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| author | Ben Gamari <bgamari.foss@gmail.com> | 2017-09-13 12:23:47 -0400 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2017-09-13 16:45:49 -0400 |
| commit | f9bf621caf2fc17d829dee0ee48b204144927e72 (patch) | |
| tree | 2cd9ffe866fdfe6a25dcf090fa21c5f7a74b5d2c | |
| parent | 2fe6f6baba70de071c391bccc77197ab4f81064d (diff) | |
| download | haskell-f9bf621caf2fc17d829dee0ee48b204144927e72.tar.gz | |
Better document TypeRep patterns
As pointed out in #14199 these are rather non-trivial; extra
documentation is in order.
[skip ci]
Test Plan: Read it
Reviewers: dfeuer, austin, hvr
Subscribers: rwbarton, thomie
GHC Trac Issues: #14199
Differential Revision: https://phabricator.haskell.org/D3943
| -rw-r--r-- | libraries/base/Data/Typeable/Internal.hs | 28 |
1 files changed, 27 insertions, 1 deletions
diff --git a/libraries/base/Data/Typeable/Internal.hs b/libraries/base/Data/Typeable/Internal.hs index cf3ea0732d..f094d96c02 100644 --- a/libraries/base/Data/Typeable/Internal.hs +++ b/libraries/base/Data/Typeable/Internal.hs @@ -221,6 +221,13 @@ instance Ord SomeTypeRep where SomeTypeRep a `compare` SomeTypeRep b = typeRepFingerprint a `compare` typeRepFingerprint b +-- | The function type constructor. +-- +-- For instance, +-- @ +-- typeRep \@(Int -> Char) === Fun (typeRep \@Int) (typeRep \@Char) +-- @ +-- pattern Fun :: forall k (fun :: k). () => forall (r1 :: RuntimeRep) (r2 :: RuntimeRep) (arg :: TYPE r1) (res :: TYPE r2). @@ -265,7 +272,14 @@ mkTrApp a b = TrApp fpr a b fpr_b = typeRepFingerprint b fpr = fingerprintFingerprints [fpr_a, fpr_b] --- | Pattern match on a type application +-- | A type application. +-- +-- For instance, +-- @ +-- typeRep \@(Maybe Int) === App (typeRep \@Maybe) (typeRep \@Int) +-- @ +-- Note that this will never match a function type (e.g. @Int -> Char@). +-- pattern App :: forall k2 (t :: k2). () => forall k1 (a :: k1 -> k2) (b :: k1). (t ~ a b) => TypeRep a -> TypeRep b -> TypeRep t @@ -287,6 +301,18 @@ pattern Con con <- TrTyCon _ con _ -- | Pattern match on a type constructor including its instantiated kind -- variables. +-- +-- For instance, +-- @ +-- App (Con' proxyTyCon ks) intRep = typeRep @(Proxy \@Int) +-- @ +-- will bring into scope, +-- @ +-- proxyTyCon :: TyCon +-- ks == [someTypeRep @Type] :: [SomeTypeRep] +-- intRep == typeRep @Int +-- @ +-- pattern Con' :: forall k (a :: k). TyCon -> [SomeTypeRep] -> TypeRep a pattern Con' con ks <- TrTyCon _ con ks |