Beefy Boxes and Bandwidth Generously Provided by pair Networks
Welcome to the Monastery

Comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
(background aside for other's listening, AM's deserve no replies)

First let me clarify a few things. Firstly, within the BASIC interpreter itself, there's no formal "grammar" at all. Lines are dissected to find the statement being executed (the first token following the line number) and each statement's execution block has hard-wired into it a series of possible templates for that statement.

As one rude monk asked, "The art of language design hasn't been around for 25+ years without having come up with solutions to this kind of thing (...) did you do any research into language design before embarking on this project?" As a matter of fact I did. 25 years ago when I first saw this language, and shortly thereafer obtained assembler source code for implementations of the language, I learned how it was done. When I thought to recreate it for the Parrot CPU this is how it happened. The total number of assembly instructions is about 2k (for interactive mode, runtime, parser, everything).

When I get around to porting a pig like QuickBasic, I'll think about using a more open design with a formal grammar.

So discounting comments directed towards the interpreter itself, I'm left with the GW-BASIC to Parrot BASIC Perl script. This is (so far, and can remain) a simple filter. I don't want to teach it BASIC. The only statement's that's "special" is IF..THEN..ELSE. If the parser gets confused, it gets confused. This is what GW-BASIC was like.

(specifically to jepri)

Looking at talexb's solution and your description, I think I'm going to write a small state machine to process tokens on an IF..THEN line and arrange them accordingly. kvale's notes triggered a few light-bulbs as well. I'll post something shortly...

In reply to Re: Re: Clunky parsing problem, looking for simple solution by clintp
in thread Clunky parsing problem, looking for simple solution by clintp

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and all is quiet...

    How do I use this? | Other CB clients
    Other Users?
    Others browsing the Monastery: (6)
    As of 2018-01-22 01:32 GMT
    Find Nodes?
      Voting Booth?
      How did you see in the new year?

      Results (230 votes). Check out past polls.