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From: "luser.droog" <luser.dr...@gmail.com>
Newsgroups: comp.lang.postscript
Subject: Re: How to do Algebraic Mode in PS like the HP does?
Date: Sun, 30 Sep 2012 00:57:23 -0500
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luser.droog wrote:

> David Combs wrote:
> 
>> In article <ef3f384c-2a6e-4850-8286-7d75b4b63179@googlegroups.com>,
>> luser- -droog  <mijo...@yahoo.com> wrote:
>>>
>>>
>>>I'd suggest you take them one-at-a-time and start posting "How to do XX
>>>in PS like the HP does?" threads. I'll contribute!
>>>
>>>For algebraic mode, we'll need a LL(1) or LR parser. I'll go get my
>>>Dragon book...
>>>
>>>-- droog
>> 
>> 
>> Yes, if it were c, you'd need the lr stuff, I guess.
>> 
>> But just parenthesized expressions and function calls,
>> isn't that basically dead simple?  Recursive descent
>> or the like.  And so unlike an lr scheme, with
>> recursive descent the parsing code is readable and
>> understandable.  (Once someone does the first and
>> follow sets -- sort of beyond me!)
>> 
>> David
> 
> Here's a first draft. Converts a string containing
> an infix expression involving "*_+-" to a string
> containing the postfix equivalent.
> 
> To actually produce PS output, we'll need to expand the
> payload in the /oper dict and pre-scan the string to
> count operators so the size of the output string can
> be calculated.
>
 
A little more searching led me to this:
http://devmaster.net/posts/2866/processing-arithmetic-expressions-with-the-shunting-yard-algorithm

Looks very promising.