Hi
Based on discussion about "for in" I want to suggest my proposition.
When we investigate some code, sometimes we found pattern:
Pattern 1:
/ begin
startfun;
try
...
finally
stopfun;
end;
/ end;
Pattern 2:
for i:= startfun to stopfun do begin
....
end;
Pattern 3:
startfun;
while stopfun do begin
...
end;
Common for all mentioned patterns are two connected functions, which
controlled running of body source. First make all initializations,
second helping with iterations and finalizations.
My proposition is make possibility of join, those pair to one
sentence. All patterns can be change to one common template:
if startfun then repeat
until stopfun;
I You see we need two function with boolean result. Of course
possibility of parameters give wide appliance.
To preserve pascalish style I propose something like this:
tMyObject = class(tObject)
function startfun:boolean;
function stopfun:boolean;
property lambdafun; start startfun stop stopfun;
end;
and invoke:
var
t : tMyObject;
begin
..
t.lambdafun do begin
....
end;
end;
because on declaration side is similar do properties (also two function)
we can use the same syntax. Only keyword start and stop exchange read
and write.
To using i thought about WITH, but it may confusing bit, thus I
propose omit, and only use keyword DO.
Why lambda. Because is very similar to constructing no name procedures
and use them as normal. We have few mechanism controlling runnig: IF,
REPEAT, WHILE, FOR. They work well, but sometimes they are week. For
example we don't have enough primitives do build own implementation
FORIN method, on iterators also. But in Lisp any mechanism, any sequence
of computing collection can be done and source is very readable
lisp syntax: (lambda (<formal parameters>) <body>)
This is not unusual, but we can send this declaration as argument of
procedure.
Of course syntax like this
tlist.foreach( procedure (x : tObject);begin writeln(x) end)
is ugly (thought I sow something similar in C++/boost)
but when we change it a bit:
tlist.foreach(x) do begin
writeln(x);
end;
its not so strange
Because my english is very poor I only show some application
EXP. mutex (and patterns as RIAA)
tMutex = class
property makeatomic; start lock stop unlock;
end;
.....
begin
tMutex.makeatomic do begin
...
end;
end;
EXP: foreach
tMyList = class
function tMyList.start:boolean;
begin
current:=first;
result:=current<>nil;
end;
function tMyList.stop:boolean;
begin
current:=next(current);
resutl:=current<>nil;
end;
When attributes are added, or exception caching this will be more flexible.
--
Darek
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