 | tagged-0.1.1: Provides newtype wrappers for phantom types to avoid unsafely passing dummy arguments | Contents | Index |
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| Data.Tagged | | Portability | portable | | Stability | experimental | | Maintainer | Edward Kmett <ekmett@gmail.com> |
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| Description |
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| Synopsis |
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| Tagged values
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| newtype Tagged s b |
A Tagged s b value is a value b with an attached phantom type s.
This can be used in place of the more traditional but less safe idiom of
passing in an undefined value with the type, because unlike an (s -> b),
a Tagged s b can't try to use the argument s as a real value.
Moreover, you don't have to rely on the compiler to inline away the extra
argument, because the newtype is free
| | Constructors | |  Instances | |
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| retag :: Tagged s b -> Tagged t b |
Some times you need to change the tag you have lying around.
Idiomatic usage is to make a new combinator for the relationship between the
tags that you want to enforce, and define that combinator using retag.
data Succ n
retagSucc :: Tagged n a -> Tagged (Succ n) a
retagSucc = retag
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| untag :: Tagged s b -> b |
| Alias for unTagged
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| tagSelf :: a -> Tagged a a |
| Tag a value with its own type.
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| untagSelf :: Tagged a a -> a |
| untagSelf is a type-restricted version of untag.
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| asTaggedTypeOf :: s -> Tagged s b -> s |
| asTaggedTypeOf is a type-restricted version of const. It is usually used as an infix operator, and its typing forces its first argument (which is usually overloaded) to have the same type as the tag of the second.
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| Proxy values
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| data Proxy p |
| Constructors | | | Instances | |
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| reproxy :: Proxy s -> Proxy t |
Some times you need to change the tag you have lying around.
Idiomatic usage is to make a new combinator for the relationship
between the tags that you want to enforce, and define that
combinator using retag.
data Succ n
reproxySucc :: Proxy n -> Proxy (Succ n)
reproxySucc = reproxy
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| asProxyTypeOf :: a -> Proxy a -> a |
| asProxyTypeOf is a type-restricted version of const.
It is usually used as an infix operator, and its typing forces its first
argument (which is usually overloaded) to have the same type as the tag
of the second.
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| Conversion
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| proxy :: Tagged s a -> Proxy s -> a |
| Convert from a Tagged representation to a representation
based on a Proxy.
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| unproxy :: (Proxy s -> a) -> Tagged s a |
| Convert from a representation based on a Proxy to a Tagged
representation.
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| Produced by Haddock version 2.7.2 |