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--- status: Rewritten July 2018
--- author(s): Lily Silverstein
--- notes:
doc ///
Key
prepend
(prepend, Thing, BasicList)
Headline
add an element to the beginning of a list
Usage
prepend(x, L)
Inputs
L:BasicList
x:Thing
Outputs
:BasicList
the list obtained by adding the element {\tt x} to the beginning of list {\tt L}
Description
Example
prepend(3, {1, 7, 8, 3})
L = {"old", "old", "old"};
prepend("new", L)
Text
The new list will be of the same @TO class@ as {\tt L}.
Example
K = (a, b, c);
prepend(z, K)
Text
Only a single element can be prepended with this function. To prepend the elements
of a list, use @TO join@. To add the new element to the end of the list, or
at a particular index, use @TO append@ or @TO insert@, respectively.
Example
join((x, y, z), K)
append(K, z)
insert(1, z, K)
Text
Prepend always returns a {\em new} list, rather than modifying the input list,
even if {\tt L} is a @TO MutableList@.
Example
L = new MutableList from {2,3,5};
peek prepend(7, L)
peek L
Text
Notice that the order of the arguments is switched in {\tt prepend} versus {\tt append}:
we write {\tt prepend(x, L)} and {\tt append(L, x)}. A good way to remember this is
that the new element is visually placed {\em before} or {\em after} the list, depending
on where we want it to appear in the output.
SeeAlso
append
insert
join
"lists and sequences"
///
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