Different types with equal fieldsThis is a discussion on Different types with equal fields within the ml forums in Programming Languages category; I have a problem :-D. I need to define two different types point2 and point3: type point2 = {x:float; y:float} type point3 = {x:float; y:float; z:float} Because I need to make operations with 2d & 3d points. The problem is when I need to create a point2 variable: # {x=0.;y=0.};; Some record field labels are undefined: z # let (p : point2) = {x=0.; y=0.};; Some record field labels are undefined: z Creating a point3 variable I have no problem: # {x=0.;y=0.;z=0.};; - : point3 = {x = 0.; y = 0.; z = 0.} Ocaml cannot differentiate between point2 ... | ||||||||
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#1
08-05-2003, 04:28 PM
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 Different types with equal fields I have a problem :-D. I need to define two different types point2 and point3: type point2 = {x:float; y:float} type point3 = {x:float; y:float; z:float} Because I need to make operations with 2d & 3d points. The problem is when I need to create a point2 variable: # {x=0.;y=0.};; Some record field labels are undefined: z # let (p : point2) = {x=0.; y=0.};; Some record field labels are undefined: z Creating a point3 variable I have no problem: # {x=0.;y=0.;z=0.};; - : point3 = {x = 0.; y = 0.; z = 0.} Ocaml cannot differentiate between point2 & point3 types. How I can make a point2 variable?  |
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#2
08-05-2003, 05:49 PM
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| Re: Different types with equal fields It's a FAQ: http://caml.inria.fr/FAQ/FAQ_EXPERT-...bels_surcharge On Tue, 5 Aug 2003 20:28:26 +0000 (UTC), samsaga2 <samsaga2@menta.net> wrote: > I have a problem :-D. I need to define two different types point2 and point3: > > type point2 = {x:float; y:float} > type point3 = {x:float; y:float; z:float} > > Ocaml cannot differentiate between point2 & point3 types. How I can make > a point2 variable? |
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#3
08-12-2003, 07:01 PM
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| Re: Different types with equal fields In article <bgu0nd$1v5$1@wolfberry.srv.cs.cmu.edu>, Rob Arthan wrote: > Julian Brown wrote: > >> In article <bgp41a$k6d$1@wolfberry.srv.cs.cmu.edu>, samsaga2 wrote: >>> I have a problem :-D. I need to define two different types point2 and >>> point3: >>> >>> type point2 = {x:float; y:float} >>> type point3 = {x:float; y:float; z:float} >>> >>> Because I need to make operations with 2d & 3d points. The problem is >>> when I need to create a point2 variable: >>> >>> # {x=0.;y=0.};; >>> Some record field labels are undefined: z >>> >>> # let (p : point2) = {x=0.; y=0.};; >>> Some record field labels are undefined: z >>> >>> Creating a point3 variable I have no problem: >>> >>> # {x=0.;y=0.;z=0.};; >>> - : point3 = {x = 0.; y = 0.; z = 0.} >>> >>> Ocaml cannot differentiate between point2 & point3 types. How I can make >>> a point2 variable? >> >> This is in the FAQ, see: >> >> http://caml.inria.fr/FAQ/FAQ_EXPERT-...bels_surcharge >> >> Jules > > Yucch! This is how really prehistoric C compilers treated structure member > names - and it's a feature in Ocaml? It is pretty gruesome I think, but at least the scope for member names is only the current module (ie, source file under normal circumstances, unless you "open" things or make sub-modules as in the FAQ entry). Possibly, alternatives would involve nasty (from the compiler's point of view) context-sensitivity in the syntax. How would you prefer it to work? Better stop before I get way out of my depth ;-) Jules |
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