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iterator

all

|Iterable, test: |Any| -> Bool| -> Bool

Checks the Iterable's values against a test function.

The test function should return true if the value passes the test, otherwise it should return false.

all will return true if all values pass the test, otherwise it will return false.

all stops running as soon as it finds a value that fails the test.

Example

print! (1..9).all |x| x > 0
check! true

print! ('', '', 'foo').all string.is_empty
check! false

print! [10, 20, 30]
  .each |x| x / 10
  .all |x| x < 10
check! true

See Also

any

|Iterable, test: |Any| -> Bool| -> Bool

Checks the Iterable's values against a test function.

The test function should return true if the value passes the test, otherwise it should return false.

any will return true if any of the values pass the test, otherwise it will return false.

any stops running as soon as it finds a passing test.

Example

print! (1..9).any |x| x == 5
check! true

print! ('', '', 'foo').any string.is_empty
check! true

print! [10, 20, 30]
  .each |x| x / 10
  .any |x| x == 2
check! true

See Also

chain

|first: Iterable, second: Iterable| -> Iterator

chain returns an iterator that iterates over the output of the first iterator, followed by the output of the second iterator.

Example

print! [1, 2]
  .chain 'abc'
  .to_tuple()
check! (1, 2, 'a', 'b', 'c')

chunks

|Iterable, size: Number| -> Iterator

Returns an iterator that splits up the input data into chunks of size N, where each chunk is provided as a Tuple. The final chunk may have fewer than N elements.

Example

print! 1..=10
  .chunks 3
  .to_list()
check! [(1, 2, 3), (4, 5, 6), (7, 8, 9), (10)]

consume

|Iterable| -> Null

Consumes the output of the iterator.

|Iterable, |Any| -> Any| -> Null

Consumes the output of the iterator, calling the provided function with each iterator output value.

Example

result = []
1..=10
  .keep |n| n % 2 == 0
  .each |n| result.push n
  .consume()
print! result
check! [2, 4, 6, 8, 10]

# Alternatively, calling consume with a function is equivalent to having an
# `each` / `consume` chain
result = []
1..=10
  .keep |n| n % 2 == 1
  .consume |n| result.push n
print! result
check! [1, 3, 5, 7, 9]

count

|Iterable| -> Number

Counts the number of items yielded from the iterator.

Example

print! (5..15).count()
check! 10

print! 0..100
  .keep |x| x % 2 == 0
  .count()
check! 50

cycle

|Iterable| -> Iterator

Takes an Iterable and returns a new iterator that endlessly repeats the iterable's output.

The iterable's output gets cached, which may result in a large amount of memory being used if the cycle has a long length.

Example

print! (1, 2, 3)
  .cycle()
  .take 10
  .to_list()
check! [1, 2, 3, 1, 2, 3, 1, 2, 3, 1]

each

|Iterable, function: |Any| -> Any| -> Iterator

Creates a new iterator that yields the result of calling the provided function with each value from the input iterator.

Example

print! (2, 3, 4)
  .each |x| x * 2
  .to_list()
check! [4, 6, 8]

enumerate

|Iterable| -> Iterator

Creates an iterator that yields each value along with an associated index.

Example

print! ('a', 'b', 'c').enumerate().to_list()
check! [(0, 'a'), (1, 'b'), (2, 'c')]

find

|Iterable, test: |Any| -> Bool| -> Any

Returns the first value in the iterable that passes the test function.

The function is called for each value in the iterator, and should return either true if the value is a match, or false if it's not.

The first matching value will cause iteration to stop.

If no match is found then null is returned.

Example

print! (10..20).find |x| x > 14 and x < 16
check! 15

print! (10..20).find |x| x > 100
check! null

flatten

|Iterable| -> Iterator

Returns the output of the input iterator, with any nested iterable values flattened out.

Note that only one level of flattening is performed, so any double-nested containers will still be present in the output.

Example

print! [(2, 4), [6, 8, (10, 12)]]
  .flatten()
  .to_list()
check! [2, 4, 6, 8, (10, 12)]

See Also

fold

|
  input: Iterable, 
  initial_value: Any, 
  accumulator: |accumulated: Any, next: Any| -> Any
| -> Any

Returns the result of 'folding' the iterator's values into an accumulator function.

