A type which behaves similarly to Record, except all elements must fit in the same UArray. A consequence of this is that RecordU has the following properties:

• it is strict in the element types
• it cannot do type-changing updates of RecordU, except if the function applies to all elements
• it probably is slower to update the very first elements of the RecordU

The benefit is that lookups should be faster and records should take up less space. However benchmarks done with a slow HNat2Integral do not suggest that RecordU is faster than Record.

RecordUS is stored as a HList of RecordU to allow the RecordUS to contain elements of different types, so long all of the types can be put into an unboxed array (UArray).

It is advantageous (at least space-wise) to sort the record to keep elements with the same types elements adjacent. See SortForRecordUS for more details.

Reorders a Record such that the RecordUS made from it takes up less space

Bad has alternating Double and Int fields

>>> bad
Record{x=1.0,i=2,y=3.0,j=4}

4 arrays containing one element each are needed when this Record is stored as a RecordUS

>>> recordToRecordUS bad
RecordUS H[RecordU (array (0,0) [(0,1.0)]),RecordU (array (0,0) [(0,2)]),RecordU (array (0,0) [(0,3.0)]),RecordU (array (0,0) [(0,4)])]

It is possible to sort the record

>>> sortForRecordUS bad
Record{x=1.0,y=3.0,i=2,j=4}

This allows the same content to be stored in two unboxed arrays

>>> recordToRecordUS (sortForRecordUS bad)
RecordUS H[RecordU (array (0,1) [(0,1.0),(1,3.0)]),RecordU (array (0,1) [(0,2),(1,4)])]

analogous flip //. Similar to .<++., except it is restricted to cases where the left argument holds a subset of elements.

hMap specialized to RecordU

behaves like map HFind

connect the unpacked x representation with the corresponding list of RecordU u representation.

HSubtract a b is Left (a-b), Right (b-a) or Right HZero

proof that hMap UnboxF :: r xs -> r us can determine xs from us and us from xs

all elements of the list have the same type

quick sort with a special case for sorted lists

the "standard" <= for types. Reuses HEqBy

Note that ghc-7.6 is missing instances for Symbol and Nat, so that sorting only works HNat (as used by Data.HList.Label3).

analogous to Down

Provided the labels involved have an appropriate instance of HEqByFn, it would be possible to use the following definitions:

type HRLabelSet = HSet
type HLabelSet  = HSet

>>> let xx = Proxy :: HIsSet [Label "x", Label "x"] b => Proxy b
>>> :t xx
xx :: Proxy 'False

>>> let xy = Proxy :: HIsSet [Label "x", Label "y"] b => Proxy b
>>> :t xy
xy :: Proxy 'True

HAscList le xs confirms that xs is in ascending order, and reports which element is duplicated otherwise.

HIsAscList le xs b is analogous to

b = all (\(x,y) -> x `le` y) (xs `zip` tail xs)

'curry'/'uncurry' for many arguments and HLists instead of tuples

XXX the last FD xs -> n is needed to make hCompose infer the right types: arguably it shouldn't be needed

Note: with ghc-7.10 the Arity constraint added here does not work properly with hCompose, so it is possible that other uses of hCurry are better served by hCurry' Proxy.

compose two functions that take multiple arguments. The result of the second function is the first argument to the first function. An example is probably clearer:

>>> let f = hCompose (,,) (,)
>>> :t f
f :: ... -> ... -> ... -> ... -> ((..., ...), ..., ...)

>>> f 1 2 3 4
((1,2),3,4)

Note: polymorphism can make it confusing as to how many parameters a function actually takes. For example, the first two ids are id :: (a -> b) -> (a -> b) in

>>> (.) id id id 'y'
'y'

>>> hCompose id id id 'y'
'y'

still typechecks, but in that case hCompose i1 i2 i3 x == i1 ((i2 i3) x) has id with different types than @(.) i1 i2 i3 x == (i1 (i2 i3)) x

Prompted by http://stackoverflow.com/questions/28932054/can-hlistelim-be-composed-with-another-function

TIPs are like Record, except element "i" of the list "l" has type Tagged e_i e_i

provides a Lens (TIP s) (TIP t) a b

When using set (also known as .~), tipyLens' can address the ambiguity as to which field "a" should actually be updated.

provides a Lens' (TIP s) a. hLens' :: Label a -> Lens' (TIP s) a is another option.

