parsing var statements!!

ast/ast.go

@@ -0,0 +1,46 @@
+package ast
+
+import "github.com/Jonak-Adipta-Kalita/JAK-Programming-Language/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 VarStatement struct {
+	Token token.Token
+	Name *Identifier
+	Value Expression
+}
+
+func (ls *VarStatement) statementNode() {}
+
+func (ls *VarStatement) TokenLiteral() string { return ls.Token.Literal }
+
+type Identifier struct {
+	Token token.Token
+	Value string
+}
+
+func (i *Identifier) expressionNode() {}
+
+func (i *Identifier) TokenLiteral() string { return i.Token.Literal }

parser/parser.go

@@ -0,0 +1,85 @@
+package parser
+
+import (
+	"github.com/Jonak-Adipta-Kalita/JAK-Programming-Language/ast"
+	"github.com/Jonak-Adipta-Kalita/JAK-Programming-Language/lexer"
+	"github.com/Jonak-Adipta-Kalita/JAK-Programming-Language/token"
+)
+
+type Parser struct {
+	l         *lexer.Lexer
+	curToken  token.Token
+	peekToken token.Token
+}
+
+func New(l *lexer.Lexer) *Parser {
+	p := &Parser{l: l}
+	p.nextToken()
+	p.nextToken()
+	return p
+}
+
+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.VAR:
+			return p.parseVarStatement()
+		default:
+			return nil
+	}
+}
+
+func (p *Parser) parseVarStatement() *ast.VarStatement {
+	stmt := &ast.VarStatement{Token: p.curToken}
+	if !p.expectPeek(token.IDENTIFIER) {
+		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 {
+		return false
+	}
+}	

parser/parser_test.go

@@ -0,0 +1,70 @@
+package parser
+
+import (
+	"testing"
+
+	"github.com/Jonak-Adipta-Kalita/JAK-Programming-Language/ast"
+	"github.com/Jonak-Adipta-Kalita/JAK-Programming-Language/lexer"
+)
+func TestVarStatements(t *testing.T) {
+	input := `
+	var x = 5;
+	var y = 10;
+	var foobar = 838383;
+	`
+
+	l := lexer.New(input)
+	p := New(l)
+
+	program := p.ParseProgram()
+
+	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("varStmt.Name.Value not '%s'. got=%s", name, varStmt.Name.Value)
+		return false
+	}
+
+	if varStmt.Name.TokenLiteral() != name {
+		t.Errorf("s.Name not '%s'. got=%s", name, varStmt.Name)
+		return false
+	}
+
+	return true
+}