parser:let|ident

6 files changed, 242 insertions, 17 deletions

diff --git a/lexer/lexer.go b/lexer/lexer.go
index b65d00b..589ed60 100644
--- a/lexer/lexer.go
+++ b/lexer/lexer.go
@@ -1,4 +1,5 @@
 package lexer
+
 import "mana/tokens"
 
 type Lexer struct {
@@ -10,7 +11,7 @@ type Lexer struct {
 
 // New returns a new Lexer instance.
 func New(input string) *Lexer {
-	l := &Lexer{input: input}
+	var l *Lexer = &Lexer{input: input}
 	l.readChar()
 	return l
 }
@@ -24,9 +25,9 @@ func (l *Lexer) NextToken() tokens.Token {
 	switch l.ch {
 	case '=':
 		if l.peekChar() == '=' {
-			ch := l.ch
+			var ch byte = l.ch
 			l.readChar()
-			literal := string(ch) + string(l.ch)
+			var literal string = string(ch) + string(l.ch)
 			tok = tokens.Token{Type: tokens.EQ, Literal: literal}
 		} else {
 			tok = newToken(tokens.ASSIGN, l.ch)
@@ -45,9 +46,9 @@ func (l *Lexer) NextToken() tokens.Token {
 		tok = newToken(tokens.GT, l.ch)
 	case '!':
 		if l.peekChar() == '=' {
-			ch := l.ch
+			var ch byte = l.ch
 			l.readChar()
-			literal := string(ch) + string(l.ch)
+			var literal string = string(ch) + string(l.ch)
 			tok = tokens.Token{Type: tokens.NOT_EQ, Literal: literal}
 		} else {
 			tok = newToken(tokens.BANG, l.ch)
@@ -80,7 +81,7 @@ func (l *Lexer) NextToken() tokens.Token {
 			tok = newToken(tokens.ILLEGAL, l.ch)
 		}
 	}
-	
+
 	l.readChar()
 	return tok
 }
@@ -129,7 +130,7 @@ func (l *Lexer) peekChar() byte {
 
 // readIdentifier reads an identifier and advances the position in the input string until it encounters a non-letter character.
 func (l *Lexer) readIdentifier() string {
-	position := l.position
+	var position int = l.position
 	for isLetter(l.ch) {
 		l.readChar()
 	}
@@ -138,7 +139,7 @@ func (l *Lexer) readIdentifier() string {
 
 // readNumber reads a number and advances the position in the input string until it encounters a non-digit character.
 func (l *Lexer) readNumber() string {
-	position := l.position
+	var position int = l.position
 	for isDigit(l.ch) {
 		l.readChar()
 	}
diff --git a/lexer/lexer_test.go b/lexer/lexer_test.go
index f8e3eae..5cce79d 100644
--- a/lexer/lexer_test.go
+++ b/lexer/lexer_test.go
@@ -6,7 +6,7 @@ import (
 )
 
 func TestNextToken(t *testing.T) {
-	input := `
+	const input string = `
 		let five = 5;
 		let ten = 10;
 
@@ -29,7 +29,7 @@ func TestNextToken(t *testing.T) {
 		10 != 9;
 	`
 
-	tests := []struct {
+	var tests = []struct {
 		expectedType    tokens.TokenType
 		expectedLiteral string
 	}{
@@ -109,10 +109,11 @@ func TestNextToken(t *testing.T) {
 		{tokens.EOF, ""},
 	}
 
-	l := New(input)
+
+	var l *Lexer = New(input)
 
 	for i, tt := range tests {
-		tok := l.NextToken()
+		var tok tokens.Token = l.NextToken()
 
 		if tok.Type != tt.expectedType {
 			t.Fatalf("tests[%d] - tokentype wrong. expected=%q, got=%q",
diff --git a/main.go b/main.go
index deba212..92962bf 100644
--- a/main.go
+++ b/main.go
@@ -8,7 +8,7 @@ import (
 )
 
 func main() {
-	user, err := user.Current()
+	var user, err = user.Current()
 
