segments->painter fails with list from #lang sicp about sicp HOT 10 CLOSED

That's a regression caused by me (see ce24736). I will push a fix soon, and you should be able to switch back to #lang sicp after that (feel free to keep using #lang racket, too!)

from sicp.

Hi Rick,

This is a bit subtle. The language #lang sicp uses mutable pairs while
#lang racket uses immutable pairs.
If you create a list in #lang sicp you will get a list consisting of
mutable pairs (printed as mcons) and
since the segments->painter is expecting a Racket list consisting of
immutable pairs (printed as cons) you get
the error.

Best advice: Use #lang racket to work with the painter language.

/Jens Axel

2016-03-26 12:55 GMT+01:00 Rick van de Loo [email protected]:

Hi,

I ran into a problem while doing exercise 2.49 from SICP. The
segments->painter procedure from prmpnt.scm gives a contract violation if
it's given a list defined in the sicp lang.

#lang sicp
(#%require sicp-pict)

(define (make-vect x y)
(cons x y))

(define (xcor-vect vect)
(car vect))

(define (ycor-vect vect)
(cdr vect))

(define (make-segment vect-origin-to-start vect-origin-to-end)
(cons vect-origin-to-start vect-origin-to-end))

(define outline-segments
(segments->painter
(list ; <- culprit
(make-segment (make-vect 0.0 0.0) (make-vect 0.0 0.99))
(make-segment (make-vect 0.0 0.0) (make-vect 0.99 0.0))
(make-segment (make-vect 0.99 0.0) (make-vect 0.99 0.99))
(make-segment (make-vect 0.0 0.99) (make-vect 0.99 0.99)))))

(paint outline-segments)

for-each: contract violation
expected: list?
given: (mcons (mcons '(0.0 . 0.0) '(0.0 . 0.99)) (mcons (mcons '(0.0 . 0.0) '(0.99 . 0.0)) (mcons (mcons '(0.99 . 0.0) '(0.99 . 0.99)) (mcons (mcons '(0.0 . 0.99) '(0.99 . 0.99)) '()))))
argument position: 2nd

The violation occurs here
https://github.com/sicp-lang/sicp/blob/master/sicp-pict/prmpnt.scm#L114.
The snippet above works if instead of using #lang sicp, #lang racket/base
is used.

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#4

Jens Axel Søgaard

from sicp.

I'll see if I can get segments->painter to accept both kind of lists.

/Jens Axel

2016-03-26 14:29 GMT+01:00 Jens Axel Søgaard [email protected]:

Hi Rick,

This is a bit subtle. The language #lang sicp uses mutable pairs while
#lang racket uses immutable pairs.
If you create a list in #lang sicp you will get a list consisting of
mutable pairs (printed as mcons) and
since the segments->painter is expecting a Racket list consisting of
immutable pairs (printed as cons) you get
the error.

Best advice: Use #lang racket to work with the painter language.

/Jens Axel

2016-03-26 12:55 GMT+01:00 Rick van de Loo [email protected]:

Hi,

I ran into a problem while doing exercise 2.49 from SICP. The
segments->painter procedure from prmpnt.scm gives a contract violation if
it's given a list defined in the sicp lang.

#lang sicp
(#%require sicp-pict)

(define (make-vect x y)
(cons x y))

(define (xcor-vect vect)
(car vect))

(define (ycor-vect vect)
(cdr vect))

(define (make-segment vect-origin-to-start vect-origin-to-end)
(cons vect-origin-to-start vect-origin-to-end))

(define outline-segments
(segments->painter
(list ; <- culprit
(make-segment (make-vect 0.0 0.0) (make-vect 0.0 0.99))
(make-segment (make-vect 0.0 0.0) (make-vect 0.99 0.0))
(make-segment (make-vect 0.99 0.0) (make-vect 0.99 0.99))
(make-segment (make-vect 0.0 0.99) (make-vect 0.99 0.99)))))

(paint outline-segments)

for-each: contract violation
expected: list?
given: (mcons (mcons '(0.0 . 0.0) '(0.0 . 0.99)) (mcons (mcons '(0.0 . 0.0) '(0.99 . 0.0)) (mcons (mcons '(0.99 . 0.0) '(0.99 . 0.99)) (mcons (mcons '(0.0 . 0.99) '(0.99 . 0.99)) '()))))
argument position: 2nd

The violation occurs here
https://github.com/sicp-lang/sicp/blob/master/sicp-pict/prmpnt.scm#L114.
The snippet above works if instead of using #lang sicp, #lang racket/base
is used.

