Re: x versus _ as x ????
"Walter Cazzola [email protected] [ocaml_beginners]" <[email protected]> Sun, 27 Nov 2016 21:21:02 +0100 (CET)
| Newsgroups | gmane.comp.lang.ocaml.beginners |
|---|---|
| Message-ID | <[email protected]> |
--5-PnFG7AowMBah5wbgn1mGs279hCoL-sJNgZemk Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Hi, I don't know what riffle does in mathematica but both these functions doesn't compile because a rec is missing from the add_two_lists definition. As per the "as" this just label the thing matched so x is associated to the first list whereas y is associated to the couple [], _ (where _ is a list) and this makes some troubles to the type systems that find a list of list of couples (in the second entry of the match) instead of a list of list as in the first entry of the match. I think your error is with the associativity of , and "as": , is evaluated before "as" I hope this helps Walter On Sun, 27 Nov 2016, Douglas Lewit [email protected] [ocaml_beginners] wrote: > Hi everyone, > > I created my own little riffle function. It's similar ( but not exactly > the same as ) Wolfram Mathematica's Riffle function. Mathematica's Riffle > output is limited by the length of the smaller list. My riffle output's > length is determined by the length of the larger list. A small difference > really. Anyhow, here is my function: > > let riffle list1 list2 = let add_two_lists l1 l2 l3 = > match l1, l2 with > |x, [ ] -> l3 @ x > |[ ], y -> l3 @ y > |h1 :: t1, h2 :: t2 -> h1 :: h2 :: > add_two_lists t1 t2 l3 in > add_two_lists list1 list2 [ ] ;; > > It works great! It works exactly as I want it to, BUT HERE'S THE PROBLEM. > The following function DOES NOT EVEN COMPILE!!!! Why???? > > *let riffle list1 list2 = let add_two_lists l1 l2 l3 = * > * match l1, l2 with * > * |_ as x, [ ] -> l3 @ x* > * |[ ], _ as y -> l3 @ y* > * |h1 :: t1, h2 :: t2 -> h1 :: h2 :: > add_two_lists t1 t2 l3 in * > * add_two_lists list1 list2 [ ] ;;* > > Perhaps I do not fully understand how to use the "as" keyword, but I > thought that the two functions should compile and produce the exact same > output. What's the difference between the two forms? I appreciate the > feedback! > > Best, > > Douglas Lewit. > > P.S. Can someone provide a simple example of how to initialize and use a > Map data structure? > -- --5-PnFG7AowMBah5wbgn1mGs279hCoL-sJNgZemk Content-Type: text/html; charset=US-ASCII 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>Hi,<br> I don't know what riffle does in mathematica but both these functions<br> doesn't compile because a rec is missing from the add_two_lists<br> definition.<br> <br> As per the "as" this just label the thing matched so x is associated to<br> the first list whereas y is associated to the couple [], _ (where _ is a<br> list) and this makes some troubles to the type systems that find a list<br> of list of couples (in the second entry of the match) instead of a list<br> of list as in the first entry of the match. I think your error is with<br> the associativity of , and "as": , is evaluated before "as"<br> <br> I hope this helps<br> <br> Walter<br> <br> On Sun, 27 Nov 2016, Douglas Lewit [email protected] [ocaml_beginners] wrote:<br> <br> > Hi everyone,<br> ><br> > I created my own little riffle function. It's similar ( but not exactly<br> > the same as ) Wolfram Mathematica's Riffle function. Mathematica's Riffle<br> > output is limited by the length of the smaller list. My riffle output's<br> > length is determined by the length of the larger list. A small difference<br> > really. Anyhow, here is my function:<br> ><br> > let riffle list1 list2 = let add_two_lists l1 l2 l3 =<br> > match l1, l2 with<br> > |x, [ ] -> l3 @ x<br> > |[ ], y -> l3 @ y<br> > |h1 :: t1, h2 :: t2 -> h1 :: h2 ::<br> > add_two_lists t1 t2 l3 in<br> > add_two_lists list1 list2 [ ] ;;<br> ><br> > It works great! It works exactly as I want it to, BUT HERE'S THE PROBLEM.<br> > The following function DOES NOT EVEN COMPILE!!!! Why????