unbinding Binding

[debug-ito]

Sometimes it's useful to have Binding that unbinds some input symbols.

For example,

data Input = A | B | C

bound_A :: Binding s Input
bound_A = binds $ on A `run` putStrLn "hoge"

unbind_A :: Binding s Input
unbind_A = ... -- something that unbind input A

Then,

bound_A  <> unbind_A == mempty
unbind_A <> bound_A  == bound_A

This can be implemented by changing the value type of Binding map from Action ... to Maybe (Action ...). Because Binding and Binder are opaque, the change would be additive (i.e. no need to major version bump).

[debug-ito]

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