Very confused about this.
"Douglas Lewit [email protected] [ocaml_beginners]" <[email protected]> Mon, 24 Jul 2017 20:04:11 -0500
| Newsgroups | gmane.comp.lang.ocaml.beginners |
|---|---|
| Message-ID | <CAM0XMJRLfQjC9FB3p4cZ4kj56S-ddquKAd=O82bVqiYZk7_yjg@mail.gmail.com> |
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Hi everyone,
So I'm working on this Klotski project, and I have to implement the
following type:
type ('a, 'set) set_operations =
{ empty : 'set ;
mem : 'a -> 'set -> bool ;
add : 'a -> 'set -> 'set ;
}
This is a project I'm doing for an independent study, but bear in mind my
professor does not OCaml. (Other than what I've shown him so far.)
So here's the thing. 'set could be of type list, right? That's probably
the most intuitive way to implement a set--a list without any repeated
elements.
So I could just do
*{ empty = [ ] ;*
* mem = let rec member x ls = match ls with *
* |[ ]
-> false *
* |head :: tail -> if
x = head *
*
then true *
*
else member x tail ;*
* (* Now here's the tricky part! *)*
* add = let addElement x ls = if not (member x ls) *
* then x :: ls *
* else failwith "Cannot add
element to set!" ;*
*}*
It's tricky because "add" requires a function that refers to mem's
function, which hasn't even been defined in memory yet!!! How can I work
around that? Do record objects in OCaml have some type of "this" (Java
style) or "self" (Python style) constructor? Thanks for the feedback.
Best,
Douglas.
P.S. Here I'm also assuming that functions can serve as record fields,
although I must confess that I have never seen that before. If someone can
help me get this type working, that would be GREAT!!! The type itself
compiles, but I need to understand how to create instances of this type.
Right now I'm a little lost with that. I appreciate the help.
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<p><div dir=3D"ltr"><font size=3D"4">Hi everyone,</font><div><font si=
ze=3D"4"><br></font></div><div><font size=3D"4">So I'm working on this =
Klotski project, and I have to implement the following type:</font></div><d=
iv><font size=3D"4"><br></font></div><div><font size=3D"4">type ('a, &#=
39;set) set_operations =3D=C2=A0</font></div><div><font size=3D"4">{ empty =
: 'set ;=C2=A0</font></div><div><font size=3D"4">=C2=A0 =C2=A0mem =C2=
=A0: 'a -> 'set -> bool ;=C2=A0</font></div><div><font size=
=3D"4">=C2=A0 =C2=A0add =C2=A0 =C2=A0: 'a -> 'set -> 'set=
;</font></div><div><font size=3D"4">}</font></div><div><font size=3D"4"><b=
r></font></div><div><font size=3D"4">This is a project I'm doing for an=
independent study, but bear in mind my professor does not OCaml. =C2=A0(Ot=
her than what I've shown him so far.)</font></div><div><font size=3D"4"=
><br></font></div><div><font size=3D"4">So here's the thing. =C2=A0'=
;set could be of type list, right?=C2=A0 That's probably the most intui=
tive way to implement a set--a list without any repeated elements.</font></=
div><div><font size=3D"4">So I could just do=C2=A0</font></div><div><font s=
ize=3D"4"><b>{ empty =3D [ ] ;</b></font></div><div><font size=3D"4"><b>=C2=
=A0 =C2=A0mem =3D let rec member x ls =3D match ls with=C2=A0</b></font></d=
iv><div><font size=3D"4"><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 =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 -> false=C2=A0</b></fon=
t></div><div><font size=3D"4"><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 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 |head :: tail =
=C2=A0 =C2=A0 -> =C2=A0if x =3D head=C2=A0</b></font></div><div><font si=
ze=3D"4"><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 =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 =C2=A0 =C2=A0 =C2=A0 then true=C2=
=A0</b></font></div><div><font size=3D"4"><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 =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 =C2=A0 =C2=A0 =C2=A0 else member x tail ;</b></font></div><div><font si=
ze=3D"4"><b>=C2=A0 (* Now here's the tricky part! *)</b></font></div><d=
iv><font size=3D"4"><b>=C2=A0 =C2=A0add =3D let addElement x ls =3D if not =
(member x ls)=C2=A0</b></font></div><div><font size=3D"4"><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 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 then x :: ls=C2=A0</b></font></div><div><font size=3D"4"><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 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 else failwith "Cannot add element to set!" ;</b></f=
ont></div><div><font size=3D"4"><b>}</b></font></div><div><font size=3D"4">=
<br></font></div><div><font size=3D"4">It's tricky because "add&qu=
ot; requires a function that refers to mem's function, which hasn't=
even been defined in memory yet!!!=C2=A0 How can I work around that?=C2=A0=
Do record objects in OCaml have some type of "this" (Java style)=
or "self" (Python style) constructor?=C2=A0 Thanks for the feedb=
ack.</font></div><div><font size=3D"4"><br></font></div><div><font size=3D"=
4">Best,</font></div><div><font size=3D"4"><br></font></div><div><font size=
=3D"4">Douglas.</font></div><div><font size=3D"4"><br></font></div><div><fo=
nt size=3D"4">P.S.=C2=A0 Here I'm also assuming that functions can serv=
e as record fields, although I must confess that I have never seen that bef=
ore.=C2=A0 If someone can help me get this type working, that would be GREA=
T!!!=C2=A0 The type itself compiles, but I need to understand how to create=
instances of this type.=C2=A0 Right now I'm a little lost with that.=
=C2=A0 I appreciate the help.</font></div><div><font size=3D"4"><br></font>=
</div><div><font size=3D"4"><br></font></div></div>
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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-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;
}=20
#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;=20
}=20
-->
</style>
</head>
<!--~-|**|PrettyHtmlEnd|**|-~-->
</html>
<!-- end group email -->
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