Re: [racket-users] Why are hash and make-hash not symmetric?

[David Storrs]

Thank you, Spencer and Matthew both.  That gives me enough to go on with.


On Wed, Dec 7, 2016 at 9:59 AM, Matthew Flatt  wrote:

> Maybe there's some technical reason that I've forgotten, but I think
> it's just that `hash` is newer and was an experiment toward a better
> interface. A `mutable-hash` function would make sense, as far as I can
> tell.
>
> Meanwhile, something like `(hash-copy (hash 'a 1 'b 2))` might be the
> most convenient option right now.
>
> At Wed, 7 Dec 2016 08:49:42 -0800, David Storrs wrote:
> > -> (hash 'a 1 'b 2)
> > '#hash((a . 1) (b . 2))
> >
> > -> (make-hash '((a . 1) (b . 2)))
> > '#hash((b . 2) (a . 1))
> >
> > -> (make-hash 'a 1 'b 2)
> > (make-hash 'a 1 'b 2)
> > ; make-hash: arity mismatch;
> > ;  the expected number of arguments does not match the given number
> > ;   expected: 0 to 1
> > ;   given: 4
> > ; [,bt for context]
> >
> > Why does 'make-hash' not work like 'hash'?  Is it possible that a flag
> > could be added that would *make* it work like hash?  Or, alternatively,
> > does another function exist that will create a mutable hash but will
> accept
> > N arguments the way 'hash' does?  I understand that it's not very FP to
> use
> > mutation but there are certain problems that are easier that way.
>
>

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Re: [racket-users] Why are hash and make-hash not symmetric?

[Matthew Flatt]

Maybe there's some technical reason that I've forgotten, but I think
it's just that `hash` is newer and was an experiment toward a better
interface. A `mutable-hash` function would make sense, as far as I can
tell.

Meanwhile, something like `(hash-copy (hash 'a 1 'b 2))` might be the
most convenient option right now.

At Wed, 7 Dec 2016 08:49:42 -0800, David Storrs wrote:
> -> (hash 'a 1 'b 2)
> '#hash((a . 1) (b . 2))
> 
> -> (make-hash '((a . 1) (b . 2)))
> '#hash((b . 2) (a . 1))
> 
> -> (make-hash 'a 1 'b 2)
> (make-hash 'a 1 'b 2)
> ; make-hash: arity mismatch;
> ;  the expected number of arguments does not match the given number
> ;   expected: 0 to 1
> ;   given: 4
> ; [,bt for context]
> 
> Why does 'make-hash' not work like 'hash'?  Is it possible that a flag
> could be added that would *make* it work like hash?  Or, alternatively,
> does another function exist that will create a mutable hash but will accept
> N arguments the way 'hash' does?  I understand that it's not very FP to use
> mutation but there are certain problems that are easier that way.

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Re: [racket-users] Why are hash and make-hash not symmetric?

[Spencer Florence]

For symmetry there is "make-immutable-hash", which is like "hash" but has
the interface of "make-hash". (I don't know why "hash" is the way it is
though).

--spencer

On Wed, Dec 7, 2016 at 10:49 AM David Storrs  wrote:

> -> (hash 'a 1 'b 2)
> '#hash((a . 1) (b . 2))
>
> -> (make-hash '((a . 1) (b . 2)))
> '#hash((b . 2) (a . 1))
>
> -> (make-hash 'a 1 'b 2)
> (make-hash 'a 1 'b 2)
> ; make-hash: arity mismatch;
> ;  the expected number of arguments does not match the given number
> ;   expected: 0 to 1
> ;   given: 4
> ; [,bt for context]
>
> Why does 'make-hash' not work like 'hash'?  Is it possible that a flag
> could be added that would *make* it work like hash?  Or, alternatively,
> does another function exist that will create a mutable hash but will accept
> N arguments the way 'hash' does?  I understand that it's not very FP to use
> mutation but there are certain problems that are easier that way.
>
> --
> You received this message because you are subscribed to the Google Groups
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>

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[racket-users] Why are hash and make-hash not symmetric?

[David Storrs]

-> (hash 'a 1 'b 2)
'#hash((a . 1) (b . 2))

-> (make-hash '((a . 1) (b . 2)))
'#hash((b . 2) (a . 1))

-> (make-hash 'a 1 'b 2)
(make-hash 'a 1 'b 2)
; make-hash: arity mismatch;
;  the expected number of arguments does not match the given number
;   expected: 0 to 1
;   given: 4
; [,bt for context]

Why does 'make-hash' not work like 'hash'?  Is it possible that a flag
could be added that would *make* it work like hash?  Or, alternatively,
does another function exist that will create a mutable hash but will accept
N arguments the way 'hash' does?  I understand that it's not very FP to use
mutation but there are certain problems that are easier that way.

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