Name Rascal/Expressions/Values/ListRelation

Synopsis ListRelation values.

Syntax [ <Exp11, Exp12, ... > , <Exp21, Exp22, ... > , ... ]

Types

Exp11	Exp12	...	{ <Exp11, Exp12, ... > , ... }
T1	T2	...	lrel[T1, T2, ... ]

Usage import ListRelation; (included in Prelude)

Details CartesianProduct Composition FieldSelection Join ReflexiveTransitiveClosure Subscription TransitiveClosure

Description A list relation is a list of elements with the following property:

• All elements have the same static tuple type.

ListRelations are thus nothing more than lists of tuples, but since they are used so often we provide a shorthand notation for them. ListRelations are represented by the type lrel[T1 L1, T2 L2, ... ], where T1, T2, ... are arbitrary types and L1, L2, ... are optional labels. It is a shorthand for list[tuple[T1 L1, T2 L2, ... ]].

An n-ary list relation with m tuples is denoted by [<E11, E12, ..., E1n>,<E21, E22, ..., E2n>, ..., <Em1, Em2, ..., Emn>], where the Eij are expressions that yield the desired element type Ti.

Since list relations are a form of list all operations (see List) and functions (see Prelude/List) are also applicable to relations.

The following additional operators are provided for list relations:

• CartesianProduct: Cartesian product of two list relation values.
• Composition: Composition of two list relation values.
• FieldSelection: Select a field (column) from a list relation value.
• Join: Join two list relation values.
• ReflexiveTransitiveClosure: The reflexive transitive closure of a binary list relation.
• Subscription: Indexing of a list relation via tuple values.
• TransitiveClosure: Transitive closure on binary list relation values.

The following additional functions are provided on list relations:

• carrier: Return the set of all elements in any tuple in a list relation.
• carrierR: A list relation restricted to certain element values in tuples.
• carrierX: A list relation excluding tuples that contain certain element values.
• complement: Complement of a list relation.
• domain: Domain of a list relation: a list consisting of the first element of each tuple.
• domainR: List relation restricted to certain domain elements.
• domainX: List relation excluding certain domain values.
• groupDomainByRange: Make sets of elements in the domain that relate to the same element in the range.
• groupRangeByDomain: Make sets of elements in the range that relate to the same element in the domain.
• ident: The identity list relation.
• index: Listes a binary list relation as a map
• invert: Invert the tuples in a list relation.
• range: The range (i.e., all but the first element of each tuple) of a list relation.
• rangeR: List relation restricted to certain range values.
• rangeX: List relation excluding certain range values.

Examples

rascal>[<1,10>, <2,20>, <3,30>]
lrel[int,int]: [
  <1,10>,
  <2,20>,
  <3,30>
]

instead of lrel[int,int] we can also give list[tuple[int,int]] as type of the above expression remember that these types are interchangeable.

rascal>[<"a",10>, <"b",20>, <"c",30>]
lrel[str,int]: [
  <"a",10>,
  <"b",20>,
  <"c",30>
]
rascal>[<"a", 1, "b">, <"c", 2, "d">]
lrel[str,int,str]: [
  <"a",1,"b">,
  <"c",2,"d">
]

Questions

[Edit] | [New Subconcept] | [Recompile Course] | [Warnings]