How do I pass (not f) as an f?
I have a filter function that takes in a predicate like odd?
and processes a list. Here is the code
(define (manual-filter f? lst)
(cond
[(empty? lst) empty]
[(f? (first lst)) (cons (first lst) (manual-filter f? (rest lst)))]
[else (manual-filter f? (rest lst))]))
How do I go about passing (not (f?)) as the function?
scheme racket
asked Nov 24 '18 at 23:44
SyvashSyvash
41
add a comment |
I have a filter function that takes in a predicate like odd?
and processes a list. Here is the code
(define (manual-filter f? lst)
(cond
[(empty? lst) empty]
[(f? (first lst)) (cons (first lst) (manual-filter f? (rest lst)))]
[else (manual-filter f? (rest lst))]))
How do I go about passing (not (f?)) as the function?
scheme racket
asked Nov 24 '18 at 23:44
SyvashSyvash
41
(define even? (compose not odd?))?
– Sylwester
Nov 25 '18 at 0:22
it's for a homework question so we can't use abstract functions such as compose, and odd? was an example, it could be any predicate
– Syvash
Nov 25 '18 at 0:24
add a comment |
I have a filter function that takes in a predicate like odd?
and processes a list. Here is the code
(define (manual-filter f? lst)
(cond
[(empty? lst) empty]
[(f? (first lst)) (cons (first lst) (manual-filter f? (rest lst)))]
[else (manual-filter f? (rest lst))]))
How do I go about passing (not (f?)) as the function?
scheme racket
asked Nov 24 '18 at 23:44
SyvashSyvash
41
I have a filter function that takes in a predicate like odd?
and processes a list. Here is the code
(define (manual-filter f? lst)
(cond
[(empty? lst) empty]
[(f? (first lst)) (cons (first lst) (manual-filter f? (rest lst)))]
[else (manual-filter f? (rest lst))]))
How do I go about passing (not (f?)) as the function?
scheme racket
scheme racket
asked Nov 24 '18 at 23:44
SyvashSyvash
41
asked Nov 24 '18 at 23:44
SyvashSyvash
41
asked Nov 24 '18 at 23:44
SyvashSyvash
41
asked Nov 24 '18 at 23:44
SyvashSyvash
41
asked Nov 24 '18 at 23:44
SyvashSyvash
41
41
(define even? (compose not odd?))?
– Sylwester
Nov 25 '18 at 0:22
it's for a homework question so we can't use abstract functions such as compose, and odd? was an example, it could be any predicate
– Syvash
Nov 25 '18 at 0:24
add a comment |
(define even? (compose not odd?))?
– Sylwester
Nov 25 '18 at 0:22
it's for a homework question so we can't use abstract functions such as compose, and odd? was an example, it could be any predicate
– Syvash
Nov 25 '18 at 0:24
(define even? (compose not odd?))?– Sylwester
Nov 25 '18 at 0:22
(define even? (compose not odd?))?– Sylwester
Nov 25 '18 at 0:22
it's for a homework question so we can't use abstract functions such as compose, and odd? was an example, it could be any predicate
– Syvash
Nov 25 '18 at 0:24
it's for a homework question so we can't use abstract functions such as compose, and odd? was an example, it could be any predicate
– Syvash
Nov 25 '18 at 0:24
add a comment |
2 Answers
2
active
oldest
votes
the not function has the signature Any -> Boolean. And is essentially:
(define (not x)
(if (eq? x #f) #t #f))
What you are looking for is a function that inverts the output to another given function. (Or basically, a function of the signature: (Any -> Boolean) -> (Any -> Boolean)
As @Sylwester suggested, the easiest way to do this is with compose. You could define it as:
(define (invert f)
(compose not f))
Now you could, say, define even? as:
(define even? (invert odd?))
You can also define invert without using compose. I'll give you the template and leave the rest as an exercise:
;; Invert the results of a predicate
;; (Any -> Boolean) -> (Any -> Boolean)
(define (invert f)
(lambda (x)
(cond
[(f x) ...]
[else ...])))
(Note that racket has a shorthand for functions like this:
(define ((invert f) x)
(cond
[(f x) ...]
[else ...]))
answered Nov 25 '18 at 0:35
Leif AndersenLeif Andersen
11.4k135585
It is notinvert. It isnegate.
– PetSerAl
Nov 25 '18 at 10:46
add a comment |
Solution
Write a function, which returns a lambda-expression with applies not to the application of your predicate function on any argument.
(define (my-not predicate-func)
(lambda (x) (not (predicate-func x))))
(my-not f?) returns then a function which is the inverted predicate function of f?.
(So no compose needed ... - well my-not is manually compose-ing the function not with f? (the predicate-function) in its function definition body).
I called it my-not to not to overwrite the already existing not function in Racket which converts booleans thus returns a boolean.
(my-not takes a function and returns a function - Function -> Function or lambda -> lambda :) .)
my-not could be also called invert.
