Re: [stack] peg: a lazy, non-deterministic concatenative language
"dustin.deweese" <[email protected]> Wed, 25 Apr 2012 11:38:10 -0000
| Newsgroups | gmane.comp.lang.concatenative |
|---|---|
| Message-ID | <[email protected]> |
--95fzZxjZA20AEvqLMSyJwmnPCfWUpwraML6OYD1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable --- In [email protected], Joshua Shinavier <parcour@...> wrote: >=20 > That's an interesting property, but it's not true of Ripple, and lazy > evaluation is the reason it's not true. Suppose we split a Ripple progra= m > arbitrarily and evaluate the fragments, e.g. >=20 > 4 sqrt. 10 add. >=20 > to >=20 > 4 sqrt. >=20 > and >=20 > 10 add. >=20 > They're both valid programs, yet the right-hand-side program has no > solutions while the complete program has two solutions ([8] and [12], or > (8) and (12) in Ripple syntax). Any time the right-hand-side does have a > solution, e.g. if the program had been (4 sqrt. 10), which is already ful= ly > reduced, the left-hand-side will never be reduced in the complete program= , > so it doesn't matter what its solutions are. >=20 > If Ripple used an eager evaluation strategy instead, the "cartesian > composition" rule would more or less hold. >=20 Peg also uses lazy evaluation, but the pureness of the language means that: 1 2 + 3 7 4 - are all equivalent and indistinguishable, whether evaluated or not, because= observing them requires evaluation. Because expressions need to terminate first in order to use the Cartesian c= omposition rule, non-termination does not pose a problem either. Also, in Peg, an expression will not reduce, rather than yielding no soluti= ons, if an argument to a word is missing i.e. the expression is a partially= applied function. So, 10 + --> 10 + which is different from "ten" + --> no (no results) --95fzZxjZA20AEvqLMSyJwmnPCfWUpwraML6OYD1 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> </head> <body style="background-color: #fff;"> <span style="display:none"> </span> <!--~-|**|PrettyHtmlStartT|**|-~--> <div id="ygrp-mlmsg" style="position:relative;"> <div id="ygrp-msg" style="z-index: 1;"> <!--~-|**|PrettyHtmlEndT|**|-~--> <div id="ygrp-text" > <p><br> <br> --- In <a href="mailto:concatenative%40yahoogroups.com">[email protected]</a>, Joshua Shinavier <parcour@...> wrote:<br> <br> > <br> > That's an interesting property, but it's not true of Ripple, and lazy<br> > evaluation is the reason it's not true. Suppose we split a Ripple program<br> > arbitrarily and evaluate the fragments, e.g.<br> > <br> > 4 sqrt. 10 add.<br> > <br> > to<br> > <br> > 4 sqrt.<br> > <br> > and<br> > <br> > 10 add.<br> > <br> > They're both valid programs, yet the right-hand-side program has no<br> > solutions while the complete program has two solutions ([8] and [12], or<br> > (8) and (12) in Ripple syntax). Any time the right-hand-side does have a<br> > solution, e.g. if the program had been (4 sqrt. 10), which is already fully<br> > reduced, the left-hand-side will never be reduced in the complete program,<br> > so it doesn't matter what its solutions are.<br> > <br> > If Ripple used an eager evaluation strategy instead, the "cartesian<br> > composition" rule would more or less hold.<br> > <br> <br> Peg also uses lazy evaluation, but the pureness of the language means that:<br> <br> 1 2 +<br> 3<br> 7 4 -<br> <br> are all equivalent and indistinguishable, whether evaluated or not, because observing them requires evaluation.<br> <br> Because expressions need to terminate first in order to use the Cartesian composition rule, non-termination does not pose a problem either.<br> <br> Also, in Peg, an expression will not reduce, rather than yielding no solutions, if an argument to a word is missing i.e. the expression is a partially applied function. So,<br> <br> 10 + --> 10 +<br> <br> which is different from<br> <br> "ten" + --> no (no results)<br> <br> </p> </div> <!--~-|**|PrettyHtmlStart|**|-~--> <div style="color: #fff; height: 0;">__._,_.