{ t52_strcat_nest: nested concatenations, a concatenation compared, and a
  string ELEMENT as an operand.

  `+' associates to the left, so `a + b + '!'' is two occurrences and gets two
  scratch strings, and the first result is still alive when the second consumes
  it.  A concatenation result is an ordinary string variable, so it can be an
  operand of `=' (ParseCmp), and `+' can take an `s[i]' element as its left
  operand, in which case an element ADDRESS is what reaches the runtime rather
  than a whole-string address.

  a[2] is 'e' - subscripts are 1-based, the length byte is at s[0]. }
program t52_strcat_nest (input, output);
var
   a, b : string[12];
begin
   a := 'hello';
   b := 'world';
   writeln (a + b + '!');          { (a + b) + '!' }
   writeln ('<' + a + '>');        { ('<' + a) + '>' }
   if (a + b) = 'helloworld' then
      writeln ('concat-eq')
   else
      writeln ('concat-ne');
   writeln (a[2] + b)              { a string element + a string }
end.