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Re: implementation languages, was Supporting multiple input syntaxes

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luser droog <mijoryx@yahoo.com.dmarc.email.dmarc.email> schrieb:

[PostScript]

> But the language itself I just really enjoy. It's my "Lego blocks"
> language. The RPN syntax removes all ambiguity about precedence and
> sequencing.

I recently had the doubtful pleasure of evaluating the formula

x = ((a-b)*c^2+(-d^2+e^2-a^2+b^2)*c+a^2*b+(f^2-e^2-b^2)*a
    +(-f^2+d^2)*b)/((-2*d+2*e)*c+(2*f-2*e)*a-2*b*(f-d))

in Postscript.  (Yes, really.  Don't ask.)

It was the first time in more than a decade that I wrote a
flex/bison grammar (mostly copied from the bison manual).  It was
faster and less error-prone than trying to do it directly.

The grammar actually generated fairly unidiomatic PostScript
because I made it give names to all the variables, so

a-b

became

a b sub

I'm sure a real PostScript aficionado would have done it all
on the stack :-)
[Turning infix into RPN is a pretty basic intro compiler course exercise.  Conceptually,
you make the parse tree and then do a postorder tree walk.  Or if you'rs using yacc or
bison, in the expression grammar you just print the operator or token in the code for each
rule because they are recognized in the right order, e.g.:

expr:   VARIABLE { printf(" %s ", $1): }
  | expr '+' expr ( printf(" add "); }
  | expr '-' expr ( printf(" sub "); }
  | '(' expr ')' { /* print nothing */ }

-John]

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Thread

Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-12 15:20 -0700
  Re: Supporting multiple input syntaxes Kaz Kylheku <793-849-0957@kylheku.com> - 2020-08-13 00:43 +0000
  Re: Supporting multiple input syntaxes Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2020-08-13 10:27 +0200
    Re: Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-13 21:36 -0700
    Re: Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-23 22:16 -0700
  Re: Supporting multiple input syntaxes minforth@arcor.de - 2020-08-13 14:15 -0700
    Re: Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-13 21:37 -0700
    RE: Supporting mulitple input syntaxes Christopher F Clark <christopher.f.clark@compiler-resources.com> - 2020-08-14 12:44 +0300
  Supporting multiple input syntaxes David Lovemore <davidlovemore@gmail.com> - 2020-08-15 06:42 -0700
    Re: Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-15 15:20 -0700
      Re: Supporting multiple input syntaxes David Lovemore <davidlovemore@gmail.com> - 2020-08-16 02:21 -0700
        Re: Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-20 14:45 -0700
          Re: Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-23 19:35 -0700
            Re: implementation languages, was Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-23 20:39 -0700
              Re: implementation languages, was Supporting multiple input syntaxes Thomas Koenig <tkoenig@netcologne.de> - 2020-08-24 17:01 +0000
                Re: implementation languages, was Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-28 10:56 -0700
              Re: stack languages, was Supporting multiple input syntaxes luser droog <mijoryx@yahoo.com.dmarc.email> - 2020-08-24 12:14 -0700
  Re: Supporting multiple input syntaxes gah4 <gah4@u.washington.edu> - 2020-08-23 14:26 -0700
  Re: Supporting multiple input syntaxes antispam@math.uni.wroc.pl - 2021-02-11 23:27 +0000
    Re: Supporting multiple input syntaxes Elijah Stone <elronnd@elronnd.net> - 2021-02-17 01:44 -0800
      Re: Supporting multiple input syntaxes antispam@math.uni.wroc.pl - 2021-02-23 23:28 +0000
        Re: Supporting multiple input syntaxes "ltc...@gmail.com" <ltcmelo@gmail.com> - 2021-03-14 21:08 -0400
  Re: Supporting multiple input syntaxes Rock Brentwood <rockbrentwood@gmail.com> - 2021-03-14 17:36 -0700

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