Use Labels to specify the first argument

The same as tipyProject, except also return the types not requested in the proxy argument

project a TIP (or HList) into a tuple

tipyTuple' x = (hOccurs x, hOccurs x)

behaves similarly, except tipyTuple excludes the possibility of looking up the same element twice, which allows inferring a concrete type in more situations. For example

(\x y z -> tipyTuple (x .*. y .*. emptyTIP) `asTypeOf` (x, z)) () 'x'

has type Char -> ((), Char). tipyTuple' would need a type annotation to decide whether the type should be Char -> ((), Char) or () -> ((), ())

TagR can also be used to avoid redundancy when defining types for TIC and TIP.

 type XShort = TagR [A,B,C,D]

 type XLong = [Tagged A A, Tagged B B, Tagged C C, Tagged D D]

an equivalent FD version, which is slightly better with respect to simplifying types containing type variables (in ghc-7.8 and 7.6): http://stackoverflow.com/questions/24110410/

With ghc-7.10 (http://ghc.haskell.org/trac/ghc/ticket/10009) the FD version is superior to the TF version:

class (UntagR (TagR a) ~ a) => TagUntag a where
    type TagR a :: [*]
    hTagSelf :: HList a -> HList (TagR a)
    hUntagSelf :: HList (TagR a) -> HList a

instance TagUntag '[] where
    type TagR '[] = '[]
    hTagSelf _ = HNil
    hUntagSelf _ = HNil

instance TagUntag xs => TagUntag (x ': xs) where
    type TagR (x ': xs) = Tagged x x ': TagR xs
    hTagSelf (HCons x xs) = Tagged x HCons hTagSelf xs
    hUntagSelf (HCons (Tagged x) xs) = x HCons hUntagSelf xs

type family UntagR (xs :: [*]) :: [*]
type instance UntagR '[] = '[]
type instance UntagR (x ': xs) = Untag1 x ': UntagR xs

Length information should flow backwards

>>> let len2 x = x `asTypeOf` (undefined :: HList '[a,b])
>>> let f = len2 $ hTagSelf (hReplicate Proxy ())
>>> :t f
f :: HList '[Tagged () (), Tagged () ()]

Transforming a TIP: applying to a TIP a (polyvariadic) function that takes arguments from a TIP and updates the TIP with the result.

In more detail: we have a typed-indexed collection TIP and we would like to apply a transformation function to it, whose argument types and the result type are all in the TIP. The function should locate its arguments based on their types, and update the TIP with the result. The function may have any number of arguments, including zero; the order of arguments should not matter.

The problem was posed by Andrew U. Frank on Haskell-Cafe, Sep 10, 2009. http://www.haskell.org/pipermail/haskell-cafe/2009-September/066217.html The problem is an interesting variation of the keyword argument problem.

Examples can be found in examples/TIPTransform.hs and examples/TIPTransformM.hs

In March 2010, Andrew Frank extended the problem for monadic operations. This is the monadic version of TIPTransform.hs in the present directory.

This is the TF implementation. When specifying the operation to perform over a TIP, we can leave it polymorphic over the monad. The type checker will instantiate the monad based on the context.

A datatype for type-indexed co-products. A TIC is just a Variant, where the elements of the type-level list "l" are in the form Tagged x x.

make a TIC for use in contexts where the result type is fixed

make a TIC that contains one element

Public constructor (or, open union's injection function)

Prism' (TIC s) a

Variant vs has an implementation similar to Dynamic, except the contained value is one of the elements of the vs list, rather than being one particular instance of Typeable.

>>> v .!. _right
Nothing

>>> v .!. _left
Just 'x'

In some cases the pun quasiquote works with variants,

>>> let f [pun| left right |] = (left,right)
>>> f v
(Just 'x',Nothing)

>>> f w
(Nothing,Just 5)

>>> let add1 v = hMapV (Fun succ :: Fun '[Enum] '()) v

>>> f (add1 v)
(Just 'y',Nothing)

>>> f (add1 w)
(Nothing,Just 6)

in ghc>=7.8, coerce is probably a better choice

Apply a function to all possible elements of the variant

shortcut for applyAB . HMapV. hMap is more general

hMapOutV f = unvariant . hMapV f, except an ambiguous type variable is resolved by HMapOutV_gety

Applies to variants that have the same labels in the same order. A generalization of

zipEither :: Either a b -> Either a b -> Maybe (Either (a,a) (b,b))
zipEither (Left a) (Left a') = Just (Left (a,a'))
zipEither (Right a) (Right a') = Just (Right (a,a'))
zipEither _ _ = Nothing

see HZip for zipping other collections

Apply a record of functions to a variant of values. The functions are selected based on those having the same label as the value.

>>> let xy = x .*. y .*. emptyProxy
>>> let p = Proxy `asLabelsOf` xy
>>> let vs = [ mkVariant x 1.0 p, mkVariant y () p ]

>>> zipVR (hBuild (+1) id) `map` vs
[V{x=2.0},V{y=()}]

convert a variant with more fields into one with fewer (or the same) fields.

