Beefy Boxes and Bandwidth Generously Provided by pair Networks
Your skill will accomplish
what the force of many cannot
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??
( Moritz: Thanks. Thursday, I grabbed a copy of the book and moved to the latest rakudo release. I didn't find the .perl method yet; so I'll just salivate for a while more. I will look again at the book--that was helpful. )

This is going slow as I have little time (and lots of ignorance) but I will keep scratching away.

#!/home/rir/rakudo/parrot_install/bin/perl6 { grammar Calc { token TOP { <expression> } rule expression { <lhs> <op> <rhs> } token lhs { <numeric> } token rhs { <numeric> } token numeric { \d+[\.\d*]? } token op { '-' | '+' | '*' | '/' | 'x' } } class Calc::Actions { method TOP($/) { make $<expression>.ast } method expression($/) { make eval "$/<lhs> $/<op>.ast() $/<rhs +>" } method lhs($/) { make $/ } method rhs($/) { make $/ } method numeric($/) { make $/ } method op($/) { if ( $/ eq 'x') { make '*'; } else {make $/; } + } } my $m = Calc.parse( "8.8 x 5.0 - 2", :actions( Calc::Actions)); die "dying no match" unless $m; say "$m<expression> = $m.ast()"; }
Ok, I have retrenched. I grabbed Rakudo's/Pug's spectest and found some grammars that compile out of the box. The above is built up from t/spec/S05-grammarr/action-stubs.t . (Running spectest was less onerous than I expected.)

The above is meant to model a cheap calculator.

Questions:

  • Is the string eval reasonable here?
  • Can the expression rule be handled without the separate naming of the lhs and rhs? Is there a way to access each numeric in something like:
    rule expression { <numeric> <op> <numeric> }
  • The above can easily be extended by changing the rhs token line to
    token rhs { <numeric> | <expression> }
    But this destroys the calculator's left associativity and equal precedence. I suppose this could be addressed by changing the rule expression line to:
    rule expression { <lhs> ( <op> <rhs> )+ }
    but I'm getting lost here.

Be well,
rir


In reply to Re^2: P6: Beginning grammar by rir
in thread P6: Beginning grammar by rir

Title:
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!
  • 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?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others studying the Monastery: (6)
    As of 2015-07-29 21:35 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









      Results (269 votes), past polls