Parrot in the Real World Dan Sugalski dan@sidhe.org April 29, 2019

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

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

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

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

DecisionPlus Language Basic Architecture DecisionPlus Language Reports Screens Engine Database Screen

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

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

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

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

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

SCO Unix as our platform Need anything more be said?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Questions ?