Sorry there are two mailers on this machine Regards SCott ----- Original Message ----- From: "Jan Brosius" To: "Jon Cast" Cc: Sent: Monday, August 19, 2002 4:15 AM Subject: Fw: Question aboutthe use of an inner forall

Still some question: Ok a is not a type but Integer is a type . But a can be instantiated to integer. This comes pretty close to call a therefore a type variable, Isn't it?

And otherwise why writing forall a etc.

Regards

Scott

----- Original Message ----- From: "Scott J." To: "Jon Cast" Cc: Sent: Monday, August 19, 2002 4:09 AM Subject: Re: Question aboutthe use of an inner forall

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Still some question: Ok a is a type and Integer is a type . But a can be instantiated to integer. This comes pretty close to call a therefore a type variable.

Regards

Scott

----- Original Message ----- From: "Jon Cast" To: "Scott J." Cc: "Ashley Yakeley" ; Sent: Monday, August 19, 2002 3:48 AM Subject: Re: Question aboutthe use of an inner forall

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"Scott J." wrote:

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A question: s is not a type variable as a isn't it? I mean a can be of type Integer while s cannot.

Guessing at your question:

a has no type (and neither does s); it /is/ a type. In Haskell, types have kinds. And, both a and s have kind *.

Now then, the user can instantiate a to Integer, yes. And the user cannot instantiate s to anything---that's what the `forall' is for. runST will (theoretically) instantiate s to something. That could be Integer if the language implementors felt like it. The user of runST certainly has to be prepared for the possibility.

Does that come close to answering your question?

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Regards,

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Scott

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