Path: csiph.com!xmission!news.snarked.org!border2.nntp.dca1.giganews.com!nntp.giganews.com!news.iecc.com!.POSTED.news.iecc.com!nerds-end
From: "Ev. Drikos" <drikosev@gmail.com>
Newsgroups: comp.compilers
Subject: Re: Languages with optional spaces
Date: Mon, 2 Mar 2020 20:04:56 +0200
Organization: Aioe.org NNTP Server
Lines: 43
Sender: news@iecc.com
Approved: comp.compilers@iecc.com
Message-ID: <20-03-006@comp.compilers>
References: <20-02-015@comp.compilers> <20-02-033@comp.compilers> <20-02-034@comp.compilers> <20-03-003@comp.compilers> <20-03-005@comp.compilers>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Injection-Info: gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970"; logging-data="30038"; mail-complaints-to="abuse@iecc.com"
Keywords: lex, syntax
Posted-Date: 02 Mar 2020 18:19:09 EST
X-submission-address: compilers@iecc.com
X-moderator-address: compilers-request@iecc.com
X-FAQ-and-archives: http://compilers.iecc.com
Content-Language: en-US
Xref: csiph.com comp.compilers:2477

On 02/03/2020 08:33, Christopher F Clark wrote:
> ...
>
> As far as I can tell (and I haven't thought seriously about BASIC for
> years), there are roughly two cases.
>
   Neither I have thought seriously about any BASIC Dialect so far. The
example grammar in my previous message took me less than half an hour.

> 1) We have already identified the lower bound in "lower bound TO upper
> bound".  This can happen if we saw a number, or maybe an identifier
> without the word "TO" in it (followed by a space?).  This will not be
> true, if we just saw an operator such as "+" as we will be expecting
> another identifier to continue the expression...

One is supposed to progressively add syntax as needed. I just found such
a case at www.gkc.org.uk/martin/software/UK101-tapes.zip:

5120 FOR J=K+1TON4:A(K,J)=A(K,J)/P:NEXT J:I=1

Here is a more complete rule that parses ie "512 FOR J=LOWER+1TOUPPER"

<lbound> ::=
            <lbound> <rel-op> <lbound> ~: <rel-op>
      |     <lbound> <add-op> <lbound>
      |     <lbound> <mult-op> <lbound>
      |     <add-op> <lbound> -: { <mult-op> }
      |     <number>
      |     <id-p>

IMHO, the most difficult problems come with statements like "NEXT i,j"
that imply a shared end statement of two FOR loops and BASIC doesn't
seem to be as easy as Fortran where this problem has a simple solution:
https://github.com/drikosev/Fortran/blob/master/OMP_Legacy_Parser.txt

> ...
> So, what would I do?  I would do it in 3 parts.  A lexer, a "fixer",
> and a parser...

So, the suggestion is a fixer between the parser and the lexer. Ok, I
appreciate your opinion.

Ev. Drikos