___</div> <div id="ygrp-actbar" style="clear: both; margin-bottom: 10px; white-space: nowrap; color: #666; padding-top: 15px;"> <div> <a href="mailto:[email protected]?subject=Re%3A%20%5Bstack%5D%20peg%3A%20a%20lazy%2C%20non-deterministic%20concatenative%20language" style="margin-right: 0; padding-right: 0;"> Reply to <span style="font-weight: 700;">sender</span></a> | <a href="mailto:[email protected]?subject=Re%3A%20%5Bstack%5D%20peg%3A%20a%20lazy%2C%20non-deterministic%20concatenative%20language"> Reply to <span style="font-weight: 700;">group</span></a> | <a href="http://groups.yahoo.com/group/concatenative/post;_ylc=X3oDMTJwMmxqbWd1BF9TAzk3MzU5NzE0BGdycElkAzE4MzkyNzQEZ3Jwc3BJZAMxNzA1MDA2NzY0BG1zZ0lkAzQ5MjgEc2VjA2Z0cgRzbGsDcnBseQRzdGltZQMxMzM1MzUzODk1?act=reply&messageNum=4928">Reply <span style="font-weight: 700;">via web post</span></a> | <a href="http://groups.yahoo.com/group/concatenative/post;_ylc=X3oDMTJlYWJzdHBwBF9TAzk3MzU5NzE0BGdycElkAzE4MzkyNzQEZ3Jwc3BJZAMxNzA1MDA2NzY0BHNlYwNmdHIEc2xrA250cGMEc3RpbWUDMTMzNTM1Mzg5NQ--" style="font-weight: 700;">Start a New Topic</a> </div> <a href="http://groups.yahoo.com/group/concatenative/message/4915;_ylc=X3oDMTM0NnJxOWpyBF9TAzk3MzU5NzE0BGdycElkAzE4MzkyNzQEZ3Jwc3BJZAMxNzA1MDA2NzY0BG1zZ0lkAzQ5MjgEc2VjA2Z0cgRzbGsDdnRwYwRzdGltZQMxMzM1MzUzODk1BHRwY0lkAzQ5MTU-">Messages in this topic</a> (<span style="font-weight: 700;">14</span>) </div> <!------- Start Nav Bar ------> <!-- |**|begin egp html banner|**| --> <div id="ygrp-vital" style="background-color: #e0ecee; font-family: Verdana; font-size: 10px; margin-bottom: 10px; padding: 10px;"> <span id="vithd" style="font-weight: bold; color: #333; text-transform: uppercase; ">Recent Activity:</span> <ul style="list-style-type: none; margin: 0; padding: 0; display: inline;"> <li style="border-right: 1px solid #000; font-weight: 700; display: inline; padding: 0 5px; margin-left: 0;"> <span class="cat"><a href="http://groups.yahoo.com/group/concatenative/members;_ylc=X3oDMTJmbWh2MWs0BF9TAzk3MzU5NzE0BGdycElkAzE4MzkyNzQEZ3Jwc3BJZAMxNzA1MDA2NzY0BHNlYwN2dGwEc2xrA3ZtYnJzBHN0aW1lAzEzMzUzNTM4OTU-?o=6" style="text-decoration: none;">New Members</a></span> <span class="ct" style="color: #ff7900;">1</span> </li> </ul> <div style="clear: both; padding-top: 2px; color: #1e66ae;"> <a href="http://groups.yahoo.com/group/concatenative;_ylc=X3oDMTJlNjdlajc3BF9TAzk3MzU5NzE0BGdycElkAzE4MzkyNzQEZ3Jwc3BJZAMxNzA1MDA2NzY0BHNlYwN2dGwEc2xrA3ZnaHAEc3RpbWUDMTMzNTM1Mzg5NQ--" style="text-decoration: none;">Visit Your Group</a> </div> </div> <div id="ft" style="font-family: Arial; font-size: 11px; margin-top: 5px; padding: 0 2px 0 0; clear: both;"> <a href="http://groups.yahoo.com/;_ylc=X3oDMTJkaDFjdTJpBF9TAzk3MzU5NzE0BGdycElkAzE4MzkyNzQEZ3Jwc3BJZAMxNzA1MDA2NzY0BHNlYwNmdHIEc2xrA2dmcARzdGltZQMxMzM1MzUzODk1" style="float: left;"><img src="http://l.yimg.com/a/i/us/yg/logo/us.gif" height="15" width="137" alt="Yahoo! Groups" style="border: 0;"/></a> <div style="color: #747575; float: right;">Switch to: <a href="mailto:[email protected]?subject=Change Delivery Format: Traditional" style="text-decoration: none;">Text-Only</a>, <a href="mailto:[email protected]?subject=Email Delivery: Digest" class="margin-rt" style="text-decoration: none;">Daily Digest</a> • <a href="mailto:[email protected]?subject=Unsubscribe" style="text-decoration: none;">Unsubscribe</a> • <a href="http://docs.yahoo.com/info/terms/" style="text-decoration: none;">Terms of Use</a></div> </div> <!-- |**|end egp html banner|**| --> </div> <!-- ygrp-msg --> <!-- Sponsor --> <!-- |**|begin egp html banner|**| --> <div id="ygrp-sponsor" style="width:160px; float:right; clear:none; margin:0 0 25px 0; background: #fff;"> <!-- Start Recommendations --> <div id="ygrp-reco"> </div> <!-- End Recommendations --> </div> <!-- |**|end egp html banner|**| --> <div style="clear:both; color: #FFF; font-size:1px;">.</div> </div> <img src="http://geo.yahoo.com/serv?s=97359714/grpId=1839274/grpspId=1705006764/msgId=4928/stime=1335353895/nc1=3848643/nc2=5758221/nc3=4507179" width="1" height="1"> <br> <div style="color: #fff; height: 0;">__,_._,___</div> <!