Application
Thus, you can give (my-not f?) to your manual-filter function instead of f?:
(manual-filter (my-not f?) lst)
Try out
You can also test:
(even? 3) ;; #f
(even? 4) ;; #t
((my-not even?) 3) ;; #t
((my-not even?) 4) ;; #f
;; so `(my-not even?)` behaves exactly like `odd?` - the inverse of `even?`
(odd? 3) ;; #t
(odd? 4) ;; #f
answered Nov 25 '18 at 9:59
Gwang-Jin KimGwang-Jin Kim
2,474217
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
the not function has the signature Any -> Boolean. And is essentially:
(define (not x)
(if (eq? x #f) #t #f))
What you are looking for is a function that inverts the output to another given function. (Or basically, a function of the signature: (Any -> Boolean) -> (Any -> Boolean)
As @Sylwester suggested, the easiest way to do this is with compose. You could define it as:
(define (invert f)
(compose not f))
Now you could, say, define even? as:
(define even? (invert odd?))
You can also define invert without using compose. I'll give you the template and leave the rest as an exercise:
;; Invert the results of a predicate
;; (Any -> Boolean) -> (Any -> Boolean)
(define (invert f)
(lambda (x)
(cond
[(f x) ...]
[else ...])))
(Note that racket has a shorthand for functions like this:
(define ((invert f) x)
(cond
[(f x) ...]
[else ...]))
answered Nov 25 '18 at 0:35
Leif AndersenLeif Andersen
11.4k135585
It is notinvert. It isnegate.
– PetSerAl
Nov 25 '18 at 10:46
add a comment |
the not function has the signature Any -> Boolean. And is essentially:
(define (not x)
(if (eq? x #f) #t #f))
What you are looking for is a function that inverts the output to another given function. (Or basically, a function of the signature: (Any -> Boolean) -> (Any -> Boolean)
As @Sylwester suggested, the easiest way to do this is with compose. You could define it as:
(define (invert f)
(compose not f))
Now you could, say, define even? as:
(define even? (invert odd?))
You can also define invert without using compose. I'll give you the template and leave the rest as an exercise:
;; Invert the results of a predicate
;; (Any -> Boolean) -> (Any -> Boolean)
(define (invert f)
(lambda (x)
(cond
[(f x) ...]
[else ...])))
(Note that racket has a shorthand for functions like this:
(define ((invert f) x)
(cond
[(f x) ...]
[else ...]))
answered Nov 25 '18 at 0:35
Leif AndersenLeif Andersen
11.4k135585
It is notinvert. It isnegate.
– PetSerAl
Nov 25 '18 at 10:46
add a comment |
the not function has the signature Any -> Boolean. And is essentially:
(define (not x)
(if (eq? x #f) #t #f))
What you are looking for is a function that inverts the output to another given function. (Or basically, a function of the signature: (Any -> Boolean) -> (Any -> Boolean)
As @Sylwester suggested, the easiest way to do this is with compose. You could define it as:
(define (invert f)
(compose not f))
Now you could, say, define even? as:
(define even? (invert odd?))
You can also define invert without using compose. I'll give you the template and leave the rest as an exercise:
;; Invert the results of a predicate
;; (Any -> Boolean) -> (Any -> Boolean)
(define (invert f)
(lambda (x)
(cond
[(f x) ...]
[else ...])))
(Note that racket has a shorthand for functions like this:
(define ((invert f) x)
(cond
[(f x) ...]
[else ...]))
answered Nov 25 '18 at 0:35
Leif AndersenLeif Andersen
11.4k135585
the not function has the signature Any -> Boolean. And is essentially:
(define (not x)
(if (eq? x #f) #t #f))
What you are looking for is a function that inverts the output to another given function. (Or basically, a function of the signature: (Any -> Boolean) -> (Any -> Boolean)
As @Sylwester suggested, the easiest way to do this is with compose. You could define it as:
(define (invert f)
(compose not f))
Now you could, say, define even? as:
(define even? (invert odd?))
You can also define invert without using compose. I'll give you the template and leave the rest as an exercise:
;; Invert the results of a predicate
;; (Any -> Boolean) -> (Any -> Boolean)
(define (invert f)
(lambda (x)
(cond
[(f x) ...]
[else ...])))
(Note that racket has a shorthand for functions like this:
(define ((invert f) x)
(cond
[(f x) ...]
[else ...]))
answered Nov 25 '18 at 0:35
Leif AndersenLeif Andersen
11.4k135585
answered Nov 25 '18 at 0:35
Leif AndersenLeif Andersen
11.4k135585
answered Nov 25 '18 at 0:35
Leif AndersenLeif Andersen
11.4k135585
answered Nov 25 '18 at 0:35
Leif AndersenLeif Andersen
11.4k135585
11.4k135585
It is notinvert. It isnegate.
– PetSerAl
Nov 25 '18 at 10:46
add a comment |
It is notinvert. It isnegate.
– PetSerAl
Nov 25 '18 at 10:46
It is not
invert. It is negate.– PetSerAl
Nov 25 '18 at 10:46
It is not
invert. It is negate.– PetSerAl
Nov 25 '18 at 10:46
add a comment |
Solution
Write a function, which returns a lambda-expression with applies not to the application of your predicate function on any argument.