The function takes the accumulated value and the next iterator value, and then returns the result of folding the value into the accumulator.

The first argument is an initial accumulated value that gets passed to the function along with the first value from the iterator.

The result is then the final accumulated value.

This operation is also known in other languages as reduce, accumulate, inject, fold left, along with other names.

Example

print! ('a', 'b', 'c')
  .fold [], |result, x| 
    result.push x
    result.push '-'
check! ['a', '-', 'b', '-', 'c', '-']

See Also

generate

|generator: || -> Any| -> Iterator

Creates an iterator that yields the result of repeatedly calling the generator function.

Warning: This version of generate will iterate endlessly, so consider using an adaptor like iterator.take to produce an iterator that has an end.

|n: Number, generator: || -> Any| -> Any

Creates an iterator that yields the result of calling the generator function n times.

Example

from iterator import generate

state = {x: 0}
f = || state.x += 1

print! generate(f)
  .take(5)
  .to_list()
check! [1, 2, 3, 4, 5]

print! generate(3, f).to_tuple()
check! (6, 7, 8)

See Also

intersperse

|Iterable, value: Any| -> Iterator

Returns an iterator that yields a copy of the provided value between each adjacent pair of output values.

|Iterable, generator: || -> Any| -> Iterator

Returns an iterator that yields the result of calling the provided function between each adjacent pair of output values.

Example

print! ('a', 'b', 'c').intersperse('-').to_string()
check! a-b-c

separators = (1, 2, 3).iter()
print! ('a', 'b', 'c')
  .intersperse || separators.next().get()
  .to_tuple(),
check! ('a', 1, 'b', 2, 'c')

iter

|Iterable| -> Iterator

Returns an iterator that yields the provided iterable's values.

Iterable values will be automatically accepted by most iterator operations, so it's usually not necessary to call .iter(), however it can be usefult sometimes to make a standalone iterator for manual iteration.

Note that calling .iter with an Iterator will return the iterator without modification. If a copy of the iterator is needed then see koto.copy and koto.deep_copy.

Example

i = (1..10).iter()
i.skip 5
print! i.next().get()
check! 6

See Also

keep

|Iterable, test: |Any| -> Bool| -> Iterator

Returns an iterator that keeps only the values that pass a test function.

The function is called for each value in the iterator, and should return either true if the value should be kept in the iterator output, or false if it should be discarded.

Example

print! 0..10
  .keep |x| x % 2 == 0
  .to_tuple()
check! (0, 2, 4, 6, 8)

last

|Iterable| -> Any

Consumes the iterator, returning the last yielded value.

Example

print! (1..100).take(5).last()
check! 5

print! (0..0).last()
check! null

max

|Iterable| -> Any

Returns the maximum value found in the iterable.

|Iterable, key: |Any| -> Any| -> Any

Returns the maximum value found in the iterable, based on first calling a 'key' function with the value, and then using the resulting keys for the comparisons.

A < 'less than' comparison is performed between each value and the maximum found so far, until all values in the iterator have been compared.

Example

print! (8, -3, 99, -1).max()
check! 99

See Also

min

|Iterable| -> Any

Returns the minimum value found in the iterable.

|Iterable, key: |Any| -> Any| -> Any

Returns the minimum value found in the iterable, based on first calling a 'key' function with the value, and then using the resulting keys for the comparisons.

A < 'less than' comparison is performed between each value and the minimum found so far, until all values in the iterator have been compared.

Example

print! (8, -3, 99, -1).min()
check! -3

See Also

min_max

|Iterable| -> (Any, Any)

Returns the minimum and maximum values found in the iterable.

|Iterable, key: |Any| -> Any| -> Any

Returns the minimum and maximum values found in the iterable, based on first calling a 'key' function with the value, and then using the resulting keys for the comparisons.

A < 'less than' comparison is performed between each value and both the minimum and maximum found so far, until all values in the iterator have been compared.

