Slicing

This section contains functions to make subsequences from iterators.

Basic

fun.nth(n, gen, param, state)

iterator:nth(n)

Parameters

n (uint) – a sequential number (indexed starting from 1, like Lua tables)

Returns

n-th element of gen, param, state iterator

This function returns the n-th element of gen, param, state iterator. If the iterator does not have n items then nil is returned.

Examples:

> print(nth(2, range(5)))
2

> print(nth(10, range(5)))
nil

> print(nth(2, {"a", "b", "c", "d", "e"}))
b

> print(nth(2, enumerate({"a", "b", "c", "d", "e"})))
2 b

This function is optimized for basic array and string iterators and has O(1) complexity for these cases.

fun.head(gen, param, state)

iterator:head()

Returns

a first element of gen, param, state iterator

Extract the first element of gen, param, state iterator. If the iterator is empty then an error is raised.

Examples:

> print(head({"a", "b", "c", "d", "e"}))
a
> print(head({}))
error: head: iterator is empty
> print(head(range(0)))
error: head: iterator is empty
> print(head(enumerate({"a", "b"})))
1 a

fun.car(gen, param, state)

An alias for head().

fun.tail(gen, param, state)

iterator:tail()

Returns

gen, param, state iterator without a first element

Return a copy of gen, param, state iterator without its first element. If the iterator is empty then an empty iterator is returned.

Examples:

> each(print, tail({"a", "b", "c", "d", "e"}))
b
c
d
e
> each(print, tail({}))
> each(print, tail(range(0)))
> each(print, tail(enumerate({"a", "b", "c"})))
2 b
3 c

fun.cdr(gen, param, state)

An alias for tail().

Subsequences

fun.take_n(n, gen, param, state)

iterator:take_n(n)

Parameters

n (uint) – a number of elements to take

Returns

an iterator on the subsequence of first n elements

Examples:

> each(print, take_n(5, range(10)))
1
2
3
4
5

> each(print, take_n(5, enumerate(duplicate('x'))))
1 x
2 x
3 x
4 x
5 x

fun.take_while(predicate, gen, param, state)

iterator:take_while(predicate)

Returns

an iterator on the longest prefix of gen, param, state elements that satisfy predicate.

Examples:

> each(print, take_while(function(x) return x < 5 end, range(10)))
1
2
3
4

> each(print, take_while(function(i, a) return i ~=a end,
    enumerate({5, 3, 4, 4, 2})))
1       5
2       3
3       4

See also

filter()

fun.take(n_or_predicate, gen, param, state)

iterator:take(n_or_predicate)

An alias for take_n() and take_while() that autodetects required function based on n_or_predicate type.

fun.drop_n(n, gen, param, state)

iterator:drop_n(n)

Parameters

n (uint) – the number of elements to drop

Returns

gen, param, state iterator after skipping first n elements

Examples:

> each(print, drop_n(2, range(5)))
3
4
5

> each(print, drop_n(2, enumerate({'a', 'b', 'c', 'd', 'e'})))
3       c
4       d
5       e

fun.drop_while(predicate, gen, param, state)

iterator:drop_while(predicate)

Returns

gen, param, state after skipping the longest prefix of elements that satisfy predicate.

Examples:

> each(print, drop_while(function(x) return x < 5 end, range(10)))
5
6
7
8
9
10

See also

filter()

fun.drop(n_or_predicate, gen, param, state)

iterator:drop(n_or_predicate)

An alias for drop_n() and drop_while() that autodetects required function based on n_or_predicate type.

fun.span(n_or_predicate, gen, param, state)

iterator:span(n_or_predicate)

Returns

iterator, iterator

Return an iterator pair where the first operates on the longest prefix (possibly empty) of gen, param, state iterator of elements that satisfy predicate and second operates the remainder of gen, param, state iterator. Equivalent to:

return take(n_or_predicate, gen, param, state),
       drop(n_or_predicate, gen, param, state);

Examples:

> each(print, zip(span(function(x) return x < 5 end, range(10))))
1       5
2       6
3       7
4       8

> each(print, zip(span(5, range(10))))
1       6
2       7
3       8
4       9
5       10

Note

gen, param, state must be pure functional to work properly with the function.

See also

partition()

fun.split(n_or_predicate, gen, param, state)

An alias for span().

fun.split_at(n, gen, param, state)

An alias for span().