<br> ><br> > *let riffle list1 list2 = let add_two_lists l1 l2 l3 = *<br> > * match l1, l2 with *<br> > * |_ as x, [ ] -> l3 @ x*<br> > * |[ ], _ as y -> l3 @ y*<br> > * |h1 :: t1, h2 :: t2 -> h1 :: h2 ::<br> > add_two_lists t1 t2 l3 in *<br> > * add_two_lists list1 list2 [ ] ;;*<br> ><br> > Perhaps I do not fully understand how to use the "as" keyword, but I<br> > thought that the two functions should compile and produce the exact same<br> > output. What's the difference between the two forms? I appreciate the<br> > feedback!<br> ><br> > Best,<br> ><br> > Douglas Lewit.<br> ><br> > P.S. Can someone provide a simple example of how to initialize and use a<br> > Map data structure?<br> ><br> <br> -- <br> </p> </div> <!--~-|**|PrettyHtmlStart|**|-~--> <div style="color: #fff; height: 0;">__._,_.___</div> <div style="clear:both"> </div> <div id="fromDMARC" style="margin-top: 10px;"> <hr style="height:2px ; border-width:0; color:#E3E3E3; background-color:#E3E3E3;"> Posted by: Walter Cazzola <[email protected]> <hr style="height:2px ; border-width:0; color:#E3E3E3; background-color:#E3E3E3;"> </div> <div style="clear:both"> </div> <table cellspacing=4px style="margin-top: 10px; margin-bottom: 10px; color: #2D50FD;"> <tbody> <tr> <td style="font-size: 12px; font-family: arial; font-weight: bold; padding: 7px 5px 5px;" > <a style="text-decoration: none; color: #2D50FD" href="https://groups.yahoo.com/neo/groups/ocaml_beginners/conversations/messages/14724;_ylc=X3oDMTJxdm1wbzNjBF9TAzk3MzU5NzE0BGdycElkAzQ5OTkxOTQEZ3Jwc3BJZAMxNzA1MDA2NzY0BG1zZ0lkAzE0NzI0BHNlYwNmdHIEc2xrA3JwbHkEc3RpbWUDMTQ4MDI3ODA3Mg--?act=reply&messageNum=14724">Reply via web post</a> </td> <td>•</td> <td style="font-size: 12px; font-family: arial; padding: 7px 5px 5px;" > <a href="mailto:[email protected]?subject=Re%3A%20%22ocaml_beginners%22%3A%3A%5B%5D%20x%20versus%20_%20as%20x%20%3F%3F%3F%3F" style="text-decoration: none; color: #2D50FD;"> Reply to sender </a> </td> <td>•</td> <td style="font-size: 12px; font-family: arial; padding: 7px 5px 5px;"> <a href="mailto:[email protected]?subject=Re%3A%20%22ocaml_beginners%22%3A%3A%5B%5D%20x%20versus%20_%20as%20x%20%3F%3F%3F%3F" style="text-decoration: none; color: #2D50FD"> Reply to group </a> </td> <td>•</td> <td style="font-size: 12px; font-family: arial; padding: 7px 5px 5px;" > <a href="https://groups.yahoo.com/neo/groups/ocaml_beginners/conversations/newtopic;_ylc=X3oDMTJlbDJ2ajU4BF9TAzk3MzU5NzE0BGdycElkAzQ5OTkxOTQEZ3Jwc3BJZAMxNzA1MDA2NzY0BHNlYwNmdHIEc2xrA250cGMEc3RpbWUDMTQ4MDI3ODA3Mg--" style="text-decoration: none; color: #2D50FD">Start a New Topic</a> </td> <td>•</td> <td style="font-size: 12px; font-family: arial; padding: 7px 5px 5px;color: #2D50FD;" > <a href="https://groups.yahoo.com/neo/groups/ocaml_beginners/conversations/topics/14722;_ylc=X3oDMTM2OGQzbTcyBF9TAzk3MzU5NzE0BGdycElkAzQ5OTkxOTQEZ3Jwc3BJZAMxNzA1MDA2NzY0BG1zZ0lkAzE0NzI0BHNlYwNmdHIEc2xrA3Z0cGMEc3RpbWUDMTQ4MDI3ODA3MgR0cGNJZAMxNDcyMg--" style="text-decoration: none; color: #2D50FD;">Messages in this topic</a> (3) </td> </tr> </tbody> </table> <div id="megaphoneModule"> <hr style="height:2px ; border-width:0; color:#E3E3E3; background-color:#E3E3E3;"> <div> <div class="stream" style="margin-bottom:10px;"> <div style="background-color:white;"> <div class="sn-img" style="display:inline;"><img name="tn_file" style="padding:0px 10px;vertical-align:top;margin-top:5px;" src="https://s.yimg.com/ru/static/images/yg/img/megaphone/1464031581_phpFA8bON" height="82" width="82"></div> <div class="mod-txt" style="display:inline-block;"> <a rel="nofollow" name="sub_url" target="_blank" href="https://yho.com/1wwmgg" style="color:#0000FF;display:block;margin-left:5px;text-decoration:none;"><span style="font-size:15px;">Have you tried the highest rated email app?</span></a> <div style="max-width:530px;padding:2px 5px;">With 4.5 stars in iTunes, the Yahoo Mail app is the highest rated email app on the market. 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