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0031542faf
This is for consistency with the `cmark` style. Now the blocks we still pretty-print ourselves will match the bulk of them that `cmark` produces.
121 lines
2.0 KiB
Markdown
121 lines
2.0 KiB
Markdown
This transcript demonstrates that Unison forces actions in blocks to have a return type of `()`.
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This works, as expected:
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``` unison
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structural ability Stream a where emit : a -> ()
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ex1 = do
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Stream.emit 1
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Stream.emit 2
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42
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```
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``` ucm
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Loading changes detected in scratch.u.
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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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structural ability Stream a
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ex1 : '{Stream Nat} Nat
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```
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This does not typecheck, we've accidentally underapplied `Stream.emit`:
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``` unison
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ex2 = do
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Stream.emit
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42
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```
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``` ucm
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Loading changes detected in scratch.u.
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I found a value of type: a ->{Stream a} Unit
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where I expected to find: Unit
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2 | Stream.emit
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3 | 42
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Hint: Actions within a block must have type Unit.
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Use _ = <expr> to ignore a result.
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```
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We can explicitly ignore an unused result like so:
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``` unison
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ex3 = do
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_ = Stream.emit
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()
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```
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``` ucm
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Loading changes detected in scratch.u.
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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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ex3 : '()
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```
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Using a helper function like `void` also works fine:
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``` unison
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void x = ()
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ex4 =
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void [1,2,3]
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()
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```
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``` ucm
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Loading changes detected in scratch.u.
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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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ex4 : ()
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void : x -> ()
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```
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One more example:
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``` unison
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ex4 =
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[1,2,3] -- no good
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()
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```
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``` ucm
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Loading changes detected in scratch.u.
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I found a value of type: [Nat]
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where I expected to find: Unit
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2 | [1,2,3] -- no good
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3 | ()
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from right here:
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2 | [1,2,3] -- no good
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Hint: Actions within a block must have type Unit.
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Use _ = <expr> to ignore a result.
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```
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