🚀 go-pugleaf

In article <594@tuck.nott-cs.UUCP> anw@maths.nott.ac.uk (Dr A. N. Walker) writes:
>[Clay Phipps (>>) and Steven Ryan (>) are surprised that:
>	>>	  begin int I := 0, K := 1;
>	>>	  ref int Ptr := I;
>	>>	  Ptr := K;
>	>>	  Print (I);
>	>>	  end
>prints 0 rather than 1.]

Various people have been trying to explain this one. Personally, I would write
it as follows.

	  begin
 	  loc int I := 0, K := 1;
	  loc ref int Ptr := I;
	  Ptr := K;
	  Print (I);
	  end

The keyword 'loc' (which is legal ALGOL 68) serves to introduce a local
variable-declaration (as opposed to the identity- (or constant-) declaration
which is written
	int Zero = 0, One = 1;  ).
You may regard 'loc' as a fancy way of writing 'ref', but with the added side
effect that it actually obtains some local space to be 'ref'ed at. So you see
at once that the mode (i.e. type) of I is 'ref int', and that Ptr is a
variable to hold pointers to 'ref int' variables such as I or K, rather than
their contents. Then there should be no surprises.

The reason the keyword 'loc' is optional is that it was added at the last
moment, the original idea having been to copy the exact syntax of the ALGOL 60
variable-declaration. Personally, I always put it in, and if you leave it out
my compiler annoys you with a Warning message.