partial.lenses - npm Package Versions

14.0.0

The current plan is to change Partial Lenses to support so called naked or prototypeless objects with null prototype (i.e. Object.create(null)) in a following major version. This is a breaking change although it is likely that it will not affect most users. Usefully warning for this change of behaviour by adding diagnostics to optics seems somewhat difficult.

Previously obsoleted L.iftes was removed.

The L.Constant functor was removed. It can be replaced as follows:

-L.constant
+{map: (_, x) => x}

L.get has been changed to use the now exported L.Select applicative instead of the removed L.Constant functor. The reason for this change is that it both generalizes L.get and simplifies things overall.

L.get now works exactly like L.select. L.select and L.selectAs have been consequently obsoleted. Change usages as follows:

-L.select(...)
+L.get(...)

-L.selectAs(...)
+L.getAs(...)

In the cases where L.get previously returned a valid result, the only differences are in the cases where L.zero is involved. L.zero is used by several other combinators that could be used as lenses including the conditionals,

• L.cond, and
• L.condOf,

and the querying combinators,

• L.chain,
• L.choice,
• L.optional,
• L.unless, and
• L.when,

and the transform ops,

• L.assignOp,
• L.modifyOp,
• L.removeOp, and
• L.setOp.

Previously L.zero was implemented so that it did something reasonable even with a plain functor. Since no operation in this library now uses a plain functor, the special case behaviour of L.zero has been removed. When previously used with L.get, L.zero passed undefined to the inner optics and ignored what the inner optics returned. For example, previously:

L.get(['x', L.when(x => x > 0), L.valueOr(0)], {x: -1})
// 0

but now L.zero exits early:

L.get(['x', L.when(x => x > 0), L.valueOr(0)], {x: -1})
// undefined

This is clearly a breaking change. However, this is unlikely to affect a large number of use cases. To get the old behavior, use of L.zero needs to be avoided. In the example case, one could write:

L.get(['x', L.ifElse(x => x > 0, [], R.always(0))], {x: -1})
// 0