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From: kolc7797@PROBLEM_WITH_YOUR_MAIL_GATEWAY_FILE.nyu.edu (Fanni Kolchina)
Subject: Constraint Error - Please Help
Date: 1998/12/02
Message-ID: <7445iv$gog$1@news.nyu.edu>#1/1
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X-Trace: news.nyu.edu 912628127 17168 (None) 128.122.20.15
Organization: New York University
Newsgroups: comp.lang.ada
Date: 1998-12-02T00:00:00+00:00
List-Id: <comp.lang.ada>

Hi, All:

I am writing a generic sorting program in Ada using heap sort.  I am
new to Ada, and have no experience with this. When I run my program, I
get a Constraint Error: range error. I have spent lots of time
thinking what is wrong, but I just cannot comprehend it. 
If someone could help me, I will greatly appreciate it.  Below is my
code, and the line where the exception is thrown is marked by comment
lines above and below it.  Thanks a lot!

with ada.text_io;			use ada.text_io;
with ada.integer_text_io;           use ada.integer_text_io;
with ada.float_text_io;             use ada.float_text_io;

procedure test_sort is
   
   generic
      type ITEM is private;
      type SORT_ARRAY is array(Positive range <>) of ITEM;
      with function "<" (u,v: ITEM) return boolean is <>;
      
      function sort_generic (x: SORT_ARRAY) return SORT_ARRAY;
      
      subtype index is positive range 1..10;
      type floatArray is array (positive range <>) of float;
    fa, hfa, shfa: floatArray(index);
    
    procedure printFloatArray (fa: floatArray) is
    begin
       for count in fa'first..fa'last loop
         put(fa(count), fore=>3, aft=>1, exp =>0);
       end loop;
       new_line;
    end;
    
    function sort_generic (x: SORT_ARRAY) return SORT_ARRAY is
       copy: SORT_ARRAY(x'range);
       last, left, right, max_l_r, current, this, parent: integer;
       end_node, contents : ITEM;
    begin
       
    for i in x'first..x'last loop
       copy(i):=x(i);
    end loop;
    
    for i in x'first+1..x'last loop
       this:=i;
       parent:= (i-1)/2;
       contents:=copy(this);
----------------------------------------------------------------
-- here's the line with the exception ---
       while this /= x'first and then copy(parent)<contents loop
----------------------------------------------------------------
         copy(this):= copy(parent);
	   this:= parent;
	     parent:=(parent-1)/2;
       end loop;
       copy(this):=contents;
    end loop;
    
    for last in reverse x'first+1..x'last loop
       --swap first position with last
       --end_node needs to be filtered down into heap
       end_node:= copy(last);
       copy(last):=copy(x'first);
       
       --start at the root node
       current:=x'first;
       --traverse the heap
       loop
         --look left
	   left:=2*current+1;
	     --if no left node, you've found the right slot
	       exit when left>last-1;
	         -- if there is a left node then find whether left or 
		   -- right node (if any) is max_l_r
		     right:=left+1;
		       if right>last-1 or copy(right)<copy(left) then
		            max_l_r:= left;
			      else
			           max_l_r:= right;
				     end if;
				       -- if end_node is bigger than
       both left and right children, then it
         -- must go here, so stop traversing
	   exit when copy(max_l_r) < end_node;
	     -- otherwise, move down
	       copy(current):=copy(max_l_r);
	         current:=max_l_r;
       end loop;
       -- after the loop, current points to the insertion spot
       copy(current):= end_node;
    end loop;
    return copy;
end;

function sortFloat is new sort_generic (float, floatArray, "<");
      
begin
   fa:=(7.2, 8.4, 3.5, 0.3, -5.4, 9.9, -0.5, 8.0, 1.1, 3.8);
   new_line;
   put("Testing sort for float vectors");
   new_line;
   put("Before: ");
   new_line;
   printFloatArray (fa);
   
   shfa:=sortFloat(fa);
   put("After: ");
   new_line;
   printFloatArray(fa);
   new_line;
end;