init interpreter

Author: jmelahman

projects/interpreter/go.mod

@@ -0,0 +1,3 @@
+module jmelahman/interpreter
+
+go 1.23.0

projects/interpreter/lexer/lexer.go

@@ -0,0 +1,59 @@
+package lexer
+
+import "jmelahman/interpreter/token"
+
+type Lexer struct {
+	input        string
+	position     int
+	readPosition int
+	ch           byte
+}
+
+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++
+}
+
+func (l *Lexer) NextToken() token.Token {
+	var tok token.Token
+
+	switch l.ch {
+	case '=':
+		tok = newToken(token.ASSIGN, 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:
+		tok.Literal = ""
+		tok.Type = token.EOF
+	}
+
+	l.readChar()
+	return tok
+}
+
+func newToken(tokenType token.TokenType, ch byte) token.Token {
+	return token.Token{Type: tokenType, Literal: string(ch)}
+}

projects/interpreter/lexer/lexer_test.go

@@ -0,0 +1,38 @@
+package lexer
+
+import (
+	"jmelahman/interpreter/token"
+	"testing"
+)
+
+func TestNextToken(t *testing.T) {
+	input := `=+(){},;`
+
+	tests := []struct {
+		expectedType    token.TokenType
+		expectedLiteral string
+	}{
+		{token.ASSIGN, "="},
+		{token.PLUS, "+"},
+		{token.LPAREN, "("},
+		{token.RPAREN, ")"},
+		{token.LBRACE, "{"},
+		{token.RBRACE, "}"},
+		{token.COMMA, ","},
+		{token.SEMICOLON, ";"},
+		{token.EOF, ""},
+	}
+
+	l := New(input)
+
+	for i, tt := range tests {
+		tok := l.NextToken()
+
+		if tok.Type != tt.expectedType {
+			t.Fatalf("tests[%d] - tokentype wrong. expected=%q, got=%q", i, tt.expectedType, tok.Type)
+		}
+		if tok.Literal != tt.expectedLiteral {
+			t.Fatalf("tests[%d] - literal wrong. expected=%q, got=%q", i, tt.expectedLiteral, tok.Literal)
+		}
+	}
+}

projects/interpreter/token/token.go

@@ -0,0 +1,34 @@
+package token
+
+type TokenType string
+
+type Token struct {
+	Type    TokenType
+	Literal string
+}
+
+const (
+	ILLEGAL = "ILLEGAL"
+	EOF     = "EOF"
+
+	// Identifiers + literals
+	IDENT = "IDENT"
+	INT   = "INT"
+
+	// Operators
+	ASSIGN = "="
+	PLUS   = "+"
+
+	// Delimiters
+	COMMA     = ","
+	SEMICOLON = ";"
+
+	LPAREN = "("
+	RPAREN = ")"
+	LBRACE = "{"
+	RBRACE = "}"
+
+	// Keywords
+	FUNCTION = "FUNCTION"
+	LET      = "LET"
+)