Beefy Boxes and Bandwidth Generously Provided by pair Networks
Pathologically Eclectic Rubbish Lister

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

In a series of three articles in The Perl Review, now available online, I laid this proof out much more carefully, in three different versions. The most bullet-proof version derives the result directly from Rice's Theorem.

You are right that the proof would not go through if the only way of establishing a prototype for a Perl function was via a function definition. As I said in Perl Review (4.3, p. 28):

I must show that I can use Turing-complete Perl code to determine the prototype of the dunno subroutine at compile time. A function definition won’t work.

Summarizing from that article, there are at least two ways that the prototype of a subroutine can be established using Turing-complete Perl code. One is with symbol table manipulation, for example:

BEGIN { *dunno = sub () { 3 } }
A second way is to put the function definition into a string which is eval'd in a BEGIN block. I believe clever monks will be able to think of others.

In reply to Re^2: Perl Cannot Be Parsed: A Formal Proof by Jeffrey Kegler
in thread Perl Cannot Be Parsed: A Formal Proof by Jeffrey Kegler

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 the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others chanting in the Monastery: (3)
    As of 2021-05-09 02:31 GMT
    Find Nodes?
      Voting Booth?
      Perl 7 will be out ...

      Results (100 votes). Check out past polls.