(define (my-not predicate-func)
(lambda (x) (not (predicate-func x))))
(my-not f?) returns then a function which is the inverted predicate function of f?.
(So no compose needed ... - well my-not is manually compose-ing the function not with f? (the predicate-function) in its function definition body).
I called it my-not to not to overwrite the already existing not function in Racket which converts booleans thus returns a boolean.
(my-not takes a function and returns a function - Function -> Function or lambda -> lambda :) .)
my-not could be also called invert.
Application
Thus, you can give (my-not f?) to your manual-filter function instead of f?:
(manual-filter (my-not f?) lst)
Try out
You can also test:
(even? 3) ;; #f
(even? 4) ;; #t
((my-not even?) 3) ;; #t
((my-not even?) 4) ;; #f
;; so `(my-not even?)` behaves exactly like `odd?` - the inverse of `even?`
(odd? 3) ;; #t
(odd? 4) ;; #f
answered Nov 25 '18 at 9:59
Gwang-Jin KimGwang-Jin Kim
2,474217
add a comment |
Solution
Write a function, which returns a lambda-expression with applies not to the application of your predicate function on any argument.
(define (my-not predicate-func)
(lambda (x) (not (predicate-func x))))
(my-not f?) returns then a function which is the inverted predicate function of f?.
(So no compose needed ... - well my-not is manually compose-ing the function not with f? (the predicate-function) in its function definition body).
I called it my-not to not to overwrite the already existing not function in Racket which converts booleans thus returns a boolean.
(my-not takes a function and returns a function - Function -> Function or lambda -> lambda :) .)
my-not could be also called invert.
Application
Thus, you can give (my-not f?) to your manual-filter function instead of f?:
(manual-filter (my-not f?) lst)
Try out
You can also test:
(even? 3) ;; #f
(even? 4) ;; #t
((my-not even?) 3) ;; #t
((my-not even?) 4) ;; #f
;; so `(my-not even?)` behaves exactly like `odd?` - the inverse of `even?`
(odd? 3) ;; #t
(odd? 4) ;; #f
answered Nov 25 '18 at 9:59
Gwang-Jin KimGwang-Jin Kim
2,474217
add a comment |
Solution
Write a function, which returns a lambda-expression with applies not to the application of your predicate function on any argument.
(define (my-not predicate-func)
(lambda (x) (not (predicate-func x))))
(my-not f?) returns then a function which is the inverted predicate function of f?.
(So no compose needed ... - well my-not is manually compose-ing the function not with f? (the predicate-function) in its function definition body).
I called it my-not to not to overwrite the already existing not function in Racket which converts booleans thus returns a boolean.
(my-not takes a function and returns a function - Function -> Function or lambda -> lambda :) .)
my-not could be also called invert.
Application
Thus, you can give (my-not f?) to your manual-filter function instead of f?:
(manual-filter (my-not f?) lst)
Try out
You can also test:
(even? 3) ;; #f
(even? 4) ;; #t
((my-not even?) 3) ;; #t
((my-not even?) 4) ;; #f
;; so `(my-not even?)` behaves exactly like `odd?` - the inverse of `even?`
(odd? 3) ;; #t
(odd? 4) ;; #f
answered Nov 25 '18 at 9:59
Gwang-Jin KimGwang-Jin Kim
2,474217
Solution
Write a function, which returns a lambda-expression with applies not to the application of your predicate function on any argument.
(define (my-not predicate-func)
(lambda (x) (not (predicate-func x))))
(my-not f?) returns then a function which is the inverted predicate function of f?.
(So no compose needed ... - well my-not is manually compose-ing the function not with f? (the predicate-function) in its function definition body).
I called it my-not to not to overwrite the already existing not function in Racket which converts booleans thus returns a boolean.
(my-not takes a function and returns a function - Function -> Function or lambda -> lambda :) .)
my-not could be also called invert.
Application
Thus, you can give (my-not f?) to your manual-filter function instead of f?:
(manual-filter (my-not f?) lst)
Try out
You can also test:
(even? 3) ;; #f
(even? 4) ;; #t
((my-not even?) 3) ;; #t
((my-not even?) 4) ;; #f
;; so `(my-not even?)` behaves exactly like `odd?` - the inverse of `even?`
(odd? 3) ;; #t
(odd? 4) ;; #f
answered Nov 25 '18 at 9:59
Gwang-Jin KimGwang-Jin Kim
2,474217
edited Nov 25 '18 at 10:41
answered Nov 25 '18 at 9:59
Gwang-Jin KimGwang-Jin Kim
2,474217
answered Nov 25 '18 at 9:59
Gwang-Jin KimGwang-Jin Kim
2,474217
answered Nov 25 '18 at 9:59
Gwang-Jin KimGwang-Jin Kim
2,474217
2,474217
add a comment |
add a comment |
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(define even? (compose not odd?))?– Sylwester
Nov 25 '18 at 0:22
it's for a homework question so we can't use abstract functions such as compose, and odd? was an example, it could be any predicate
– Syvash
Nov 25 '18 at 0:24