monotonic? ( seq quot: ( elt1 elt2 -- ? ) -- ? )
Factor handbook » The language » Collections » Sequence operations » Groups and clumps

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Vocabulary
grouping

Inputs

seq	a sequence
quot	a quotation with stack effect ( elt1 elt2 -- ? )

Outputs

?

a boolean

Word description
Applies the relation to successive pairs of elements in the sequence, testing for a truth value. The relation should be a transitive relation, such as a total order or an equality relation.

Examples
Testing if a sequence is non-decreasing:

USING: grouping math prettyprint ; { 1 1 2 } [ <= ] monotonic? .
t

Testing if a sequence is decreasing:

USING: grouping math prettyprint ; { 9 8 6 7 } [ > ] monotonic? .
f

See also
all-eq?, all-equal?

Definition

USING: kernel math sequences sequences.private ;

IN: grouping

: monotonic? ( seq quot: ( elt1 elt2 -- ? ) -- ? )
    over length dup 2 <
    [ 3drop t ] [
        2 =
        [ [ first2-unsafe ] dip call ] [
            [
                [ first-unsafe ] [
                    >underlying< [ nth-unsafe ] curry
                    [ 1 + ] 2dip
                ] bi
            ] dip [ keep swap ] curry compose all-integers-from?
            nip
        ] if
    ] if ; inline