Can someone please explain in simple terms, why when I do

 r:=foo(r), where "r" is a Record, then the returned  "r" is not what is returned from foo()?  I want to write a proc foo() which takes in a Record variable, update some of its fields, and then return the updated Record to the caller

r:=Record('a','b');
foo:=proc(r)
    r:-b:=5;
    return(r);
end proc;

But now when I call the above as follows

r:-b:=99;
print(r);
r:=foo(r):
print(r);

The last print above just prints "r" and not the Record. It seems to have erased the Record.

But it works, if I change the name of the variable to return the result into, as 

r:-b:=99;
print(r);
r0:=foo(r):
print(r0);

When I do the same on say a Matrix, there is no problem

restart;
r:=<<1,1>>:
foo:=proc(r)
    r[1]:=5;
    return(r);
end proc;

And now

r;
r:=foo(r):
print(r);

Why it worked with a Matrix but not with Record? Why can't one overwrite the Record on the call return?

What would be the correct way to pass in a Record to a function, and have the function update some of its fields, and then return back the updated copy of the Record without having to make a new variable "r0" as above?

I really like Maple Record. I think it is one of the hidden gems in Maple. Very useful.

But I have basic questions on it. I just started to learn how to use it. It is very similar to Pascal Record.

1)

r:=Record(a,b);
                       r := Record(a, b)
type(r,'record');
                              true
whattype(r);
                             symbol

Why  type(r,'record') says true, but whattype(r) says symbol?

2)
Why Maple displays the record content to the screen automatically only first time, after it is created, but second time, it only echos the name? So one has to use print() each time to display the content of the record.  Not a big deal, but it is little annoying

r:=Record(a,b);
                       r := Record(a, b)
r;
                               r

print(r);
                          Record(a, b)

r:-a:=5;
                             a := 5
r
                               r

print(r);
                        Record(a = 5, b)

Compare this to say a set type, where it displays the content each time

r:={1,2,3};
                         r := {1, 2, 3}
r
                           {1, 2, 3}

I tried changing max_record_depth but I must be doing something wrong. It still does not display the content

interface(max_record_depth=10)
                               10
r:=Record(a,b);
                       r := Record(a, b)
r;
                               r

3) Why are these two behave the same way

r:=Record("y");
r:-y:=4;

r:=Record('y');
r:-y:=4;

Giving the name of the field as string worked the same way as second example which is a name.  I thought the first one above will not work as field name should be a name according to help.

One of the frustrating things I am finding in using Maple debugger is that I can't set breakpoint using stopat() at some line number in some inner module, if the inner module is local module. It has to be an exported module.

Here is an example

restart;
foo:=module()
   export main_entry;
   local foo1; #inner module. But if local, Can't set breakpoint from outside

   foo1:=module()
     export main_entry;
     local foo2;

     foo2:=proc() #or breakpoint in first line here
        local s,x;
        s:=1;     #suppose I want to set break point here
        s:=s+sin(x);
     end proc;
     
     main_entry:=proc()         
        foo2();
     end proc;    
  end module;

  main_entry :=proc()
    foo1:-main_entry(); #call inner module's proc
  end proc;

end module;

Since there is inner module, local to outside module, I can't set break into the inner module procs anywhere.

stopat(foo:-foo1::foo2);
Error, module does not export `foo1`

A workaround for now is to change "local" to "export" on the inner modules declarations I want to debug, so I can setbreak points inside them, then when done, make them local again. So changed "local foo1" to "export foo1" above, and now

          stopat(foo:-foo1::foo2,2);

works.

This was also a little strange to me, since foo2() is a LOCAL proc to module foo1, yet Maple did not complain like it did when module foo1 was a LOCAL module to foo. I would have expected Maple to complain again for same reason.

So I am using the above workaround for now. But it is just a little annoying becuase I have to keep changing module from LOCAL to EXPORT in order to set breakpoints, then remember to make them local again.

Is there a better workaround?

A product suggestion: make stopat() ignore the local module setting and treat it as export for the purpose of setting a break point. This way one does not have to change the code just to set a breakpoint. Or if not to change current behavior, add a new option, as in

          stopat(........, option= ignore_local_setting)

So the default remain the same as now, but with the new option, it will set breakpoint anywhere, even in local modules.

Thank you

From help it says

"For any variable used within a procedure without being explicitly
mentioned in a local localSequence; or global globalSequence; the
following rules are used to determine whether it is local or global:

The variable is searched for amongst the locals and globals (explicit or implicit)
in surrounding procedures, starting with the innermost.  If the name is
encountered as a parameter, local variable, or global variable of such
a surrounding procedure, that is what it refers to."

--------------------------------------------

So it seems if I do not use explicit "global" on a variable, Maple can figure
if it is global or not using the above rules. But when I use explicit "global"
on a variable, Maple did not seem to do the same thing. Here is an example
 

restart;
foo:=proc()
  local a, inner_proc;

  inner_proc := proc()
     local b;
     b   := ithprime(10);
     a   := b; #this assiged the global (to this proc)
               #variable, which is "a" correctly
  end proc;

  inner_proc();

  return(a);
end proc;

calling foo() gives 29.

But since the variable "a" in foo() is a global with respect to the inner_proc() (based on what the above help page seems to say), then why this does not work

restart;
foo:=proc()
  local a, inner_proc;

  inner_proc := proc()
     local b;
     global a;
     b   := ithprime(10);
     a   := b;                
  end proc;

  inner_proc();

  return(a);
end proc;

Now foo() returns "a". So Maple did not assign 29 to the global "a", (global to the inner_proc).

This for me makes little sense. Is global in Maple means the outermost scope only, skipping everything in between?

I thought global means any variable outside the proc itself. So if the proc() was inside another proc(), then the variables in the outer proc are global to the inner proc, even if they are declared local to the outer proc.

Why did Maple not do the assignment when I explicitly declare "a" to be global in the inner proc?

Why does Maple dsolve give this strange error from dsolve? I do not see that the input is wrong

restart;
F := x * ( y(x) + x*sqrt(x*y(x)) + sqrt(x^3*y(x)) );
ode:= diff(y(x),x) = F;
dsolve(ode,y(x));

I do not see where the input is invalid. I stared at it for 5 minutes.

Mathematica can solve this as follows

ode = y'[x] == x ( y[x] + x Sqrt[x y[x]] + Sqrt[x^3 y[x]]  )
DSolve[ode, y[x], x]

Did I type something wrong in Maple?

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