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From: Sergio Antoy <antoy_at_cs.pdx.edu>

Date: Wed, 05 Jan 2011 10:56:08 -0800

On Wed, 05 Jan 2011, Michael Hanus wrote:

* > Dear Colleagues,
*

* >
*

* > I'd like to propose two slight syntax extensions to the current definition
*

* > of Curry that I found useful to make programs more readable
*

* > from my practical experiences.
*

* >
*

* > 1. Anonymous free variables: allow anonymous variables of the form "_"
*

* > (underscore) in arbitrary expressions. Currently, anonymous variables
*

* > are only allowed in patterns but not as free variables in right-hand
*

* > sides or condition of rules. This has the drawback that they
*

* > must be explicitly declared or one has to use the Prelude
*

* > operation "unknown". Both is not nicely readable if one has
*

* > several unknown arguments to some operation f:
*

* > let a,b,c,d,e free in f x a b c d e
*

* > or
*

* > f x unknown unknown unknown unknown unknown
*

* > With the proposed extension, one can simply write "f x _ _ _ _ _"
*

* > Thus, an occurrence of "_" in an expression is syntactic sugar
*

* > for "let x free in x" (or the operation Prelude.unknown).
*

Yes. It is welcome and long overdue.

* > 2. Non-linear patterns in function declarations: allow multiple occurences
*

* > of a same variable in left-hand sides of function declarations.
*

* > Such occurrences are syntactic sugar for equational constraints,
*

* > i.e., a rule like "f x y (C x) = rhs" is syntactic sugar for
*

* > "f x y (C z) | x=:=z = rhs" where z is a fresh variable.
*

* > This extension avoids a restriction in Curry compared to logic programming.
*

* > Moreover, the linearity condition does not make much sense
*

* > in the light of other useful extensions like functional patterns.
*

* > Finally, I don't see what is really gained by the linearity restriction.
*

Yes. One could also have x==z. Why is x=:=z preferred?

In true FLP there should be (almost) no residuation. But

since there is residuation in Curry, all options should be

considered and the chosen one justified.

* > I am interested to get some feedback on this proposal.
*

* >
*

* > Best regards,
*

* >
*

* > Michael
*

* > _______________________________________________
*

* > curry mailing list
*

* > curry_at_lists.RWTH-Aachen.DE
*

* > http://MailMan.RWTH-Aachen.DE/mailman/listinfo/curry
*

Best,

Sergio

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Received on Do Jan 06 2011 - 09:09:24 CET

Date: Wed, 05 Jan 2011 10:56:08 -0800

On Wed, 05 Jan 2011, Michael Hanus wrote:

Yes. It is welcome and long overdue.

Yes. One could also have x==z. Why is x=:=z preferred?

In true FLP there should be (almost) no residuation. But

since there is residuation in Curry, all options should be

considered and the chosen one justified.

Best,

Sergio

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curry mailing list

curry_at_lists.RWTH-Aachen.DE

http://MailMan.RWTH-Aachen.DE/mailman/listinfo/curry

Received on Do Jan 06 2011 - 09:09:24 CET

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