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From: Sebastian Fischer <sebf_at_informatik.uni-kiel.de>

Date: Wed, 25 Nov 2009 12:00:43 +0100

Hello,

it is well known that eta-expansion is not valid in functional-logic

programs [1]. To my surprise, this has the consequence that the same

is true for applications of lambda abstractions (due to the way they

are eliminated using lambda lifting). Here is an example session using

the Münster Curry Compiler, but PACKS behaves similarly (but does not

allow lambda abstractions in its prompt):

cyi> let twice f x = f (f x) in twice ((1?2)+) 10

12

More solutions? [Y(es)/n(o)/a(ll)]

14

cyi> let twice f x = f (f x) in twice ((\x -> \y -> x+y) (1?2)) 10

12

More solutions? [Y(es)/n(o)/a(ll)]

14

cyi> let twice f x = f (f x) in twice (\y -> (1?2)+y) 10

12

More solutions? [Y(es)/n(o)/a(ll)]

13

More solutions? [Y(es)/n(o)/a(ll)]

13

More solutions? [Y(es)/n(o)/a(ll)]

14

The second call is a (semantically valid, I think) translation of the

first partial application into lambda abstractions, the third call

results from the second by application which is - for me, surprisingly

- an invalid transformation.

I don't propose to change anything, just wanted to share this

observation.

Cheers,

Sebastian

[1]: http://www.informatik.uni-kiel.de/~curry/listarchive/0497.html

Date: Wed, 25 Nov 2009 12:00:43 +0100

Hello,

it is well known that eta-expansion is not valid in functional-logic

programs [1]. To my surprise, this has the consequence that the same

is true for applications of lambda abstractions (due to the way they

are eliminated using lambda lifting). Here is an example session using

the Münster Curry Compiler, but PACKS behaves similarly (but does not

allow lambda abstractions in its prompt):

cyi> let twice f x = f (f x) in twice ((1?2)+) 10

12

More solutions? [Y(es)/n(o)/a(ll)]

14

cyi> let twice f x = f (f x) in twice ((\x -> \y -> x+y) (1?2)) 10

12

More solutions? [Y(es)/n(o)/a(ll)]

14

cyi> let twice f x = f (f x) in twice (\y -> (1?2)+y) 10

12

More solutions? [Y(es)/n(o)/a(ll)]

13

More solutions? [Y(es)/n(o)/a(ll)]

13

More solutions? [Y(es)/n(o)/a(ll)]

14

The second call is a (semantically valid, I think) translation of the

first partial application into lambda abstractions, the third call

results from the second by application which is - for me, surprisingly

- an invalid transformation.

I don't propose to change anything, just wanted to share this

observation.

Cheers,

Sebastian

[1]: http://www.informatik.uni-kiel.de/~curry/listarchive/0497.html

-- Underestimating the novelty of the future is a time-honored tradition. (D.G.) _______________________________________________ curry mailing list curry_at_lists.RWTH-Aachen.DE http://MailMan.RWTH-Aachen.DE/mailman/listinfo/curryReceived on Wed Nov 25 2009 - 12:02:14 CET

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