HList- Heterogeneous lists

Safe HaskellNone



The HList library

(C) 2004, Oleg Kiselyov, Ralf Laemmel, Keean Schupke

Declarations for various classes and functions that apply for the whole range of heterogeneous collections (HList, TIP, records, etc).



class HExtend e l whereSource

Associated Types

type HExtendR e l Source


(.*.) :: e -> l -> HExtendR e lSource


HExtend e (HList l) 
(HOccursNot * [*] e l, HTypeIndexed l) => HExtend e (TIP l) 
HRLabelSet (: * (Tagged k l v) r) => HExtend (Tagged k l v) (Record r) 

class SubType l l' Source


(HOccurs e (TIP l1), SubType * * (TIP l1) (TIP l2)) => SubType * * (TIP l1) (TIP (: * e l2)) 
SubType * * (TIP l) (TIP ([] *))

Subtyping for TIPs

H2ProjectByLabels k (RecordLabels k r2) r1 r2 rout => SubType * * (Record r1) (Record r2)

Subtyping for records

class HAppend l1 l2 whereSource


hAppend :: l1 -> l2 -> HAppendR l1 l2Source


HAppend (HList l1) (HList l2) 
(HAppend (HList l) (HList l'), HTypeIndexed (HAppendList * l l')) => HAppend (TIP l) (TIP l') 
(HRLabelSet (HAppendList * r1 r2), HAppend (HList r1) (HList r2)) => HAppend (Record r1) (Record r2)
Add a field to a record. Analagous to (++) for lists.
 record .*. field1
        .*. field2

type family HAppendR l1 l2 :: kSource

poly-kinded, but hAppend only works in cases where the kind variable k is *

class HOccurs e l whereSource


hOccurs :: l -> eSource


(HOccurrence e (: * x y) l', HOccurs' e l') => HOccurs e (HList (: * x y)) 
HOccurs e (HList (: * x (: * y l))) => HOccurs e (TIP (: * x (: * y l))) 
~ * e' e => HOccurs e' (TIP (: * e ([] *)))

One occurrence and nothing is left

This variation provides an extra feature for singleton lists. That is, the result type is unified with the element in the list. Hence the explicit provision of a result type can be omitted.

class HOccursNot e l Source


HOccursNot k [*] e l => HOccursNot k * e (TIP l) 
HOccursNot k [*] e ([] *) 
(HEq * e e1 b, HOccursNot' * b e l) => HOccursNot * [*] e (: * e1 l) 

class HProject l l' whereSource


hProject :: l -> l'Source


(HOccurs e l, HProject l (HList l')) => HProject l (HList (: * e l')) 
HProject (HList l) (HList ([] *)) 

class HType2HNat e l n | e l -> nSource

Map a type (key) to a natural (index) within the collection This is a purely type-level computation


(HEq * e1 e b, HType2HNatCase b e1 l n) => HType2HNat * [*] e1 (: * e l) n

Map a type to a natural (index within the collection) This is a purely type-level computation

class HTypes2HNats es l ns | es l -> nsSource


HTypes2HNats [*] [*] ([] *) l ([] HNat)

And lift to the list of types

(HType2HNat k [*] e l n, HTypes2HNats [k] [*] es l ns) => HTypes2HNats [k] [*] (: k e es) l (: HNat n ns) 

class HDeleteMany e l l' | e l -> l' whereSource

Delete all elements with the type-level key e from the collection l. Since the key is type-level, it is represented by a Proxy. (polykinded)


hDeleteMany :: Proxy e -> l -> l'Source


(HEq * e1 e b, HDeleteManyCase * b e1 e l l1) => HDeleteMany * e1 (HList (: * e l)) (HList l1) 
HDeleteMany k e (HList ([] *)) (HList ([] *))