What is the relationship between Functional Programming and Arpy? Is there one?
Find out at the next Melbourne meeting when Glen Kleidon (@Glen_Kleidon2) give an update on his Arpy project and a talk on Functional Programming.
Arpy is a framework that provides a new approach to web server development in Delphi. Glen first introduced us to his concept and initial development at our 2019 Symposium.
Functional programming in Delphi gives us ways to reduce lines of code and make the code more readable. Many newer languages are built with functional programming in mind. See how we can restructure code to use the new paradigm.
Come along and hear what Glen has to say, and chat with other members.
When: 6:00pm for a 6:15pm start
Where: At the Melbourne Men’s Shed, and on Zoom.
Zoom link will be up here shortly before the meeting starts.
Looking forward to it. It would be great if it was / could be also recorded, and released on our ADUG YouTube channel or other location, sometime down the track.
Topic: ADUG November 2022 Melbourne Meeting
Time: Nov 21, 2022 06:00 PM Canberra, Melbourne, Sydney
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Glen Kleidon gave quite an interesting presentation, there was a bit
on Arpy, and a bit related to functional programming.
Arpy has stalled somewhat.
Arpy is an implementation of web server-side architecture.
The architecture is similar to Node/Express. It seems likely good.
Embarcadero showed some initial interest in the product, but has
since not.
It has an architecture that allows the low-level http(s) drivers and
lots of the other handlers to be swapped in and out. They just need
the required interface(s) to be implemented.
The current builds are broken as the licensing has expired.
There was a suggestion that it may become open source
Functional Programming
This part of the presentation showed some of the difficulties
you run into when programming multi-threaded code using the OOP
paradigm. Where multiple threads can potentially alter state,
unless appropriate mechanisms are used to prevent this.
I found the demo using “the parallel for task” a bit interesting as the
task was broken up into the required number of tasks, but only ran
to the number of CPUs at a time.
Ten tasks, but running 2 at a time from start to completion, as
there were 2 CPUs.
Apparently functional programming helps with this.
(No Mutable state)
The effect you are observing is due to anonymous method variable capture mechanism. It does not capture variable values at specific point during code execution, but location of the variables.
Since all tasks run after the loop where you create them, you will see only the last value stored.
To solve your problem you have to add additional function ensuring that you don’t capture common variables in your task.
function CreateTask(vfirst, vlast, vsize, indtask: integer; var varray: Vet): ITask;
var
va: Vet;
begin
// var parameter cannot be captured so we have to store it into
// local variable - dynamic arrays act like pointers and any changes
// to local variable will actually change the original too
va := varray;
Result := TTask.Create(
procedure
begin
ProcA(vfirst, vlast, vsize, indtask, va);
end);
end;
And then you call it like
Ptasks[indtask] := CreateTask(vfirst, vlast, vsize, indtask, varray);
