wren

a classy little scripting language

Sequence Class

An abstract base class for any iterable object. Any class that implements the core iterator protocol can extend this to get a number of helpful methods.

Methods #

all(predicate) #

Tests whether all the elements in the sequence pass the predicate.

Iterates over the sequence, passing each element to the function predicate. If it returns something false, stops iterating and returns the value. Otherwise, returns true.

System.print([1, 2, 3].all {|n| n > 2}) false
System.print([1, 2, 3].all {|n| n < 4}) true

any(predicate) #

Tests whether any element in the sequence passes the predicate.

Iterates over the sequence, passing each element to the function predicate. If it returns something true, stops iterating and returns that value. Otherwise, returns false.

System.print([1, 2, 3].any {|n| n < 1}) false
System.print([1, 2, 3].any {|n| n > 2}) true

contains(element) #

Returns whether the sequence contains any element equal to the given element.

count #

The number of elements in the sequence.

Unless a more efficient override is available, this will iterate over the sequence in order to determine how many elements it contains.

count(predicate) #

Returns the number of elements in the sequence that pass the predicate.

Iterates over the sequence, passing each element to the function predicate and counting the number of times the returned value evaluates to true.

System.print([1, 2, 3].count {|n| n > 2}) 1
System.print([1, 2, 3].count {|n| n < 4}) 3

each(function) #

Iterates over the sequence, passing each element to the given function.

["one", "two", "three"].each {|word| System.print(word) }

isEmpty #

Returns whether the sequence contains any elements.

This can be more efficient that count == 0 because this does not iterate over the entire sequence.

join(separator) #

Converts every element in the sequence to a string and then joins the results together into a single string, each separated by separator.

It is a runtime error if separator is not a string.

join() #

Converts every element in the sequence to a string and then joins the results together into a single string.

map(transformation) #

Creates a new sequence that applies the transformation to each element in the original sequence while it is iterated.

var doubles = [1, 2, 3].map {|n| n * 2 } 
for (n in doubles) { 
  System.print(n) 2
                  4
                  6
}

The returned sequence is lazy. It only applies the mapping when you iterate over the sequence, and it does so by holding a reference to the original sequence.

This means you can use map(_) for things like infinite sequences or sequences that have side effects when you iterate over them. But it also means that changes to the original sequence will be reflected in the mapped sequence.

To force eager evaluation, just call .toList on the result.

var numbers = [1, 2, 3] 
var doubles = numbers.map {|n| n * 2 }.toList 
numbers.add(4) 
System.print(doubles) [2, 4, 6]

reduce(function) #

Reduces the sequence down to a single value. function is a function that takes two arguments, the accumulator and sequence item and returns the new accumulator value. The accumulator is initialized from the first item in the sequence. Then, the function is invoked on each remaining item in the sequence, iteratively updating the accumulator.

It is a runtime error to call this on an empty sequence.

reduce(seed, function) #

Similar to above, but uses seed for the initial value of the accumulator. If the sequence is empty, returns seed.

toList #

Creates a list containing all the elements in the sequence.

System.print((1..3).toList)  [1, 2, 3]

If the sequence is already a list, this creates a copy of it.

where(predicate) #

Creates a new sequence containing only the elements from the original sequence that pass the predicate.

During iteration, each element in the original sequence is passed to the function predicate. If it returns false, the element is skipped.

var odds = (1..6).where {|n| n % 2 == 1 } 
for (n in odds) { 
    System.print(n) 1
                    3
                    5
}

The returned sequence is lazy. It only applies the filtering when you iterate over the sequence, and it does so by holding a reference to the original sequence.

This means you can use where(_) for things like infinite sequences or sequences that have side effects when you iterate over them. But it also means that changes to the original sequence will be reflected in the filtered sequence.

To force eager evaluation, just call .toList on the result.

var numbers = [1, 2, 3, 4, 5, 6] 
var odds = numbers.where {|n| n % 2 == 1 }.toList 
numbers.add(7) 
System.print(odds) [1, 3, 5]