Documenting expected behaviour of intersection types #13384
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radeusgd
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radeusgd
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AdRiley,
GregoryTravis,
JaroslavTulach and
jdunkerley
GregoryTravis
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Jun 26, 2025
| - inspecting the type via `case of`, e.g. | ||
| ``` | ||
| case x of | ||
| a : A -> ... |
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What happens in this case?
Suggested change
| a : A -> ... | |
| b : B -> ... | |
| a : A -> ... |
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case of patterns do not invoke conversions
| ``` | ||
| in the first branch, the `a` has visible type `A` but the full type is still | ||
| `a : A & (hidden B)` - the `B` part is hidden, but not removed. | ||
| - dispatching a method on one of the types, e.g. calling `x.method_defined_on_A` |
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Is it the same when calling a method defined on a hidden type? x.method_defined_on_B?
| will pass the value `x` as `self` to the body of `method_defined_on_A`, the | ||
| `self` will have a visible type `A`, but the full type is still | ||
| `self : A & (hidden B)` - so the `self` value can be casted if needed. | ||
| - normally, calling conversions will 'start over' and the value returned from |
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What happens if there are conversions from both A and B to some other type? Do unhidden ones take precedence over hidden ones?
JaroslavTulach
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Jun 27, 2025
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- Thanks for improving the docs, Radek.
- I prefer positive tone in the docs
- e.g. describe how great Enso design is
- and only then warn what would happen if it wasn't as great
| the original value. E.g. `4.2 : Complex&Float : Float` is `==` and has the same | ||
| `hash` as `4.2` (in spite it _can be cast to_ `Complex`). | ||
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| ### TODO |
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What's the purpose of this TODO? If the functionality is broken, can we link to the appropriate issues?
self preserves intersection types, just hides them
That works, doesn't it?
docs/types/intersection-types.md
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| its identity as a `Table & DB_Table` and can be uncovered via a cast or a case | ||
| expression. | ||
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| It is important to ensure that various operations do not accidentally remove a |
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- I don't like the term various operations
- it only spreads FUD
- there is no point of being so vague in the documentation
- if you have to, move it into a "warning" or "notice" section
- e.g. a colloquial knowledge, not part of the spec
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