Re: [stack] peg: a lazy, non-deterministic concatenative language
"dustin.deweese" <[email protected]> Thu, 19 Apr 2012 08:53:39 -0000
| Newsgroups | gmane.comp.lang.concatenative |
|---|---|
| Message-ID | <[email protected]> |
--uT7pBgieDVA3VixnJlnxZgxepkEr7v0azYKkN56 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable --- In [email protected], "William Tanksley, Jr" <wtanksleyjr@.= ..> wrote: > > Don Groves <dgpdx@...> wrote: > > Of course, any concatentative language doesn't have to use a stack, > > it's just most convenient. >=20 > "Convenient" is kind of vague. A stack is the only parameter-passing > data structure we know of that's computationally complete/Turing > equivalent and doesn't require application. You can also make a > concatenative language using a single integer accumulator, for > example, and it's simple to implement and understand (but it's > ridiculously weak). Since a stack is the only one we know about it's > of course the most convenient one we know about... But what ones don't > we know about? The stack works essentially as a sort of caching structure. Whichever cach= ing strategy you choose determines the data structure. Last in, first out =3D queue Highest/lowest weighted out =3D priority queue First in, first out =3D stack There can be only one =3D a single item (accumulator) I can't think of any other strategies that have a single unambiguous "top" = element. FIFO seems to be the only reasonable caching strategy, though. >=20 > Here's another question: is peg _formally_ concatenative? That is, > given two valid programs, is their concatenation also a valid program? > Are the semantics of the resulting program the composition of the > semantics of the original two? >=20 > I think the answer is "no". A program "a1" and "a2", both of which > deterministically execute something like "False assert" or an > undefined word (which means that they always halt). The concatenation > "a1 a2" will perform (deterministically) the semantics of a2, but > never a1. >=20 Peg is a pure functional language, so it doesn't matter if a1 is executed i= f a2 yields no results; the execution of a1 has no observable effects. The= exception is if a1 performs I/O. Unfortunately, I can't see any way to fi= x this, because the Peg interpreter could never perform any I/O for fear of= an unseen 'False assert' being concatenated to the right. For Peg, it is formally concatenative with some modifications: 1. The expression to the right must be fully evaluated before evaluation of= a sub-expression containing an IO token. 2. Concatenation must be performed on the Cartesian products of the results= of evaluation of the sub-expressions --uT7pBgieDVA3VixnJlnxZgxepkEr7v0azYKkN56 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>, "William Tanksley, Jr" <wtanksleyjr@...> wrote:<br> ><br> > Don Groves <dgpdx@...> wrote:<br> > > Of course, any concatentative language doesn't have to use a stack,<br> > > it's just most convenient.<br> > <br> > "Convenient" is kind of vague. A stack is the only parameter-passing<br> > data structure we know of that's computationally complete/Turing<br> > equivalent and doesn't require application. You can also make a<br> > concatenative language using a single integer accumulator, for<br> > example, and it's simple to implement and understand (but it's<br> > ridiculously weak). Since a stack is the only one we know about it's<br> > of course the most convenient one we know about... But what ones don't<br> > we know about?<br> <br> The stack works essentially as a sort of caching structure. Whichever caching strategy you choose determines the data structure.<br> <br> Last in, first out = queue<br> Highest/lowest weighted out = priority queue<br> First in, first out = stack<br> There can be only one = a single item (accumulator)<br> <br> I can't think of any other strategies that have a single unambiguous "top" element. FIFO seems to be the only reasonable caching strategy, though.<br> <br> > <br> > Here's another question: is peg _formally_ concatenative? That is,<br> > given two valid programs, is their concatenation also a valid program?<br> > Are the semantics of the resulting program the composition of the<br> > semantics of the original two?<br> > <br> > I think the answer is "no". A program "a1" and "a2", both of which<br> > deterministically execute something like "False assert" or an<br> > undefined word (which means that they always halt). The concatenation<br> > "a1 a2" will perform (deterministically) the semantics of a2, but<br> > never a1.<br> > <br> <br> Peg is a pure functional language, so it doesn't matter if a1 is executed if a2 yields no results; the execution of a1 has no observable effects. The exception is if a1 performs I/O. Unfortunately, I can't see any way to fix this, because the Peg interpreter could never perform any I/O for fear of an unseen 'False assert' being concatenated to the right.<br> <br> For Peg, it is formally concatenative with some modifications:<br> <br> 1. The expression to the right must be fully evaluated before evaluation of a sub-expression containing an IO token.<br> 2. Concatenation must be performed on the Cartesian products of the results of evaluation of the sub-expressions<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=X3oDMTJwbzZhNXM0BF9TAzk3MzU5NzE0BGdycElkAzE4MzkyNzQEZ3Jwc3BJZAMxNzA1MDA2NzY0BG1zZ0lkAzQ5MjIEc2VjA2Z0cgRzbGsDcnBseQRzdGltZQMxMzM0ODI1NjIz?act=reply&messageNum=4922">Reply <span style="font-weight: 700;">via web post</span></a> | <a href="http://groups.yahoo.com/group/concatenative/post;_ylc=X3oDMTJlaWtvM3FxBF9TAzk3MzU5NzE0BGdycElkAzE4MzkyNzQEZ3Jwc3BJZAMxNzA1MDA2NzY0BHNlYwNmdHIEc2xrA250cGMEc3RpbWUDMTMzNDgyNTYyMw--" style="font-weight: 700;">Start a New Topic</a> </div> <a href="http://groups.yahoo.com/group/concatenative/message/4915;_ylc=X3oDMTM0dnI2ZjRtBF9TAzk3MzU5NzE0BGdycElkAzE4MzkyNzQEZ3Jwc3BJZAMxNzA1MDA2NzY0BG1zZ0lkAzQ5MjIEc2VjA2Z0cgRzbGsDdnRwYwRzdGltZQMxMzM0ODI1NjIzBHRwY0lkAzQ5MTU-">Messages in this topic</a> (<span style="font-weight: 700;">8</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=X3oDMTJmbzhhbWlsBF9TAzk3MzU5NzE0BGdycElkAzE4MzkyNzQEZ3Jwc3BJZAMxNzA1MDA2NzY0BHNlYwN2dGwEc2xrA3ZtYnJzBHN0aW1lAzEzMzQ4MjU2MjM-?o=6" style="text-decoration: none;">New Members</a></span> <span class="ct" style="color: #ff7900;">3</span> </li> </ul> <div style="clear: both; padding-top: 2px; color: #1e66ae;"> <a href="http://groups.yahoo.com/group/concatenative;_ylc=X3oDMTJldmpobXF2BF9TAzk3MzU5NzE0BGdycElkAzE4MzkyNzQEZ3Jwc3BJZAMxNzA1MDA2NzY0BHNlYwN2dGwEc2xrA3ZnaHAEc3RpbWUDMTMzNDgyNTYyMw--" 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=X3oDMTJkNXU0MXVjBF9TAzk3MzU5NzE0BGdycElkAzE4MzkyNzQEZ3Jwc3BJZAMxNzA1MDA2NzY0BHNlYwNmdHIEc2xrA2dmcARzdGltZQMxMzM0ODI1NjIz" style="float: left;"><img src="http://l.yimg.com/a/i/us/yg/logo/us.gif" height="15" width="137" alt="Yahoo! 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