1. Parrot in the Real World
Dan Sugalski
April 29, 2019

2. A Presentation in two parts
Part 1 - The practical project
Part 2 - The ramifications

3. Yarde Metals Metals wholesaling company $200M+ year 400K+ items/year
400+ employees
6 branches

4. Metaltraq Whole company run on a package called Metaltraq
Handles sales, shipping, tracking, invoicing--pretty much everything
We have the source, all 460K lines of it
Unfortunately it’s in DecisionPlus

5. System Setup Whole company runs on a single server
All terminal-based access
ISAM database, one index per data file
Only access to data through DecisionPlus

6. DecisionPlus Language
Basic Architecture
DecisionPlus Language
Reports
Screens
Engine
Database
Screen

7. The Problems The underlying database engine has size issues
Integrated database is all ISAM
DecisonPlus, as a language, is nasty
Stuck on SCO Unix as a platform

8. The size issues Each data file has a maximum size limit
Our most active only holds about 17 months of data
That was 18 months a while back
Good for the company, bad for MIS

9. ISAM. Ick The only access to the data is via DecisionPlus
One index per table
Serious performance issues if you don’t use that index
Any data queries need MIS help

10. DecisionPlus Antique 4GL
Slightly more primitive than Parrot’s assembly language
No subroutines, just labels, goto, and gosub
No blocks, just continued lines
Limits on the length of a single line
No lexicals. Or, really, globals
Phenomenally primitive array access

11. Two language versions Forms, with screen interface
Reports, with looping, totalling, and cross-reference file support
Two versions of the same language, subtly different

12. SCO Unix as our platform
Need anything more be said?

13. The Original Plan Move database to Postgres
Compile all programs into Perl
Dump original source
Do all new work in Perl

14. So, of course it was doomed to failure
It was a good plan…
So, of course it was doomed to failure
Sort of

15. Transition to Postgres worked
We play trigger games to simulate ISAM behaviour
Auto-generate the “ISAM key”
DB thunking layer knows how to use this info
Nightly transfer gives us an up-to-date data warehouse
Already in production use

16. Destination: Perl… not so good
DecisionPlus is really primitive
No subroutines or functions, just labels you can goto and gosub to
No lexical variables either
Or, technically, any variables at all
The generated perl was horrible

17. Perl really isn’t a target language
Working around the scoping issues was… interesting
The resulting code looked like machine-generated code and wasn’t really editable
It was so non-perl that working with it would’ve really hurt
Performance penalties with no win

18. The New Plan Target Parrot instead We had the parser
We had a working compiler
Parrot was working fine

19. Balancing the Issues Parrot gave us multi-language capabilities
Most of which were theoretical
Engine was fast
But… untested
So we did the sensible thing--a test run

20. The Test Get a simple screen running Jan 9th deadline
Made it with hours to spare

21. Pretty big test Working DB access library
Working screen access library
70% of the language

22. What we have
6K lines of PIR code in support libraries and class libraries
~660 line DecisionPlus Parse::RecDescent grammar
5K line compiler in perl
Full interface to Postgres & ncurses
No C code at all

23. Project Status Currently in-house beta August general beta
Looking for a September or October rollout
Still got some things to thump, but they’re almost all compiler and runtime things
One big parrot bug

24. What this did for Parrot
Didn’t alter the design, though it did change the timetable some
Multimethod dispatch
Objects
Dynamic bytecode loading
Stress-tested Parrot a lot

25. The Ramifications Really nice target for many languages
Generating code is really, really easy
Interfacing’s simple
Dynaloading’s handy

26. Nice target Parrot maps well to procedural languages
Object and MMD systems makes custom data types simple
Surprisingly stable

27. Easy code generation AST->PIR translation is trivial
Parrot hides a lot of the tricky stuff
Calling Conventions
Register coloring
Instruction set maps nicely to most languages

28. C interfacing’s dead-easy
No C code needed
All with Parrot’s NCI interface
For a 2 hour hack it’s stood up really well

29. Dynamic loading games work
Parrot’s built-in compilation system’s easy to use
Loading bytecode, assembly, or PIR work the same way
Bit limited with compilers right now, alas

30. End conclusions Compilers really aren’t tough
Parrot’s a nice target for compilers
Our cross-language features do work as we’d hoped
Moving a 4GL to Parrot is reasonably (potentially easily) doable

31. Questions ?