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From: Michael Hanus <mh_at_informatik.uni-kiel.de>

Date: Wed, 05 Jan 2011 10:51:18 +0100

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).

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.

I am interested to get some feedback on this proposal.

Best regards,

Michael

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curry mailing list

curry_at_lists.RWTH-Aachen.DE

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

Received on Wed Jan 05 2011 - 11:04:45 CET

Date: Wed, 05 Jan 2011 10:51:18 +0100

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).

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.

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

Received on Wed Jan 05 2011 - 11:04:45 CET

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