Re: x versus _ as x ????
"Gabriel Scherer [email protected] [ocaml_beginners]" <[email protected]> Sun, 27 Nov 2016 15:17:47 -0500
| Newsgroups | gmane.comp.lang.ocaml.beginners |
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| Message-ID | <CAPFanBEB6MhLFXgN1_bHa+jv=8CbM_iZoL0cjHQjL5b-BGz3Tw@mail.gmail.com> |
--001a1143e56ae2c07105424e0ebc Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable The precedence of "as" is not intuitive, [], _ as y is parsed as ([], _) as y instead of, as you expected [], (_ as y) so the second line has a type error (y has the wrong type). I recommend parenthesizing explicitly when using "as". On Sun, Nov 27, 2016 at 3:06 PM, Douglas Lewit [email protected] [ocaml_beginners] <[email protected]> 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 Riffl= e > 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 differenc= e > really. Anyhow, here is my function: > > let riffle list1 list2 =3D let add_two_lists l1 l2 l3 =3D > 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 =3D let add_two_lists l1 l2 l3 =3D * > * 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? > > > >=20 > --001a1143e56ae2c07105424e0ebc Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/htm= l4/strict.dtd"> <html> <head> </head> =20 <body style=3D"background-color: #fff;"> <span style=3D"display:none"> </span> <!--~-|**|PrettyHtmlStartT|**|-~--> <div id=3D"ygrp-mlmsg" style=3D"position:relative;"> <div id=3D"ygrp-msg" style=3D"z-index: 1;"> <!--~-|**|PrettyHtmlEndT|**|-~--> <div id=3D"ygrp-text" > =20=20=20=20=20=20 =20=20=20=20=20=20 <p><div dir=3D"ltr"><div><div><div><div><div><div><div>The precedence= of "as" is not intuitive,<br></div>=C2=A0 [], _ as y<br></div>is= parsed as<br></div>=C2=A0 ([], _) as y<br></div>instead of, as you expecte= d<br></div>=C2=A0 [], (_ as y)<br></div>so the second line has a type error= (y has the wrong type).<br><br></div>I recommend parenthesizing explicitly= when using "as".<br></div><div class=3D"gmail_extra"><br><div cl= ass=3D"gmail_quote">On Sun, Nov 27, 2016 at 3:06 PM, Douglas Lewit <a href= =3D"mailto:[email protected]">[email protected]</a> [ocaml_beginners] <span= dir=3D"ltr"><<a href=3D"mailto:[email protected]" target= =3D"_blank">[email protected]</a>></span> wrote:<br><block= quote class=3D"gmail_quote" style=3D"border-left:1px #ccc solid;"> =20=20=20=20=20=20=20=20 <div> <br><br> <div dir=3D"ltr"><font size=3D"4">Hi everyone,</font><div><font size=3D"4">= <br></font></div><div><font size=3D"4">I created my own little riffle funct= ion.=C2=A0 It's similar ( but not exactly the same as ) Wolfram Mathema= tica's Riffle function.=C2=A0 Mathematica's Riffle output is limite= d by the length of the smaller list.=C2=A0 My riffle output's length is= determined by the length of the larger list.=C2=A0 A small difference real= ly.=C2=A0 Anyhow, here is my function:</font></div><div><font size=3D"4"><b= r></font></div><div><font size=3D"4"><div style=3D"font-weight:bold;">let r= iffle list1 list2 =3D let add_two_lists l1 l2 l3 =3D=C2=A0</div><div style= =3D"font-weight:bold;">=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 m= atch l1, l2 with=C2=A0</div><div style=3D"font-weight:bold;">=C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 |x, [ ] -> l3 @ x</div><div style= =3D"font-weight:bold;">=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 |= [ ], y -> l3 @ y</div><div style=3D"font-weight:bold;">=C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 |h1 :: t1, h2 :: t2 -> h1 :: h2 :: ad= d_two_lists t1 t2 l3 in=C2=A0</div><div style=3D"font-weight:bold;">=C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 add_two_lists list1 list2 [ ]= ;;</div><div style=3D"font-weight:bold;"><br></div><div>It works great!=C2= =A0 It works exactly as I want it to, BUT HERE'S THE PROBLEM.=C2=A0 The= following function DOES NOT EVEN COMPILE!!!!=C2=A0 Why????</div><div><br><= /div><div><div><b>let riffle list1 list2 =3D let add_two_lists l1 l2 l3 =3D= =C2=A0</b></div><div><b>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 match l1, l2 with=C2=A0</b></div><div><b>=C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 |_ as x, [ ] -> l3 @ x</b></div><div><b>=C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 |[ ], _ as y -> l3 @ y</b>= </div><div><b>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 |h1 :: t= 1, h2 :: t2 -> h1 :: h2 :: add_two_lists t1 t2 l3 in=C2=A0</b></div><div= ><b>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 add_two_lists list1= list2 [ ] ;;</b></div></div><div><b><br></b></div><div>Perhaps I do not fu= lly understand how to use the "as" keyword, but I thought that th= e two functions should compile and produce the exact same output.=C2=A0 Wha= t's the difference between the two forms?=C2=A0 I appreciate the feedba= ck!</div><div><br></div><div>Best,</div><div><br></div><div>Douglas Lewit.<= /div><div><br></div><div>P.S.=C2=A0 Can someone provide a simple example of= how to initialize and use a Map data structure?</div><div><br></div></font= ></div></div> <br> <br> <div width=3D"1" style=3D"color:white;"></div> </div></blockquote></div><br></div> </p> </div> 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