Token {
+	return token.Token{Type: tokenType, Literal: string(ch)}
+}

lexer/lexer_test.go

@@ -0,0 +1,122 @@
+package lexer
+
+import (
+	"gointerpreter/token"
+	"testing"
+)
+
+func TestNextToken(t *testing.T) {
+	input := `
+    let five = 5;
+    let ten = 10;
+
+    let add = fn(x, y) {
+        x + y;
+    }
+
+    let result = add(five, ten);
+    !-/*5;
+    5 < 10 > 5;
+
+    if 5 > 10 {
+        return true;
+    } else {
+        return false;
+    }
+
+    10 == 10;
+    5 != 10;
+    `
+
+	tests := []struct {
+		expectedType    token.TokenType
+		expectedLiteral string
+	}{
+		{token.LET, "let"},
+		{token.IDENT, "five"},
+		{token.ASSIGN, "="},
+		{token.INT, "5"},
+		{token.SEMICOLON, ";"},
+		{token.LET, "let"},
+		{token.IDENT, "ten"},
+		{token.ASSIGN, "="},
+		{token.INT, "10"},
+		{token.SEMICOLON, ";"},
+		{token.LET, "let"},
+		{token.IDENT, "add"},
+		{token.ASSIGN, "="},
+		{token.FUNCTION, "fn"},
+		{token.LPAREN, "("},
+		{token.IDENT, "x"},
+		{token.COMMA, ","},
+		{token.IDENT, "y"},
+		{token.RPAREN, ")"},
+		{token.LBRACE, "{"},
+		{token.IDENT, "x"},
+		{token.PLUS, "+"},
+		{token.IDENT, "y"},
+		{token.SEMICOLON, ";"},
+		{token.RBRACE, "}"},
+		{token.LET, "let"},
+		{token.IDENT, "result"},
+		{token.ASSIGN, "="},
+		{token.IDENT, "add"},
+		{token.LPAREN, "("},
+		{token.IDENT, "five"},
+		{token.COMMA, ","},
+		{token.IDENT, "ten"},
+		{token.RPAREN, ")"},
+		{token.SEMICOLON, ";"},
+		{token.BANG, "!"},
+		{token.MINUS, "-"},
+		{token.SLASH, "/"},
+		{token.ASTERISK, "*"},
+		{token.INT, "5"},
+		{token.SEMICOLON, ";"},
+		{token.INT, "5"},
+		{token.LT, "<"},
+		{token.INT, "10"},
+		{token.GT, ">"},
+		{token.INT, "5"},
+		{token.SEMICOLON, ";"},
+		{token.IF, "if"},
+		{token.INT, "5"},
+		{token.GT, ">"},
+		{token.INT, "10"},
+		{token.LBRACE, "{"},
+		{token.RETURN, "return"},
+		{token.TRUE, "true"},
+		{token.SEMICOLON, ";"},
+		{token.RBRACE, "}"},
+		{token.ELSE, "else"},
+		{token.LBRACE, "{"},
+		{token.RETURN, "return"},
+		{token.FALSE, "false"},
+		{token.SEMICOLON, ";"},
+		{token.RBRACE, "}"},
+		{token.INT, "10"},
+		{token.EQ, "=="},
+		{token.INT, "10"},
+		{token.SEMICOLON, ";"},
+		{token.INT, "5"},
+		{token.NOT_EQ, "!="},
+		{token.INT, "10"},
+		{token.SEMICOLON, ";"},
+
+		{token.EOF, ""},
+	}
+
+	l := New(input)
+
+	for i, tt := range tests {
+		tok := l.NextToken()
+
+		if tok.Type != tt.expectedType {
+			t.Fatalf("test[%d] - tokentype wrong, expected [%q], got [%q]", i, tt.expectedType, tok.Type)
+		}
+
+		if tok.Literal != tt.expectedLiteral {
+			t.Fatalf("test[%d] - tokenliteral wrong, expected [%q], got [%q]", i, tt.expectedLiteral, tok.Literal)
+		}
+	}
+}

main.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"fmt"
+	"gointerpreter/repl"
+	"os"
+	"os/user"
+)
+
+func main() {
+	user, err := user.Current()
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Printf("Hello %s! This is the gointerpreter programming language!\n", user.Username)
+	fmt.Printf("Type in commands\n")
+	repl.Start(os.Stdin, os.Stdout)
+}

repl/repl.go

@@ -0,0 +1,31 @@
+package repl
+
+import (
+	"bufio"
+	"fmt"
+	"gointerpreter/lexer"
+	"gointerpreter/token"
+	"io"
+)
+
+const PROMPT = ">> "
+
+func Start(in io.Reader, out io.Writer) {
+	scanner := bufio.NewScanner(in)
+
+	for {
+		fmt.Fprintf(out, 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.Fprintf(out, "%+v\n", tok)
+		}
+	}
+}

token/token.go

@@ -0,0 +1,67 @@
+package token
+
+type TokenType string
+
+type Token struct {
+	Type    TokenType
+	Literal string
+}
+
+const (
+	ILLEGAL = "ILLEGAL"
+	EOF     = "EOF"
+
+	// identifiers + literals
+	IDENT = "IDENT"
+	INT   = "INT"
+
+	// operators
+	PLUS     = "+"
+	MINUS    = "-"
+	ASSIGN   = "="
+	BANG     = "!"
+	ASTERISK = "*"
+	SLASH    = "/"
+
+	EQ     = "=="
+	NOT_EQ = "!="
+
+	// delimiters
+	COMMA     = ","
+	SEMICOLON = ";"
+
+	LPAREN = "("
+	RPAREN = ")"
+	LBRACE = "{"
+	RBRACE = "}"
+
+	LT = "<"
+	GT = ">"
+
+	// keywords
+	FUNCTION = "function"
+	LET      = "let"
+	IF       = "if"
+	ELSE     = "else"
+	TRUE     = "true"
+	FALSE    = "false"
+	RETURN   = "return"
+)
+
+var keywords = map[string]TokenType{
+	"fn":     FUNCTION,
+	"let":    LET,
+	"return": RETURN,
+	"if":     IF,
+	"else":   ELSE,
+	"true":   TRUE,
+	"false":  FALSE,
+}
+
+func LookupIdent(ident string) TokenType {
+	if tt, ok := keywords[ident]; ok {
+		return tt
+	}
+
+	return IDENT
+}