 	if err != nil {
 		panic(err)
diff --git a/parser/parser.go b/parser/parser.go
new file mode 100644
index 0000000..6e8bba6
--- /dev/null
+++ b/parser/parser.go
@@ -0,0 +1,132 @@
+package parser
+
+import (
+	"fmt"
+	"mana/ast"
+	"mana/lexer"
+	"mana/tokens"
+)
+
+// Parser represents a parser.
+type Parser struct {
+	l *lexer.Lexer
+
+	curToken  tokens.Token
+	peekToken tokens.Token
+
+	errors []string
+}
+
+// New returns a new Parser.
+func New(l *lexer.Lexer) *Parser {
+	var p *Parser = &Parser{
+		l: l,
+		errors: []string{},
+	}
+
+	// Read two tokens, so curToken and peekToken are both set.
+	p.nextToken()
+	p.nextToken()
+
+	return p
+}
+
+// nextToken advances the tokens.
+func (p *Parser) nextToken() {
+	p.curToken = p.peekToken
+	p.peekToken = p.l.NextToken()
+}
+
+// ParseProgram parses a program.
+func (p *Parser) ParseProgram() *ast.Program {
+
+	// Initialize the program with an empty slice of statements.
+	var program *ast.Program = &ast.Program{}
+	program.Statements = []ast.Statement{}
+
+	// Iterate over the tokens until we reach the end of file.
+	for p.curToken.Type != tokens.EOF {
+		// Parse the statement and append it to the program.
+		var stmt ast.Statement = p.parseStatement()
+
+		if stmt != nil {
+			program.Statements = append(program.Statements, stmt)
+		}
+
+		// Advance to the next token.
+		p.nextToken()
+	}
+
+	// Return the program.
+	return program
+}
+
+// parseStatement parses a statement.
+func (p *Parser) parseStatement() ast.Statement {
+	switch p.curToken.Type {
+	case tokens.LET:
+		return p.parseLetStatement()
+	default:
+		return nil
+	}
+}
+
+// parseLetStatement parses a let statement.
+func (p *Parser) parseLetStatement() *ast.LetStatement {
+	var stmt *ast.LetStatement = &ast.LetStatement{Token: p.curToken}
+
+	if !p.expectPeek(tokens.IDENT) {
+		return nil
+	}
+
+	stmt.Name = &ast.Identifier{Token: p.curToken, Value: p.curToken.Literal}
+
+	if !p.expectPeek(tokens.ASSIGN) {
+		return nil
+	}
+
+	// TODO: We're skipping the expressions until we
+	// encounter a semicolon.
+
+	for !p.curTokenIs(tokens.SEMICOLON) {
+		p.nextToken()
+	}
+
+	return stmt
+}
+
+// curTokenIs returns true if the current token is of the given type.
+func (p *Parser) curTokenIs(t tokens.TokenType) bool {
+	return p.curToken.Type == t
+}
+
+// peekTokenIs returns true if the next token is of the given type.
+func (p *Parser) peekTokenIs(t tokens.TokenType) bool {
+	return p.peekToken.Type == t
+}
+
+// expectPeek expects the next token to be of the given type.
+func (p *Parser) expectPeek(t tokens.TokenType) bool {
+	if p.peekTokenIs(t) {
+		p.nextToken()
+
+		return true
+	} else {
+		p.peekError(t)
+		
+		return false
+	}
+}
+
+// Errors returns the parser errors.
+func (p *Parser) Errors() []string {
+	return p.errors
+}
+
+// peekError returns an error message.
+func (p *Parser) peekError(t tokens.TokenType) {
+	var msg string = fmt.Sprintf("expected next token to be %s, got %s instead", t, p.peekToken.Type)
+
+	p.errors = append(p.errors, msg)
+}
+
diff --git a/parser/parser_test.go b/parser/parser_test.go
new file mode 100644
index 0000000..8f78c8b
--- /dev/null
+++ b/parser/parser_test.go
@@ -0,0 +1,91 @@
+package parser
+
+import (
+	"testing"
+	"mana/ast"
+	"mana/lexer"
+)
+
+func TestLetStatements(t *testing.T) {
+	const input string = `
+		let x = 5;
+		let y = 10;
+		let foobar = 838383;
+	`
+
+	var l *lexer.Lexer = lexer.New(input)
+	var p *Parser = New(l)
+
+	var program *ast.Program = p.ParseProgram()
+	checkParserErrors(t, p)
+
+	if program == nil {
+		t.Fatalf("ParseProgram() returned nil")
+	}
+
+	if len(program.Statements) != 3 {
+		t.Fatalf("program.Statements does not contain 3 statements. got=%d", len(program.Statements))
+	}
+
+	var tests = []struct {
+		expectedIdentifier string
+	}{
+		{"x"},
+		{"y"},
+		{"foobar"},
+	}
+
+	for i, tt := range tests {
+		var stmt ast.Statement = program.Statements[i]
+
+		if !testLetStatement(t, stmt, tt.expectedIdentifier) {
+			return
+		}
+	}
+}
+
+func checkParserErrors(t *testing.T, p *Parser) {
+	var errors []string = p.Errors()
+
+	if len(errors) == 0 {
+		return
+	}
+
+	t.Errorf("parser has %d errors", len(errors))
+
+	for _, msg := range errors {
+		t.Errorf("parser error: %q", msg)
+	}
+
+	t.FailNow()
+}
+
+func testLetStatement(t *testing.T, s ast.Statement, name string) bool {
+	if s.TokenLiteral() != "let" {
+		t.Errorf("s.TokenLiteral not 'let'. got=%q", s.TokenLiteral())
+
+		return false
+	}
+
+	var letStmt, ok = s.(*ast.LetStatement)
+
+	if !ok {
+		t.Errorf("s not *ast.LetStatement. got=%T", s)
+
+		return false
+	}
+
+	if letStmt.Name.Value != name {
+		t.Errorf("letStmt.Name.Value not '%s'. got=%s", name, letStmt.Name.Value)
+
+		return false
+	}
+
+	if letStmt.Name.TokenLiteral() != name {
+		t.Errorf("letStmt.Name.TokenLiteral() not '%s'. got=%s", name, letStmt.Name.TokenLiteral())
+
+		return false
+	}
+
+	return true
+}
diff --git a/repl/repl.go b/repl/repl.go
index 37acd49..0002a89 100644
--- a/repl/repl.go
+++ b/repl/repl.go
@@ -12,18 +12,18 @@ import (
 const PROMPT = "=> "
 
 func Start(in io.Reader, out io.Writer) {
-	scanner := bufio.NewScanner(in)
+	var scanner *bufio.Scanner = bufio.NewScanner(in)
 
 	for {
 		fmt.Fprint(out, PROMPT)
-		scanned := scanner.Scan()
+		var scanned bool = scanner.Scan()
 		
 		if !scanned {
 			return
 		}
 
-		line := scanner.Text()
-		l := lexer.New(line)
+		var line string = scanner.Text()
+		var l *lexer.Lexer = lexer.New(line)
 
 		for tok := l.NextToken(); tok.Type != tokens.EOF; tok = l.NextToken() {
 			fmt.Fprintf(out, "%+v\n", tok)