--~-|**|PrettyHtmlEnd|**|-~--> </body> <!--~-|**|PrettyHtmlStart|**|-~--> <head> <style type="text/css"> <!-- #ygrp-mkp { border: 1px solid #d8d8d8; font-family: Arial; margin: 10px 0; padding: 0 10px; } #ygrp-mkp hr { border: 1px solid #d8d8d8; } #ygrp-mkp #hd { color: #628c2a; font-size: 85%; font-weight: 700; line-height: 122%; margin: 10px 0; } #ygrp-mkp #ads { margin-bottom: 10px; } #ygrp-mkp .ad { padding: 0 0; } #ygrp-mkp .ad p { margin: 0; } #ygrp-mkp .ad a { color: #0000ff; text-decoration: none; } #ygrp-sponsor #ygrp-lc { font-family: Arial; } #ygrp-sponsor #ygrp-lc #hd { margin: 10px 0px; font-weight: 700; font-size: 78%; line-height: 122%; } #ygrp-sponsor #ygrp-lc .ad { margin-bottom: 10px; padding: 0 0; } a { color: #1e66ae; } #actions { font-family: Verdana; font-size: 11px; padding: 10px 0; } #activity { background-color: #e0ecee; float: left; font-family: Verdana; font-size: 10px; padding: 10px; } #activity span { font-weight: 700; } #activity span:first-child { text-transform: uppercase; } #activity span a { color: #5085b6; text-decoration: none; } #activity span span { color: #ff7900; } #activity span .underline { text-decoration: underline; } .attach { clear: both; display: table; font-family: Arial; font-size: 12px; padding: 10px 0; width: 400px; } .attach div a { text-decoration: none; } .attach img { border: none; padding-right: 5px; } .attach label { display: block; margin-bottom: 5px; } .attach label a { text-decoration: none; } blockquote { margin: 0 0 0 4px; } .bold { font-family: Arial; font-size: 13px; font-weight: 700; } .bold a { text-decoration: none; } dd.last p a { font-family: Verdana; font-weight: 700; } dd.last p span { margin-right: 10px; font-family: Verdana; font-weight: 700; } dd.last p span.yshortcuts { margin-right: 0; } div.attach-table div div a { text-decoration: none; } div.attach-table { width: 400px; } div.file-title a, div.file-title a:active, div.file-title a:hover, div.file-title a:visited { text-decoration: none; } div.photo-title a, div.photo-title a:active, div.photo-title a:hover, div.photo-title a:visited { text-decoration: none; } div#ygrp-mlmsg #ygrp-msg p a span.yshortcuts { font-family: Verdana; font-size: 10px; font-weight: normal; } .green { color: #628c2a; } .MsoNormal { margin: 0 0 0 0; } o { font-size: 0; } #photos div { float: left; width: 72px; } #photos div div { border: 1px solid #666666; height: 62px; overflow: hidden; width: 62px; } #photos div label { color: #666666; font-size: 10px; overflow: hidden; text-align: center; white-space: nowrap; width: 64px; } #reco-category { font-size: 77%; } #reco-desc { font-size: 77%; } .replbq { margin: 4px; } #ygrp-actbar div a:first-child { /* border-right: 0px solid #000;*/ margin-right: 2px; padding-right: 5px; } #ygrp-mlmsg { font-size: 13px; font-family: Arial, helvetica,clean, sans-serif; *font-size: small; *font: x-small; } #ygrp-mlmsg table { font-size: inherit; font: 100%; } #ygrp-mlmsg select, input, textarea { font: 99% Arial, Helvetica, clean, sans-serif; } #ygrp-mlmsg pre, code { font:115% monospace; *font-size:100%; } #ygrp-mlmsg * { line-height: 1.22em; } #ygrp-mlmsg #logo { padding-bottom: 10px; } #ygrp-mlmsg a { color: #1E66AE; } #ygrp-msg p a { font-family: Verdana; } #ygrp-msg p#attach-count span { color: #1E66AE; font-weight: 700; } #ygrp-reco #reco-head { color: #ff7900; font-weight: 700; } #ygrp-reco { margin-bottom: 20px; padding: 0px; } #ygrp-sponsor #ov li a { font-size: 130%; text-decoration: none; } #ygrp-sponsor #ov li { font-size: 77%; list-style-type: square; padding: 6px 0; } #ygrp-sponsor #ov ul { margin: 0; padding: 0 0 0 8px; } #ygrp-text { font-family: Georgia; } #ygrp-text p { margin: 0 0 1em 0; } #ygrp-text tt { font-size: 120%; } #ygrp-vital ul li:last-child { border-right: none !important; } --> </style> </head> <!--~-|**|PrettyHtmlEnd|**|-~--> </html> <!-- end group email --> --95fzZxjZA20AEvqLMSyJwmnPCfWUpwraML6OYD1--