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#4

Jens Axel Søgaard

Jens Axel Søgaard

from sicp.

This commit
0da6a81

fixes the problem.

Update the sicp package either using raco or the DrRacket package manager
to get the changes.

Thanks for the bug report.

/Jens Axel

2016-03-26 14:36 GMT+01:00 Jens Axel Søgaard [email protected]:

I'll see if I can get segments->painter to accept both kind of lists.

/Jens Axel

2016-03-26 14:29 GMT+01:00 Jens Axel Søgaard [email protected]:

Hi Rick,

This is a bit subtle. The language #lang sicp uses mutable pairs while
#lang racket uses immutable pairs.
If you create a list in #lang sicp you will get a list consisting of
mutable pairs (printed as mcons) and
since the segments->painter is expecting a Racket list consisting of
immutable pairs (printed as cons) you get
the error.

Best advice: Use #lang racket to work with the painter language.

/Jens Axel

2016-03-26 12:55 GMT+01:00 Rick van de Loo [email protected]:

Hi,

I ran into a problem while doing exercise 2.49 from SICP. The
segments->painter procedure from prmpnt.scm gives a contract violation if
it's given a list defined in the sicp lang.

#lang sicp
(#%require sicp-pict)

(define (make-vect x y)
(cons x y))

(define (xcor-vect vect)
(car vect))

(define (ycor-vect vect)
(cdr vect))

(define (make-segment vect-origin-to-start vect-origin-to-end)
(cons vect-origin-to-start vect-origin-to-end))

(define outline-segments
(segments->painter
(list ; <- culprit
(make-segment (make-vect 0.0 0.0) (make-vect 0.0 0.99))
(make-segment (make-vect 0.0 0.0) (make-vect 0.99 0.0))
(make-segment (make-vect 0.99 0.0) (make-vect 0.99 0.99))
(make-segment (make-vect 0.0 0.99) (make-vect 0.99 0.99)))))

(paint outline-segments)

for-each: contract violation
expected: list?
given: (mcons (mcons '(0.0 . 0.0) '(0.0 . 0.99)) (mcons (mcons '(0.0 . 0.0) '(0.99 . 0.0)) (mcons (mcons '(0.99 . 0.0) '(0.99 . 0.99)) (mcons (mcons '(0.0 . 0.99) '(0.99 . 0.99)) '()))))
argument position: 2nd

The violation occurs here
https://github.com/sicp-lang/sicp/blob/master/sicp-pict/prmpnt.scm#L114.
The snippet above works if instead of using #lang sicp, #lang
racket/base is used.

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#4

Jens Axel Søgaard

Jens Axel Søgaard

Jens Axel Søgaard

from sicp.

Great! Thanks for the quick reply :)

from sicp.

GOOD GRIEF! I spent a whole day wondering what in the world was wrong with my code.

Thank you for the question and the answer. I wish I had checked sooner.

I can concur that declaring #lang racket instead of #lang sicp is the fix.

I pushed a commit to my repo, fixing the language declaration, and with details in the commit message.

Use 'racket', not 'sicp' in ex2-44 picture lang file adityaathalye/sicp@c8b62c3

from sicp.

Hmm. Provided that @soegaard made segments->painter to accept both mutable and immutable lists, there should not be any problem, right? Can you provide us a code example that leads to a problem?

from sicp.

Hmm. Provided that @soegaard made segments->painter to accept both mutable and immutable lists, there should not be any problem, right? Can you provide us a code example that leads to a problem?

Updated my earlier comment to keep things in context: #4 (comment)

from sicp.

I believe this is fixed by 4152068. Closing. Feel free to reopen it if you find any other issues.

from sicp.

I just updated lang-sicp locally and can confirm SHA 4152068 fixes the bug. Thank you!

from sicp.