Example

print! (8, -3, 99, -1).min_max()
check! (-3, 99)

See Also

next

|Iterable| -> IteratorOutput

Returns the next value from the iterator wrapped in an IteratorOutput, or null if the iterator has been exhausted.

Example

x = (1, null, 'x').iter()
print! x.next()
check! IteratorOutput(1)
print! x.next()
check! IteratorOutput(null)
print! x.next()
check! IteratorOutput(x)
print! x.next()
check! null

# Call .get() to access the value from an IteratorOutput
print! 'abc'.next().get()
check! a

See Also

next_back

|Iterable| -> IteratorOutput

Returns the next value from the end of the iterator wrapped in an IteratorOutput, or null if the iterator has been exhausted.

This only works with iterators that have a defined end, so attempting to call next_back on endless iterators like iterator.generate will result in an error.

Example

x = (1..=5).iter()
print! x.next_back()
check! IteratorOutput(5)
print! x.next_back()
check! IteratorOutput(4)

# calls to next and next_back can be mixed together
print! x.next()
check! IteratorOutput(1)
print! x.next_back()
check! IteratorOutput(3)
print! x.next_back()
check! IteratorOutput(2)

# 1 has already been produced by the iterator, so it's now exhausted
print! x.next_back()
check! null

See Also

once

|Any| -> Iterator

Returns an iterator that yields the given value a single time.

Example

print! iterator.once(99)
  .chain('abc')
  .to_tuple()
check! (99, 'a', 'b', 'c')

See Also

peekable

|Iterable| -> Peekable

Wraps the given iterable value in a peekable iterator.

Peekable.peek

Returns the next value from the iterator without advancing it. The peeked value is cached until the iterator is advanced.

Example

x = 'abc'.peekable()
print! x.peek()
check! IteratorOutput(a)
print! x.peek()
check! IteratorOutput(a)
print! x.next()
check! IteratorOutput(a)
print! x.peek()
check! IteratorOutput(b)
print! x.next(), x.next()
check! (IteratorOutput(b), IteratorOutput(c))
print! x.peek()
check! null

See Also

Peekable.peek_back

Returns the next value from the end of the iterator without advancing it. The peeked value is cached until the iterator is advanced.

Example

x = 'abc'.peekable()
print! x.peek_back()
check! IteratorOutput(c)
print! x.next_back()
check! IteratorOutput(c)
print! x.peek()
check! IteratorOutput(a)
print! x.peek_back()
check! IteratorOutput(b)
print! x.next_back(), x.next_back()
check! (IteratorOutput(b), IteratorOutput(a))
print! x.peek_back()
check! null

See Also

position

|Iterable, test: |Any| -> Bool| -> Any

Returns the position of the first value in the iterable that passes the test function.

The function is called for each value in the iterator, and should return either true if the value is a match, or false if it's not.

The first matching value will cause iteration to stop, and the number of steps taken to reach the matched value is returned as the result.

If no match is found then null is returned.

Example

print! (10..20).position |x| x == 15
check! 5

print! (10..20).position |x| x == 99
check! null

See Also

product

|Iterable| -> Any

Returns the result of multiplying each value in the iterable together, using 1 as the initial value.

Example

# Find the product of a sequence of numbers
print! (2, 3, 4).product()
check! 24

my_type = |n|
  n: n
  @*: |other| my_type self.n * other.n
  @display: || 'my_type({self.n})'

# Find the sum of a sequence of my_type values
print! (my_type(2), my_type(3)).product my_type(10)
check! my_type(60)

See also

repeat

|value: Any| -> Iterator

Creates an iterator that endlessly yields the provided value.

Warning: This version of repeat will iterate endlessly, so consider using an adaptor like iterator.take to produce an iterator with an end.

|value: Any, n: Number| -> Iterator

Creates an iterator that yields n repeats of the provided value.

Example

from iterator import repeat

print! repeat(42).take(5).to_list()
check! [42, 42, 42, 42, 42]

print! repeat('x', 3).to_tuple()
check! ('x', 'x', 'x')

See Also

reversed

|Iterator| -> Iterator

Reverses the order of the iterator's output.

