From d4d6561c6f34542e4849ced5c1bac8ad70dc523c Mon Sep 17 00:00:00 2001
From: Tyrel Souza <tyrel@tyrelsouza.com>
Date: Wed, 1 Dec 2021 15:31:30 -0500
Subject: [PATCH] ast LET statements

---
 .gitignore            |   1 +
 ast/ast.go            |  46 ++++++++++++++++++
 parser/parser.go      | 106 ++++++++++++++++++++++++++++++++++++++++++
 parser/parser_test.go |  76 ++++++++++++++++++++++++++++++
 4 files changed, 229 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 ast/ast.go
 create mode 100644 parser/parser.go
 create mode 100644 parser/parser_test.go

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..d992b6f
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+Session.vim
diff --git a/ast/ast.go b/ast/ast.go
new file mode 100644
index 0000000..d3180a9
--- /dev/null
+++ b/ast/ast.go
@@ -0,0 +1,46 @@
+package ast
+
+import "gitlab.com/Tyrel/monkey/token"
+
+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()
+	} else {
+		return ""
+	}
+}
+
+type LetStatement struct {
+	Token token.Token
+	Name  *Identifier
+	Value Expression
+}
+
+func (ls *LetStatement) statementNode()       {}
+func (ls *LetStatement) TokenLiteral() string { return ls.Token.Literal }
+
+type Identifier struct {
+	Token token.Token
+	Value string
+}
+
+func (ls *Identifier) expressionNode()      {}
+func (ls *Identifier) TokenLiteral() string { return ls.Token.Literal }
diff --git a/parser/parser.go b/parser/parser.go
new file mode 100644
index 0000000..7ea24ca
--- /dev/null
+++ b/parser/parser.go
@@ -0,0 +1,106 @@
+package parser
+
+import (
+	"fmt"
+
+	"gitlab.com/Tyrel/monkey/ast"
+	"gitlab.com/Tyrel/monkey/lexer"
+	"gitlab.com/Tyrel/monkey/token"
+)
+
+type Parser struct {
+	l *lexer.Lexer
+
+	curToken  token.Token
+	peekToken token.Token
+
+	errors []string
+}
+
+func New(l *lexer.Lexer) *Parser {
+	p := &Parser{
+		l:      l,
+		errors: []string{},
+	}
+
+	// get two tokens to curToken and peekToken are set
+	p.nextToken()
+	p.nextToken()
+
+	return p
+}
+
+func (p *Parser) Errors() []string {
+	return p.errors
+}
+
+func (p *Parser) nextToken() {
+	p.curToken = p.peekToken
+	p.peekToken = p.l.NextToken()
+}
+
+func (p *Parser) ParseProgram() *ast.Program {
+	program := &ast.Program{}
+	program.Statements = []ast.Statement{}
+
+	for p.curToken.Type != token.EOF {
+		stmt := p.parseStatement()
+		if stmt != nil {
+			program.Statements = append(program.Statements, stmt)
+		}
+		p.nextToken()
+	}
+	return program
+}
+
+func (p *Parser) parseStatement() ast.Statement {
+	switch p.curToken.Type {
+	case token.LET:
+		return p.parseLetStatement()
+	default:
+		return nil
+	}
+
+}
+
+func (p *Parser) parseLetStatement() *ast.LetStatement {
+	stmt := &ast.LetStatement{Token: p.curToken}
+
+	if !p.expectPeek(token.IDENT) {
+		return nil
+	}
+
+	stmt.Name = &ast.Identifier{Token: p.curToken, Value: p.curToken.Literal}
+
+	if !p.expectPeek(token.ASSIGN) {
+		return nil
+	}
+
+	for !p.curTokenIs(token.SEMICOLON) {
+		p.nextToken()
+	}
+
+	return stmt
+
+}
+
+func (p *Parser) curTokenIs(t token.TokenType) bool {
+	return p.curToken.Type == t
+}
+func (p *Parser) peekTokenIs(t token.TokenType) bool {
+	return p.peekToken.Type == t
+}
+func (p *Parser) expectPeek(t token.TokenType) bool {
+	if p.peekTokenIs(t) {
+		p.nextToken()
+		return true
+	} else {
+		p.peekError(t)
+		return false
+	}
+}
+
+func (p *Parser) peekError(t token.TokenType) {
+	msg := fmt.Sprintf("expected next token to be %s. got=%s", 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..890849b
--- /dev/null
+++ b/parser/parser_test.go
@@ -0,0 +1,76 @@
+package parser
+
+import (
+	"testing"
+
+	"gitlab.com/Tyrel/monkey/ast"
+	"gitlab.com/Tyrel/monkey/lexer"
+)
+
+func TestLetStatements(t *testing.T) {
+	input := `
+let x 5;
+let y = 10;
+let 838383;
+`
+	l := lexer.New(input)
+	p := New(l)
+
+	program := p.ParseProgram()
+	if program == nil {
+		t.Fatalf("ParseProgram() return nil")
+	}
+	if len(program.Statements) != 3 {
+		t.Fatalf("program.Statements does not contain 3 statements. got=%d",
+			len(program.Statements))
+	}
+
+	checkParserErrors(t, p)
+
+	tests := []struct {
+		expectedIdentifier string
+	}{
+		{"x"},
+		{"y"},
+		{"foobar"},
+	}
+
+	for i, tt := range tests {
+		stmt := program.Statements[i]
+		if !testLetStatement(t, stmt, tt.expectedIdentifier) {
+			return
+		}
+	}
+}
+
+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
+	}
+	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)
+		return false
+	}
+	return true
+}
+
+func checkParserErrors(t *testing.T, p *Parser) {
+	errors := p.Errors()
+	if len(errors) == 0 {
+		return
+	}
+
+	t.Errorf("parser had %d errors", len(errors))
+	for _, msg := range errors {
+		t.Errorf("parser error: %q", msg)
+	}
+	t.FailNow()
+
+}