Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!feeder.news-service.com!feeder3.cambriumusenet.nl!feed.tweaknews.nl!209.197.12.246.MISMATCH!nx02.iad01.newshosting.com!newshosting.com!news-out.readnews.com!news-xxxfer.readnews.com!news.misty.com!news.iecc.com!nerds-end From: noitalmost Newsgroups: comp.compilers Subject: Re: How to handle qualified identifiers such as x.y in a Pascal-like language Date: Thu, 23 Jun 2011 12:43:27 -0400 Organization: Compilers Central Lines: 26 Sender: news@iecc.com Approved: comp.compilers@iecc.com Message-ID: <11-06-042@comp.compilers> References: <11-06-037@comp.compilers> NNTP-Posting-Host: news.iecc.com X-Trace: gal.iecc.com 1308875775 68426 64.57.183.58 (24 Jun 2011 00:36:15 GMT) X-Complaints-To: abuse@iecc.com NNTP-Posting-Date: Fri, 24 Jun 2011 00:36:15 +0000 (UTC) Keywords: storage, code Posted-Date: 23 Jun 2011 20:36:15 EDT X-submission-address: compilers@iecc.com X-moderator-address: compilers-request@iecc.com X-FAQ-and-archives: http://compilers.iecc.com Xref: x330-a1.tempe.blueboxinc.net comp.compilers:168 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]