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From: Sergio Antoy <antoy_at_cs.pdx.edu>

Date: Tue, 4 Feb 1997 11:59:41 -0800

Dear Curritos,

Thanks for all the answers that I got from my enquiry regarding

the soundness of the Madrid calculus for non-deterministic

functions. Your messages were helpfull and I understand the

calculus much better now.

At the cost of being a bit crude, I would summarize the discussion

as following. Given a TRS R, a value of f(t1,...tn) is a normal

form (w.r.t. R) of f(v1,...vn) for all the values v1,...vn of

t1,...tn respectively. This must be refined, since the calculus

computes the value of f(t1,...tn) even when some ti has no value,

if the value of ti is not needed, but with more accuracy, both

simplicity and intuition go.

This definition is reasonable and, of course, not all narrowing

strategies are sound for this definition, as the double(coin)

example shows. The existence of a sound and complete strategy for

this definition in non-confluent, non-terminating systems is not

at all obvious, and the Madrid group did a great job.

Has anyone investigated an alternative notion of value? E.g.,

values and data terms (constructor normal forms) coincide. This

definition is simpler and would allow more computations, such as

the ``many_solutions'' example of a previous posting. The

difference between the two alternatives seems to boil down to the

difference between call-by-value and call-by-name. Does anyone

see major advantages or disadvantages of the latter? A simpler

semantics is an advantage. The existence of a sound, complete,

and efficient strategy for it is not obvious.

Finally, is Hussmann's work online? I did a Web search, but I

could not find it.

Thanks again,

Sergio

--------------------------------

Sergio Antoy

Dept. of Computer Science

Portland State University

P.O.Box 751

Portland, OR 97207

voice +1 (503) 725-3009

fax +1 (503) 725-3211

internet antoy_at_cs.pdx.edu

WWW http://www.cs.pdx.edu/~antoy

--------------------------------

Received on Wed Feb 05 1997 - 08:25:54 CET

Date: Tue, 4 Feb 1997 11:59:41 -0800

Dear Curritos,

Thanks for all the answers that I got from my enquiry regarding

the soundness of the Madrid calculus for non-deterministic

functions. Your messages were helpfull and I understand the

calculus much better now.

At the cost of being a bit crude, I would summarize the discussion

as following. Given a TRS R, a value of f(t1,...tn) is a normal

form (w.r.t. R) of f(v1,...vn) for all the values v1,...vn of

t1,...tn respectively. This must be refined, since the calculus

computes the value of f(t1,...tn) even when some ti has no value,

if the value of ti is not needed, but with more accuracy, both

simplicity and intuition go.

This definition is reasonable and, of course, not all narrowing

strategies are sound for this definition, as the double(coin)

example shows. The existence of a sound and complete strategy for

this definition in non-confluent, non-terminating systems is not

at all obvious, and the Madrid group did a great job.

Has anyone investigated an alternative notion of value? E.g.,

values and data terms (constructor normal forms) coincide. This

definition is simpler and would allow more computations, such as

the ``many_solutions'' example of a previous posting. The

difference between the two alternatives seems to boil down to the

difference between call-by-value and call-by-name. Does anyone

see major advantages or disadvantages of the latter? A simpler

semantics is an advantage. The existence of a sound, complete,

and efficient strategy for it is not obvious.

Finally, is Hussmann's work online? I did a Web search, but I

could not find it.

Thanks again,

Sergio

--------------------------------

Sergio Antoy

Dept. of Computer Science

Portland State University

P.O.Box 751

Portland, OR 97207

voice +1 (503) 725-3009

fax +1 (503) 725-3211

internet antoy_at_cs.pdx.edu

WWW http://www.cs.pdx.edu/~antoy

--------------------------------

Received on Wed Feb 05 1997 - 08:25:54 CET

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