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Date: Sun, 20 Dec 2009 12:44:57 -0500
Message-ID: <f74178430912200944w28145e73vebbe43912fcc5ea4@mail.gmail.com>
Subject: obj.magic for polymorphic record fields
From: Jacques Le Normand <rathereasy@gmail.com>
To: caml-list caml-list <caml-list@yquem.inria.fr>
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X-Spam: no; 0.00; ocaml-list:01 foo:01 baz:01 ocaml-list:01 foo:01 baz:01 polymorphic:01 polymorphic:01 int:01 int:01 jacques:03 jacques:03 let:03 let:03 fun:08 

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Dear ocaml-list,
the following code does not type check:

type foo = {bar : 'a. 'a -> 'a}
let a : int -> int = fun x -> x
let baz = {bar = Obj.magic a}

with the error

Error: This field value has type 'a -> 'a which is less general than
         'b. 'b -> 'b


my question is: how could I use obj.magic to get a polymorphic type?


Jacques

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Dear ocaml-list,<div>the following code does not type check:</div><div><br>=
</div><div><div>type foo =3D {bar : &#39;a. &#39;a -&gt; &#39;a}</div><div>=
let a : int -&gt; int =3D fun x -&gt; x</div><div>let baz =3D {bar =3D Obj.=
magic a}</div>
<div><br></div><div>with the error</div><div><br></div><div><div>Error: Thi=
s field value has type &#39;a -&gt; &#39;a which is less general than</div>=
<div>=A0=A0 =A0 =A0 =A0 &#39;b. &#39;b -&gt; &#39;b</div><div><br></div><di=
v><br>
</div><div>my question is: how could I use obj.magic to get a polymorphic t=
ype?</div><div><br></div><div><br></div><div>Jacques</div></div></div>

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