Re: Typechecking union types

Hans-Peter Diettrich <DrDiettrich@compuserve.de>
5 Jul 2006 15:15:42 -0400

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Related articles
Typechecking union types tc@elvis.dk (Thomas Christensen) (2006-06-27)
Re: Typechecking union types cwarren89@gmail.com (Curtis W) (2006-07-05)
Re: Typechecking union types DrDiettrich@compuserve.de (Hans-Peter Diettrich) (2006-07-05)
Re: Typechecking union types haberg@math.su.se (2006-07-05)
Re: Typechecking union types tc@elvis.dk (Thomas Christensen) (2006-07-28)
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From: Hans-Peter Diettrich <DrDiettrich@compuserve.de>
Newsgroups: comp.compilers
Date: 5 Jul 2006 15:15:42 -0400
Organization: Compilers Central
References: 06-06-072
Keywords: types
Posted-Date: 05 Jul 2006 15:15:42 EDT

Thomas Christensen wrote:


> For my master thesis, I need to get up to speed
> on the current state of the art within the somewhat
> narrow field of typechecking union types.
...
> What I need is some background on the various problems/issues related
> specifically to union types.


IMO the most important question is:


Is a union kind of implicit type cast, or can it hold polymorphic
(variant) information, but only one kind at a time.


As Wirth possibly had in mind with the tag field in Pascal variant
records, or as actually implemented in (Windows) Variant types, a
compiler could at least add a hidden information about the last
written "branch" of a union. When such techniques are used, the
problems should go away.


DoDi

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