From 7abb78c88e75a9edebb11ee4014bf5ae0755ca58 Mon Sep 17 00:00:00 2001
From: 54L1M <themhsalimi@gmail.com>
Date: Mon, 29 Jan 2024 02:12:19 +0330
Subject: [PATCH] parse var statements

---
 ast/ast.go            |  6 ++--
 parser/parser.go      | 81 +++++++++++++++++++++++++++++++++++++++++--
 parser/parser_test.go | 78 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 160 insertions(+), 5 deletions(-)
 create mode 100644 parser/parser_test.go

diff --git a/ast/ast.go b/ast/ast.go
index 00159e9..ec1d1b5 100644
--- a/ast/ast.go
+++ b/ast/ast.go
@@ -40,13 +40,13 @@ func (i *Identifier) TokenLiteral() string {
 	return i.Token.Literal
 }
 
-type LetStatement struct {
+type VarStatement struct {
 	Token token.Token
 	Name  *Identifier
 	Value Expression
 }
 
-func (ls *LetStatement) statementNode() {}
-func (ls *LetStatement) TokenLiteral() string {
+func (ls *VarStatement) statementNode() {}
+func (ls *VarStatement) TokenLiteral() string {
 	return ls.Token.Literal
 }
diff --git a/parser/parser.go b/parser/parser.go
index aec6b00..9f4a211 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -1,6 +1,8 @@
 package parser
 
 import (
+	"fmt"
+
 	"github.com/54L1m/mil-lang/ast"
 	"github.com/54L1m/mil-lang/lexer"
 	"github.com/54L1m/mil-lang/token"
@@ -9,23 +11,98 @@ import (
 type Parser struct {
 	l *lexer.Lexer
 
+	errors []string
+
 	curToken  token.Token
 	peekToken token.Token
 }
 
 func New(l *lexer.Lexer) *Parser {
-	p := &Parser{l: l}
+	p := &Parser{
+		l:      l,
+		errors: []string{},
+	}
 
 	p.nextToken()
 	p.nextToken()
 	return p
 }
 
+func (p *Parser) Errors() []string {
+	return p.errors
+}
+
+func (p *Parser) peekError(t token.TokenType) {
+	msg := fmt.Sprintf("expected next token to be %s, got %s instead",
+		t, p.peekToken.Type)
+	p.errors = append(p.errors, msg)
+}
+
 func (p *Parser) nextToken() {
 	p.curToken = p.peekToken
 	p.peekToken = p.l.NextToken()
 }
 
 func (p *Parser) ParseProgram() *ast.Program {
-	return nil
+	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.VAR:
+		return p.parseVarStatement()
+	default:
+		return nil
+
+	}
+}
+
+func (p *Parser) parseVarStatement() *ast.VarStatement {
+	stmt := &ast.VarStatement{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
+	}
+
+	//TODO: We're skipping the expressions until we encounter a semicolon
+
+	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
+	}
 }
diff --git a/parser/parser_test.go b/parser/parser_test.go
new file mode 100644
index 0000000..4a6a693
--- /dev/null
+++ b/parser/parser_test.go
@@ -0,0 +1,78 @@
+package parser
+
+import (
+	"testing"
+
+	"github.com/54L1m/mil-lang/ast"
+	"github.com/54L1m/mil-lang/lexer"
+)
+
+func TestLetStatement(t *testing.T) {
+	input := `
+	var x = 5;
+	var y = 10;
+	var foobar = 838383;
+	`
+	l := lexer.New(input)
+	p := New(l)
+
+	program := p.ParseProgram()
+	checkParseErrors(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))
+	}
+
+	tests := []struct {
+		expectedIdentifier string
+	}{
+		{"x"},
+		{"y"},
+		{"foobar"},
+	}
+
+	for i, tt := range tests {
+		stmt := program.Statements[i]
+		if !testVarStatement(t, stmt, tt.expectedIdentifier) {
+			return
+		}
+	}
+}
+
+func testVarStatement(t *testing.T, s ast.Statement, name string) bool {
+	if s.TokenLiteral() != "var" {
+		t.Errorf("s.TokenLiteral not 'var'. got=%q", s.TokenLiteral())
+		return false
+	}
+	varStmt, ok := s.(*ast.VarStatement)
+	if !ok {
+		t.Errorf("s not *ast.VarStatement. got=%T", s)
+		return false
+	}
+	if varStmt.Name.Value != name {
+		t.Errorf("letStmt.Name.Value not '%s'. got=%s", name, varStmt.Name.Value)
+		return false
+	}
+	if varStmt.Name.TokenLiteral() != name {
+		t.Errorf("letStmt.Name.TokenLiteral() not '%s'. got=%s",
+			name, varStmt.Name.TokenLiteral())
+		return false
+	}
+	return true
+}
+
+func checkParseErrors(t *testing.T, p *Parser) {
+	errors := 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()
+}