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iterator -- get an iterator



An iterator is an object that is used to traverse through x. Usually, but not necessarily, this will be an instance of the Iterator class.

i1 : iter = iterator {1, 2, 3}

o1 = iterator {1, 2, 3}

o1 : Iterator

The class of an iterator should have a next method installed that gets the next element of x.

i2 : next iter

o2 = 1
i3 : next iter

o3 = 2
i4 : next iter

o4 = 3

If x contains only a finite number of elements, then next should return the symbol StopIteration after exhausting them all.

i5 : next iter

o5 = StopIteration

o5 : Symbol

Instances of classes with this method installed can be used like lists in for loops and scan.

i6 : lookup(iterator, String)

o6 = -*Function[../../../../../Macaulay2/m2/iterators.m2:16:26-23:12]*-

o6 : FunctionClosure
i7 : for i in "foo" list i

o7 = {f, o, o}

o7 : List
i8 : scan("foo", print)

They can also be passed to apply and select. In each case, an Iterator object will be returned that is an iterator for itself.

i9 : apply("foo", toUpper)

o9 = (F, O, O)

o9 : Sequence
i10 : for i in oo list i

o10 = {F, O, O}

o10 : List
i11 : select("foo", i -> i == "o")

o11 = iterator "foo"

o11 : Iterator
i12 : for i in oo list i

o12 = {o, o}

o12 : List

See also

Ways to use iterator :

For the programmer

The object iterator is a method function with a single argument.