deep-nth ( index-seq nested-seq -- elt )

Vocabulary

sequences.extras

Inputs

index-seq	a sequence
nested-seq	a sequence

Outputs

elt

an object

Word description

A version of nth that drills into a nested seq. Gets element n1 from nested-seq, then element n2 from that result, and so on, where n1, n2, etc come from index-seq. When index-seq is exhausted, the result is put on the stack. Note that this usage of "deep" is different from those in sequences.deep.

Examples

An empty index-seq leaves nested-seq on the stack:

USING: sequences.extras prettyprint ; { } { 1 2 3 } deep-nth .
{ 1 2 3 }

An index-seq with one element is the same as calling nth with that element:

USING: kernel sequences sequences.extras prettyprint ; { 1 } "abc" deep-nth 1 "abc" nth = .
t

Multiple elements in index-seq act like repeated calls to nth:

USING: sequences.extras prettyprint ; { 1 1 } { "zero" { "one-zero" "one-one" } } deep-nth .
"one-one"

Errors

Throws a bounds-error if any of the indices are negative, or greater than or equal to the length of nested-seq (at the corresponding nesting level).

Definition

USING: sequences ;

IN: sequences.extras

: deep-nth ( index-seq nested-seq -- elt ) [ nth-of ] reduce ;