40 lines
963 B
Plaintext
40 lines
963 B
Plaintext
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// Example of using type classes to implement `unwrap`.
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// Types that can be unwrapped.
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class Unwrap a {
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// The result that `unwrap`ping will produce when successfully applied.
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type Result;
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// Unwraps `self` into the result type, panicking on failure.
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def unwrap (self: a) -> Result;
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}
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// Either an `a`, or no data.
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data Option a
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= Some a
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| None;
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// `Option a` can be unwrapped to produce `a`.
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instance Unwrap (Option a) {
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type Result = a;
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def unwrap self = match self {
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Some x -> x,
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None -> panic "Attempt to unwrap None",
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};
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}
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// Either an `a`, or an error of type `e` (which must be representable as a string, hence the `Show`
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// bound).
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data Result a (e: Show)
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= Ok a
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| Err e;
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// `Result a e` can be unwrapped to produce `a`.
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instance Unwrap (Result a e) {
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type Result = a;
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def unwrap self = match self {
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Ok x -> x,
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Err e -> panic ("Attempt to unwrap Err " ++ show e),
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}
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}
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