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From: db@lfcs.ed.ac.uk (Dave Berry)
Newsgroups: comp.lang.misc
Subject: Re: Polymorphism
Message-ID: <1899@etive.ed.ac.uk>
Date: 2 May 89 13:33:31 GMT
References: <5957@pdn.paradyne.com< <1810@etive.ed.ac.uk< <5973@pdn.paradyne.com< <1834@etive.ed.ac.uk> <6000@pdn.paradyne.com> <1859@etive.ed.ac.uk> <6032@pdn.paradyne.com>
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Reply-To: db@lfcs.ed.ac.uk (Dave Berry)
Organization: Laboratory for the Foundations of Computer Science, Edinburgh U
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><In article <6000@pdn.paradyne.com> alan@rnms1.paradyne.com (Alan Lovejoy) writes:
><>It should be pointed out, however, that there is no inherent reason that
><>function-values cannot or should not be compared for equality.  

That depends on what you mean by equality.  If you are happy for the
expression "fn x => 1  =  fn x => 1" to return false, then you can define
equality by comparing the address of function in the computer.  Logically,
however, this isn't the definition of equality that one usually wants.

In article <6032@pdn.paradyne.com> alan@oz.paradyne.com (Alan Lovejoy) writes:
>In article <1859@etive.ed.ac.uk< nick@lfcs.ed.ac.uk (Nick Rothwell) writes:
>
><	let i = 1
><	in  (let i = 2 in i end, i)
><	end;
>
><there's no assignment going on here; just a (local) rebinding of the name.
><If it was assignment, the value of the above expression would be (2, 2),
><not (2, 1).
>
>Of course.  But there is a data structure (not "i") that IS being dynamically
>updated in place in your example: the dictionary that maps names to values.

That depends on the implementation, doesn't it?  It's quite possible to
implement a symbol table functionally, right down to special hardware if
you want to take it that far.

>Whether this updating actually occurs at run time or compile time is a feature
>of the implementation, not a property of the language definition.

It's nothing to do with run-time.  The symbol table is in the compiler.
Furthermore, your argument that something occurring in an implementation
justifies a statement about the language being implemented seems completely
bogus to me.  Statements about a language should be judged by the semantics
of that language, not by the way some people might choose to implement it
on some hardware.

 "See, this is why I got off drugs.  Who can tell the difference anymore?"
Dave Berry,	Laboratory for Foundations of Computer Science, Edinburgh.
		db%lfcs.ed.ac.uk@nsfnet-relay.ac.uk
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