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120 lines
2.4 KiB
Markdown
120 lines
2.4 KiB
Markdown
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```unison
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ability X t where
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x : t -> a -> a
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ability Abort where
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abort : a
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```
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```ucm
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I found and typechecked these definitions in scratch.u. If you
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do an `add` or `update`, here's how your codebase would
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change:
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⍟ These new definitions are ok to `add`:
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ability Abort
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ability X t
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```
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```ucm
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.> add
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⍟ I've added these definitions:
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ability Abort
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ability X t
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```
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This code should not type check. The match on X.x ought to introduce a
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skolem variable `a` such that `c : a` and the continuation has type
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`a ->{X} b`. Thus, `handle c with h : Optional a`, which is not the
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correct result type.
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```unison
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h0 : Request {X t} b -> Optional b
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h0 req = match req with
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{ X.x _ c -> _ } -> handle c with h0
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{ d } -> Some d
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```
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```ucm
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I found a value of type builtin.Optional a1 where I expected to find one of type builtin.Optional a:
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1 | h0 : Request {X t} b -> Optional b
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2 | h0 req = match req with
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3 | { X.x _ c -> _ } -> handle c with h0
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from right here:
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1 | h0 : Request {X t} b -> Optional b
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```
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This code should not check because `t` does not match `b`.
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```unison
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h1 : Request {X t} b -> Optional b
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h1 req = match req with
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{ X.x t _ -> _ } -> handle t with h1
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{ d } -> Some d
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```
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```ucm
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Each case of a match / with expression need to have the same
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type. Here, one is builtin.Optional t and another is
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builtin.Optional b :
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3 | { X.x t _ -> _ } -> handle t with h1
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4 | { d } -> Some d
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from right here:
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1 | h1 : Request {X t} b -> Optional b
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```
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This code should not check for reasons similar to the first example,
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but with the continuation rather than a parameter.
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```unison
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h2 : Request {Abort} r -> r
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h2 req = match req with
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{ Abort.abort -> k } -> handle k 5 with h2
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{ r } -> r
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```
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```ucm
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The 1st argument to the function k is builtin.Nat, but I was expecting a:
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3 | { Abort.abort -> k } -> handle k 5 with h2
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```
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This should work fine.
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```unison
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h3 : Request {X b, Abort} b -> Optional b
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h3 = cases
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{ r } -> Some r
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{ Abort.abort -> _ } -> None
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{ X.x b _ -> _ } -> Some b
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```
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```ucm
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I found and typechecked these definitions in scratch.u. If you
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do an `add` or `update`, here's how your codebase would
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change:
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⍟ These new definitions are ok to `add`:
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h3 : Request {X b, Abort} b -> Optional b
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```
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