reassign values

parser/parser.go

@@ -127,6 +127,11 @@ func (p *Parser) noPrefixParseFnError(t token.TokenType) {
 	p.errors = append(p.errors, msg)
 }
 
+func (p *Parser) noInfixParseFnError(t token.TokenType) {
+	msg := fmt.Sprintf("no infix parse function for %s found", t)
+	p.errors = append(p.errors, msg)
+}
+
 func (p *Parser) ParseProgram() *ast.Program {
 	program := &ast.Program{}
 	program.Statements = []ast.Statement{}
@@ -143,6 +148,10 @@ func (p *Parser) ParseProgram() *ast.Program {
 }
 
 func (p *Parser) parseStatement() ast.Statement {
+	if p.peekToken.Type == token.ASSIGN {
+		return p.parseAssignmentStatement()
+	}
+
 	switch p.curToken.Type {
 	case token.LET:
 		return p.parseLetStatement()
@@ -218,7 +227,8 @@ func (p *Parser) parseExpression(precedence int) ast.Expression {
 	for !p.peekTokenIs(token.SEMICOLON) && precedence < p.peekPrecedence() {
 		infix := p.infixParseFns[p.peekToken.Type]
 		if infix == nil {
-			return leftExp
+			p.noInfixParseFnError(p.peekToken.Type)
+			//return leftExp
 		}
 
 		p.nextToken()
@@ -516,3 +526,19 @@ func (p *Parser) parseWhileExpression() ast.Expression {
 
 	return expression
 }
+
+func (p *Parser) parseAssignmentStatement() ast.Statement {
+	stmt := &ast.AssignmentStatement{Token: p.peekToken}
+	stmt.Name = &ast.Identifier{Token: p.curToken, Value: p.curToken.Literal}
+
+	p.nextToken()
+	p.nextToken()
+
+	stmt.Value = p.parseExpression(LOWEST)
+
+	if p.peekTokenIs(token.SEMICOLON) {
+		p.nextToken()
+	}
+
+	return stmt
+}

parser/parser_test.go

@@ -921,6 +921,40 @@ func TestWhileExpression(t *testing.T) {
 	}
 }
 
+func TestAssignmentStatements(t *testing.T) {
+	tests := []struct {
+		input              string
+		expectedIdentifier string
+		expectedValue      interface{}
+	}{
+		{"x = 5;", "x", 5},
+		{"y = true;", "y", true},
+		{"foobar = y;", "foobar", "y"},
+	}
+
+	for _, tt := range tests {
+		l := lexer.New(tt.input)
+		p := New(l)
+		program := p.ParseProgram()
+		checkParserErrors(t, p)
+
+		if len(program.Statements) != 1 {
+			t.Fatalf("program.Statements does not contain 1 statements. got=%d",
+				len(program.Statements))
+		}
+
+		stmt := program.Statements[0]
+		if !testAssignmentStatement(t, stmt, tt.expectedIdentifier) {
+			return
+		}
+
+		val := stmt.(*ast.AssignmentStatement).Value
+		if !testLiteralExpression(t, val, tt.expectedValue) {
+			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())
@@ -1066,3 +1100,29 @@ func checkParserErrors(t *testing.T, p *Parser) {
 	}
 	t.FailNow()
 }
+
+func testAssignmentStatement(t *testing.T, s ast.Statement, name string) bool {
+	if s.TokenLiteral() != "=" {
+		t.Errorf("s.TokenLiteral not '='. got=%q", s.TokenLiteral())
+		return false
+	}
+
+	assignStmt, ok := s.(*ast.AssignmentStatement)
+	if !ok {
+		t.Errorf("s not *ast.AssignmentStatement. got=%T", s)
+		return false
+	}
+
+	if assignStmt.Name.Value != name {
+		t.Errorf("assignStmt.Name.Value not '%s'. got=%s", name, assignStmt.Name.Value)
+		return false
+	}
+
+	if assignStmt.Name.TokenLiteral() != name {
+		t.Errorf("assignStmt.Name.TokenLiteral() not '%s'. got=%s",
+			name, assignStmt.Name.TokenLiteral())
+		return false
+	}
+
+	return true
+}