Title here
Summary here
Channel Directions in Pascal
program ChannelDirections;
uses
SysUtils;
type
TStringChannel = record
Value: string;
Filled: Boolean;
end;
procedure Ping(var pings: TStringChannel; msg: string);
begin
pings.Value := msg;
pings.Filled := True;
end;
procedure Pong(var pings, pongs: TStringChannel);
begin
if pings.Filled then
begin
pongs.Value := pings.Value;
pongs.Filled := True;
pings.Filled := False;
end;
end;
var
pings, pongs: TStringChannel;
begin
Ping(pings, 'passed message');
Pong(pings, pongs);
if pongs.Filled then
WriteLn(pongs.Value);
end.When using channels as function parameters in Pascal, we can specify if a channel is meant to only send or receive values. This specificity increases the type-safety of the program.
The Ping procedure only accepts a channel for sending values. It would be a compile-time error to try to receive on this channel.
procedure Ping(var pings: TStringChannel; msg: string);
begin
pings.Value := msg;
pings.Filled := True;
end;The Pong procedure accepts one channel for receives (pings) and a second for sends (pongs).
procedure Pong(var pings, pongs: TStringChannel);
begin
if pings.Filled then
begin
pongs.Value := pings.Value;
pongs.Filled := True;
pings.Filled := False;
end;
end;In the main program:
var
pings, pongs: TStringChannel;
begin
Ping(pings, 'passed message');
Pong(pings, pongs);
if pongs.Filled then
WriteLn(pongs.Value);
end.To run the program, save it as ChannelDirections.pas and compile it using a Pascal compiler:
$ fpc ChannelDirections.pas
$ ./ChannelDirections
passed messageNote that Pascal doesn’t have built-in support for channels like some modern languages. This example uses a simple record structure to simulate a channel-like behavior. In a real-world scenario, you might want to use more sophisticated concurrency primitives available in your Pascal implementation or external libraries.