>>> let ty = Proxy :: Proxy [Tagged "left" Int, Tagged "right" Int]
>>> let l = mkVariant _left 1 ty
>>> let r = mkVariant _right 2 ty

>>> map projectVariant [l, r] :: [Maybe (Variant '[Tagged "left" Int])]
[Just V{left=1},Nothing]

rearrangeVariant = fromJust . projectVariant is one implementation of rearrangeVariant, since the result can have the same fields with a different order:

>>> let yt = Proxy :: Proxy [Tagged "right" Int, Tagged "left" Int]

>>> map projectVariant [l, r] `asTypeOf` [Just (mkVariant _left 0 yt)]
[Just V{left=1},Just V{right=2}]

projectVariant . extendsVariant = Just (when the types match up)

extendVariant is a special case

projectExtendVariant = fmap extendVariant . projectVariant

where intermediate variant is as large as possible. Used to implement Data.HList.Labelable.projected

Note that:

>>> let r = projectExtendVariant (mkVariant1 Label 1 :: Variant '[Tagged "x" Int])
>>> r :: Maybe (Variant '[Tagged "x" Integer])
Nothing

Make a Prism (Variant s) (Variant t) a b out of a Label.

See Data.HList.Labelable.hLens' is a more overloaded version.

Few type annotations are necessary because of the restriction that s and t have the same labels in the same order, and to get "t" the "a" in "s" is replaced with "b".

Lens (Variant s) (Variant t) a b

Analogue of Control.Lens.chosen :: Lens (Either a a) (Either b b) a b

Lens' (Variant s) a

where we might have s ~ '[Tagged t1 a, Tagged t2 a]

x ~ Tagged s t

Convert a Variant which has all possibilities having the same type into a value of that type. Analogous to either id id.

See also unvariant'

Similar to unvariant, except type variables in v will be made equal to e if possible. That allows the type of Nothing to be inferred as Maybe Char.

>>> unvariant' $ x .=. Nothing .*. mkVariant1 y 'y'
'y'

However, this difference leads to more local error messages (Couldn't match type ‘()’ with ‘Char’), rather than the following with unvariant:

Fail
   '("Variant",
     '[Tagged "left" Char, Tagged "right" ()],
     "must have all values equal to ",
     e))

Conversion between type indexed collections (TIC and TIP) and the corresponding collection that has other label types (Variant and Record respectively)

See typeIndexed'

Iso' (Variant s) (TIC a)

Iso' (Record s) (TIP a)

where s has a type like '[Tagged "x" Int], and a has a type like '[Tagged Int Int].

Iso (TIP (TagR a)) (TIP (TagR b)) (HList a) (HList b)

Iso' (TIP (TagR s)) (HList a)

Iso (Record x) (Record y) (RecordU x) (RecordU y)

Iso' (Record x) (RecordU x)

Iso (Record x) (Record y) (RecordUS x) (RecordUS y)

Iso' (Record x) (RecordUS x)

Prism (Record tma) (Record tmb) (Variant ta) (Variant tb)

see hMaybied'

Prism' (Record tma) (Variant ta)

where tma and tmb are lists like

tma ~ '[Tagged x (Maybe a), Tagged y (Maybe b)]
ta  ~ '[Tagged x        a , Tagged y        b ]

If one element of the record is Just, the Variant will contain that element. Otherwise, the prism fails.

Note

The types work out to define a prism:

l = prism' variantToHMaybied (listToMaybe . hMaybiedToVariants)

but the law: s^?l ≡ Just a ==> l # a ≡ s is not followed, because we could have:

  s, s2 :: Record '[Tagged "x" (Maybe Int), Tagged "y" (Maybe Char)]
  s = hBuild (Just 1) (Just '2')
  s2 = hBuild (Just 1) Nothing

  v :: Variant '[Tagged "x" Int, Tagged "y" Char]
  v = mkVariant (Label :: Label "x") 1 Proxy

So that s^?l == Just v. But l#v == s2 /= s, while the law requires l#v == s. hMaybied avoids this problem by only producing a value when there is only one present.

Iso (TIC s) (TIC t) (Variant s) (Variant t)

typeIndexed may be more appropriate

Iso' (TIC s) (Variant s)

Iso (TIP s) (TIP t) (Record s) (Record t)

typeIndexed may be more appropriate

Iso' (TIP (TagR s)) (Record a)

Every element of the record that is Just becomes one element in the resulting list. See hMaybied' example types that r and v can take.

kw takes a HList whose first element is a function, and the rest of the elements are default values. A useful trick is to have a final argument () which is not eaten up by a label (A only takes 1 argument). That way when you supply the () it knows there are no more arguments (?).

>>> data A = A
>>> instance IsKeyFN (A -> a -> b) True
>>> let f A a () = a + 1
>>> let f' = f .*. A .*. 1 .*. HNil

>>> kw f' A 0 ()
1

>>> kw f' ()
2

convert a Record into a list that can supply default arguments for kw

A bit of setup:

>>> :set -XQuasiQuotes
>>> import Data.HList.RecordPuns
>>> let f (_ :: Label "a") a (_ :: Label "b") b () = a `div` b

>>> let a = 2; b = 1; f' = f .*. recToKW [pun| a b |]
>>> kw f' ()
2

>>> kw f' (Label :: Label "a") 10 ()
10

All our keywords must be registered