Re: Very confused about this.
"Florent Monnier [email protected] [ocaml_beginners]" <[email protected]> Mon, 24 Jul 2017 20:30:31 -0700
| Newsgroups | gmane.comp.lang.ocaml.beginners |
|---|---|
| Message-ID | <CAE1DttDJgcu_wuBquniPDcXFgdp17J6=VLvAoNEcX_0R8wefaw@mail.gmail.com> |
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Hi,
Just create the functions first, and then set it into your type, just like =
this:
# let rec member x ls =3D
match ls with
| [] -> false
| head::tail ->
if x =3D head then true
else member x tail
;;
val member : 'a -> 'a list -> bool =3D <fun>
# let addElement x ls =3D
if not (member x ls)
then x :: ls
else failwith "Cannot add element to set!" ;;
val addElement : 'a -> 'a list -> 'a list =3D <fun>
# { empty =3D [];
mem =3D member;
add =3D addElement;
} ;;
--=20
2017-07-24 18:04 UTC=E2=88=9207:00, Douglas Lewit [email protected]
[ocaml_beginners] <[email protected]>:
> Hi everyone,
>
> So I'm working on this Klotski project, and I have to implement the
> following type:
>
> type ('a, 'set) set_operations =3D
> { 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 =3D [ ] ;*
> * mem =3D let rec member x ls =3D match ls with *
> * |[ ]
> -> false *
> * |head :: tail -> =
if
> x =3D head *
> *
> then true *
> *
> else member x tail ;*
> * (* Now here's the tricky part! *)*
> * add =3D let addElement x ls =3D if not (member x ls) *
> * then x :: ls *
> * else failwith "Cannot ad=
d
> 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 c=
an
> 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>Hi,<br>
Just create the functions first, and then set it into your type, just like =
this:<br>
# let rec member x ls =3D<br>
match ls with<br>
| [] -> false<br>
| head::tail -><br>
if x =3D head then true<br>
else member x tail<br>
;;<br>
val member : 'a -> 'a list -> bool =3D <fun><br>
# let addElement x ls =3D<br>
if not (member x ls)<br>
then x :: ls<br>
else failwith "Cannot add element to set!" ;;<br>
val addElement : 'a -> 'a list -> 'a list =3D <fun>=
<br>
# { empty =3D [];<br>
mem =3D member;<br>
add =3D addElement;<br>
} ;;<br>
<br>
-- <br>
2017-07-24 18:04 UTC=E2=88=9207:00, Douglas Lewit [email protected]<br>
[ocaml_beginners] <[email protected]>:<br>
> Hi everyone,<br>
><br>
> So I'm working on this Klotski project, and I have to implement th=
e<br>
> following type:<br>
><br>
> type ('a, 'set) set_operations =3D<br>
> { empty : 'set ;<br>
> mem : 'a -> 'set -> bool ;<br>
> add : 'a -> 'set -> 'set ;<br>
> }<br>
><br>
> This is a project I'm doing for an independent study, but bear in =
mind my<br>
> professor does not OCaml. (Other than what I've shown him so far.=
)<br>
><br>
> So here's the thing. 'set could be of type list, right? That=
's probably<br>
> the most intuitive way to implement a set--a list without any repeated=
<br>
> elements.<br>
> So I could just do<br>
> *{ empty =3D [ ] ;*<br>
> * mem =3D let rec member x ls =3D match ls with *<br>
> * |[ ]<br>
> -> false *<br>
> * |head :: tail -=
> if<br>
> x =3D head *<br>
> *<br>
> then true *<br>
> *<br>
> else member x tail ;*<br>
> * (* Now here's the tricky part! *)*<br>
> * add =3D let addElement x ls =3D if not (member x ls) *<br>
> * then x :: ls *<br>
> * else failwith "C=
annot add<br>
> element to set!" ;*<br>
> *}*<br>
><br>
> It's tricky because "add" requires a function that refer=
s to mem's<br>
> function, which hasn't even been defined in memory yet!!! How can=
I work<br>
> around that? Do record objects in OCaml have some type of "this&=
quot; (Java<br>
> style) or "self" (Python style) constructor? Thanks for the=
feedback.<br>
><br>
> Best,<br>
><br>
> Douglas.<br>
><br>
> P.S. Here I'm also assuming that functions can serve as record fi=
elds,<br>
> although I must confess that I have never seen that before. If someon=
e can<br>
> help me get this type working, that would be GREAT!!! The type itself=
<br>
> compiles, but I need to understand how to create instances of this typ=
e.<br>
> Right now I'm a little lost with that. I appreciate the help.<br>
><br>
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