assoc-lens not working with set

[jnboehm]

Using lens-set with assoc-lens does not work in case the key is not present.

> (lens-set (assoc-lens 'a) '((b 1)) 123)
'((b 1))

Using the dict-ref-lens does in fact set the key properly.

> (lens-set (dict-ref-lens 'a) '((b 1)) 123)
'((b 1) (a . 123))

To me this seems like a bug or is this intentional?

[jackfirth]

It's for the same reason as hash-ref-lens, mentioned here. Although it probably should have thrown an error instead of doing nothing. The dict-ref case is similar: it should be throwing an error there too.

[jnboehm]

Thanks for the feedback. Although the example works for a hash-map. I only want to set a key, so there is no need to lens-view a value before. I'm a bit surprised that there is such an inconsistency.

> (lens-set (hash-ref-lens 'a) (hash) "bla")
'#hash((a . "bla"))

But the equivalent with an assoc does not. Hence my confusion. I'm never viewing any non-existing data, so I would have expected the initial example to work.