* bug#26106: Defining a method named '-' with one parameter
@ 2017-03-15 13:35 Alejandro Sanchez
2017-04-19 15:00 ` Andy Wingo
0 siblings, 1 reply; 2+ messages in thread
From: Alejandro Sanchez @ 2017-03-15 13:35 UTC (permalink / raw)
To: 26106
If I define a method named ‘-‘ which only takes in one parameter, the expression ‘(- v)’ gets rewritten to ‘(- 0 v)’. Here is a minimal example:
(use-modules (oop goops))
(define-class <vector2> ()
(x #:init-value 0 #:getter get-x #:init-keyword #:x)
(y #:init-value 0 #:getter get-y #:init-keyword #:y))
(define-method (* (n <number>) (v <vector2>))
(make <vector2> #:x (* n (get-x v)) #:y (* n (get-y v))))
(define-method (- (v <vector2>))
(* -1 v))
(define v (make <vector2> #:x 1 #:y 2))
(* -1 v) ; Works fine
(- v) ; Throws error
Here is the error message:
scheme@(guile-user)> (- v)
ERROR: In procedure scm-error:
ERROR: No applicable method for #<<generic> - (2)> in call (- 0 #<<vector2> 10a8e4020>)
Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
scheme@(guile-user) [1]> ,bt
In current input:
23:0 2 (_)
In oop/goops.scm:
1438:4 1 (cache-miss 0 #<<vector2> 10a8e4020>)
In unknown file:
0 (scm-error goops-error #f "No applicable method for ~S in call ~S" (#<<generic> - (2)> (- 0 #<<vec…>)) #)
^ permalink raw reply [flat|nested] 2+ messages in thread
* bug#26106: Defining a method named '-' with one parameter
2017-03-15 13:35 bug#26106: Defining a method named '-' with one parameter Alejandro Sanchez
@ 2017-04-19 15:00 ` Andy Wingo
0 siblings, 0 replies; 2+ messages in thread
From: Andy Wingo @ 2017-04-19 15:00 UTC (permalink / raw)
To: Alejandro Sanchez; +Cc: 26106
On Wed 15 Mar 2017 14:35, Alejandro Sanchez <hiphish@openmailbox.org> writes:
> If I define a method named ‘-‘ which only takes in one parameter, the expression ‘(- v)’ gets rewritten to ‘(- 0 v)’. Here is a minimal example:
>
> (use-modules (oop goops))
>
> (define-class <vector2> ()
> (x #:init-value 0 #:getter get-x #:init-keyword #:x)
> (y #:init-value 0 #:getter get-y #:init-keyword #:y))
>
> (define-method (* (n <number>) (v <vector2>))
> (make <vector2> #:x (* n (get-x v)) #:y (* n (get-y v))))
>
> (define-method (- (v <vector2>))
> (* -1 v))
>
> (define v (make <vector2> #:x 1 #:y 2))
> (* -1 v) ; Works fine
> (- v) ; Throws error
>
> Here is the error message:
>
> scheme@(guile-user)> (- v)
> ERROR: In procedure scm-error:
> ERROR: No applicable method for #<<generic> - (2)> in call (- 0 #<<vector2> 10a8e4020>)
>
> Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
> scheme@(guile-user) [1]> ,bt
> In current input:
> 23:0 2 (_)
> In oop/goops.scm:
> 1438:4 1 (cache-miss 0 #<<vector2> 10a8e4020>)
> In unknown file:
> 0 (scm-error goops-error #f "No applicable method for ~S in call ~S" (#<<generic> - (2)> (- 0 #<<vec…>)) #)
Is (- x) equivalent to (* x -1) ?
Right now there are a few things happening. The "primitive expansion"
phase in an early part of the compiler turns (- x) to (- 0 x), where
obviously it should not be doing that. But can it turn it into (* x -1)
? Note that somewhat confusingly, a later part of the compiler that can
detect when X is a real number will undo that transformation, turning it
to (- 0 x) when X is real. So that sounds OK from an optimization point
of view but is the (* x -1) tranformation correct from the math point of
view?
Andy
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