Re: How to handle qualified identifiers such as x.y in a Pascal-like language

On Monday, June 20, 2011 03:43:24 pm John wrote:
>> Is this a reasonable way to approach the problem?
> [Pretty much. The standard way to handle references to an enclosing
> scope is with a display, the calling procedure passes the enclosing
> stack frame addresses as hidden parameters. If your language doesn't
> allow variable sized declarations or recursion, P.x will be at a fixed
> distance below the current stack frame so you can address it directly,
> but in a more general case, you need the display. See any 1970s
> compiler text for details. -John]


My language does allow recursion, so my approach won't work as
written. So the AST node for an Ident should have a field for
enclosing scope levels, not stack levels?


I looked at Aho's description of displays. Currently, my interpreter
is using a more abstract stack. It's a stack of pointers, so the first
declared variable in a scope goes at frame offset 0, the second at
offset 1, etc. I was thinking of dedicating offset 0 to be a pointer
to all the bookkeeping info, such as enclosing scope pointers. Will
this work as my language matures, or are there some glaring gotchas?
[You more or less need a static place to pick up a pointer to the
stack frame for the current invocation of each lexically enclosing
routine. I don't see any reason that pointer to the display in a fixed
place wouldn't work. It's covered in detail in any compiler text
written when people still worried about compiling Pascal. -John]

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