This only works with iterators that have a defined end, so attempting to reverse endless iterators like iterator.generate will result in an error.

Example

print! 'Héllö'.reversed().to_tuple()
check! ('ö', 'l', 'l', 'é', 'H')

print! (1..=10).reversed().skip(5).to_tuple()
check! (5, 4, 3, 2, 1)

skip

|Iterable, steps: Number| -> Iterator

Skips over a number of steps in the iterator.

Example

print! (100..200).skip(50).next().get()
check! 150

See also

step

|Iterable, step_size: Number| -> Iterator

Steps over the iterable's output by the provided step size.

Example

print! (0..10).step(3).to_tuple()
check! (0, 3, 6, 9)

print! 'Héllö'.step(2).to_string()
check! Hlö

See also

sum

|Iterable| -> Any

Returns the result of adding each value in the iterable together, using 0 as the initial value.

|Iterable, initial_value: Any| -> Any

Returns the result of adding each value in the iterable together, using the provided initial value as the start of the operation.

Example

# Find the sum of a sequence of numbers
print! (2, 3, 4).sum()
check! 9

my_type = |n|
  n: n
  @+: |other| my_type self.n + other.n
  @display: || 'my_type({self.n})'

# Find the sum of a sequence of my_type values
print! (my_type(1), my_type(2)).sum my_type(100)
check! my_type(103)

See also

take

|Iterable, count: Number| -> Iterator

Creates an iterator that yields a number of values from the input before finishing.

|Iterable, test: |Any| -> Bool| -> Iterator

Creates an iterator that yields values from the input while they pass a test function.

The test function should return true if the iterator should continue to yield values, and false if the iterator should stop yielding values.

Example

print! (100..200).take(3).to_tuple()
check! (100, 101, 102)

print! 'hey!'.take(|c| c != '!').to_string()
check! hey

See also

to_list

|Iterable| -> List

Consumes all values coming from the iterator and places them in a list.

Example

print! ('a', 42, (-1, -2)).to_list()
check! ['a', 42, (-1, -2)]

See also

to_map

|Iterable| -> Map

Consumes all values coming from the iterator and places them in a map.

If a value is a tuple, then the first element in the tuple will be inserted as the key for the map entry, and the second element will be inserted as the value.

If the value is anything other than a tuple, then it will be inserted as the map key, with null as the entry's value.

Example

print! ('a', 'b', 'c').to_map()
check! {a: null, b: null, c: null}

print! ('a', 'bbb', 'cc')
  .each |x| x, size x
  .to_map()
check! {a: 1, bbb: 3, cc: 2}

See also

to_string

|Iterable| -> String

Consumes all values coming from the iterator and produces a string containing the formatted values.

Example

print! ('x', 'y', 'z').to_string()
check! xyz

print! (1, 2, 3).intersperse('-').to_string()
check! 1-2-3

See also

to_tuple

|Iterable| -> Tuple

Consumes all values coming from the iterator and places them in a tuple.

Example

print! ('a', 42, (-1, -2)).to_tuple()
check! ('a', 42, (-1, -2))

See also

windows

|Iterable, size: Number| -> Iterator

Returns an iterator that splits up the input data into overlapping windows of the specified size, where each window is provided as a Tuple.

If the input has fewer elements than the window size, then no windows will be produced.

Example

print! 1..=5
  .windows 3
  .to_list(),
check! [(1, 2, 3), (2, 3, 4), (3, 4, 5)]

zip

|first: Iterable, second: Iterable| -> Iterator

Combines the values in two iterables into an iterator that yields corresponding pairs of values, one at a time from each input iterable.

Example

print! (1, 2, 3)
  .zip ('a', 'b', 'c')
  .to_list()
check! [(1, 'a'), (2, 'b'), (3, 'c')]

IteratorOutput

A wrapper for a single item of iterator output.

This exists to allow functions like iterator.next to return null to indicate that the iterator has been exhausted, while also allowing null to appear in the iterator's output.

IteratorOutput.get

|IteratorOutput| -> Any

Returns the wrapped iterator output value.

Example

print! x = 'abc'.next()
check! IteratorOutput(a)
print! x.get()
check! a