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Closes #1547 , which was caused by misspelled/nonexistent types being interpreted as type variables. In #1550 I proposed one solution to the problem, namely, to stop implicitly quantifying types and require explicit `forall` on any polymorphic type. This PR represents an alternative solution: to keep implicit quantification but require all types to start with an uppercase letter, as in Haskell. I think I like this one better but I'm open to feedback. Specifically, with this PR: - All built-in type constructors (`Int`, `Cmd`, `Unit`, etc.) must start with a capital letter - Type variables: - Must start with a lowercase letter or underscore - May not be named a lowercase version of a type constructor, *e.g.* `int` - This is important so that old code with lowercase types is not silently accepted by parsing the former types as implicitly quantified type variables; even in cases where old code no longer typechecks, this will give better error messages. - Term variables: - May start with upper- or lowercase - May be named lowercase versions of type names, *e.g.* `let f : Int -> Int = \int. int + 1` is fine This PR obviously represents a bigger breaking change. Once we merge this we might consider adding an option to `swarm format` to be able to parse old code with lowercase types and then reformat it with uppercase, to aid in porting code. Once this is merged I will also regenerate the wiki pages that mention types. Closes #1550.
21 lines
624 B
Plaintext
21 lines
624 B
Plaintext
// Proof of concept illustrating the possibility of key
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// handlers that process multi-key sequences.
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def cons : a * b -> (a -> b) -> (a -> b) = \p. \k. \a.
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if (a == fst p) {snd p} {k a}
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end
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def nil : a -> Cmd Unit = \a. return () end
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// The delay around the first argument is necessary to prevent
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// infinite recursion
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def handlerB : {Key -> Cmd Unit} -> Key -> Cmd Unit = \hA. \k.
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cons (key "b", move) nil k;
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installKeyHandler "" (force hA)
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end
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// Typing 'a' then 'b' in sequence will cause the robot to move.
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def handlerA : Key -> Cmd Unit =
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cons (key "a", installKeyHandler "" (handlerB {handlerA})) nil
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end
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