Change the Monkey parser to expect expression statements to either end in a semicolon, a closing brace (because of `if (x) { foo }`) or EOF

expend_end_statement.patch

diff --git a/parser/parser.go b/parser/parser.go
index dbd581d..c7ebdf9 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -114,6 +114,20 @@ func (p *Parser) expectPeek(t token.TokenType) bool {
 	}
 }
 
+func (p *Parser) expectStatementEnd() bool {
+	switch p.peekToken.Type {
+	case token.SEMICOLON, token.EOF:
+		p.nextToken()
+		return true
+	case token.RBRACE:
+		// do not consume it
+		return true
+	default:
+		p.peekError(token.SEMICOLON)
+		return false
+	}
+}
+
 func (p *Parser) Errors() []string {
 	return p.errors
 }
@@ -202,9 +216,7 @@ func (p *Parser) parseExpressionStatement() *ast.ExpressionStatement {
 
 	stmt.Expression = p.parseExpression(LOWEST)
 
-	if p.peekTokenIs(token.SEMICOLON) {
-		p.nextToken()
-	}
+	p.expectStatementEnd()
 
 	return stmt
 }
diff --git a/parser/parser_test.go b/parser/parser_test.go
index 75f08bf..6865628 100644
--- a/parser/parser_test.go
+++ b/parser/parser_test.go
@@ -656,6 +656,23 @@ func TestCallExpressionParsing(t *testing.T) {
 	testInfixExpression(t, exp.Arguments[2], 4, "+", 5)
 }
 
+func TestCallExpressionWithoutParens(t *testing.T) {
+	input := `puts "hello"`
+
+	l := lexer.New(input)
+	p := New(l)
+	_ = p.ParseProgram()
+
+	errs := p.Errors()
+	if len(errs) != 1 {
+		t.Errorf("expected parser errors, but got none")
+	}
+
+	if have, want := errs[0], "expected next token to be ;, got STRING instead"; have != want {
+		t.Errorf("wrong error. want=%q, have=%q", want, have)
+	}
+}
+
 func TestCallExpressionParameterParsing(t *testing.T) {
 	tests := []struct {
 		input         string