tuple
元组
元组
tuple 有序
n 元;
n 重序元
tuple n 倍;
n 元组;
n 元数;
n 元向量
tuple 重元组
tuple 元
In {
functional languages },
a data object containing two or
more components .
Also known as a product type or pair ,
triple ,
quad ,
etc .
Tuples of different sizes have different
types ,
in contrast to lists where the type is independent of
the length .
The components of a tuple may be of different
types whereas all elements of a list have the same type .
Examples of tuples in {
Haskell }
notation are (
1 ,
2 ),
("
Tuple ",
True ), (
w ,(
x ,
y ),
z ).
The degenerate tuple with zero
components ,
written (),
is known as the unit type since it has
only one possible value which is also written ().
The implementation of tuples in a language may be either
"{
lifted }"
or not .
If tuples are lifted then (
bottom ,
bottom )
/=
bottom and the evaluation of a tuple may fail to terminate .
E .
g .
in Haskell :
f (
x ,
y ) =
1 -->
f bottom =
bottom
f (
bottom ,
bottom ) =
1
With lifted tuples ,
a tuple pattern is refutable .
Thus in
Haskell , {
pattern matching }
on tuples is the same as pattern
matching on types with multiple constructors ({
algebraic data
types }) -
the expression being matched is evaluated as far as
the top level constructor ,
even though ,
in the case of tuples ,
there is only one possible constructor for a given type .
If tuples are unlifted then (
bottom ,
bottom ) =
bottom and
evaluation of a tuple will never fail to terminate though any
of the components may .
E .
g .
in {
Miranda }:
f (
x ,
y ) =
1 -->
f bottom =
1
f (
bottom ,
bottom ) =
1
Thus in Miranda ,
any object whose type is compatible with a
tuple pattern is assumed to match at the top level without
evaluation -
it is an {
irrefutable }
pattern .
This also
applies to user defined data types with only one constructor .
In Haskell ,
patterns can be made irrefutable by adding a "~"
as in
f ~(
x ,
y ) =
1 .
If tuple constructor functions were {
strict }
in all their
arguments then (
bottom ,
x ) = (
x ,
bottom ) =
bottom for any x so
matching a refutable pattern would fail to terminate if any
component was bottom .
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