chickadee » lazy-seq

lazy-seq

A lazy sequence implementation inspired by Clojure's. It is an alternative to SRFI 41. See this article for the motivation of creating this egg and a comparison with SRFI 41.

API

make-lazy-seq bodyprocedure

Returns a lazy-seq object. body is a thunk which will be called when the sequence is realized. It is expected to return one of the following things:

  • The empty list to signify the end of the sequence
  • A pair with the sequence's head in the car and a lazy-seq representing the sequence's tail in the cdr
  • Another lazy-seq which will be realized recursively when the sequence is realized
(lazy-seq body ...)syntax

Convenience syntax for make-lazy-seq with body ... being the thunk's body.

lazy-seq? seqprocedure

Predicate for checking whether seq is a lazy-seq.

lazy-seq-realized? seqprocedure

Predicate for checking whether seq has already been realized.

lazy-null? seqprocedure

Predicate for checking whether seq is null. Realizes seq.

lazy-list #!rest elementsprocedure

Returns a realized lazy-seq of elements.

lazy-nullconstant

A null lazy-seq.

lazy-seq->list seqprocedure

Completely realizes seq and returns a list of its elements. Should not be called on infinite sequences.

list->lazy-seq listprocedure

Turns list into a realized lazy-seq.

lazy-head seqprocedure

Realizes seq and returns its head.

lazy-tail seqprocedure

Realizes seq and returns its tail.

lazy-length seqprocedure

Completely realizes seq and returns its length. Should not be called on infinite sequences.

lazy-append seqs ...procedure

Returns a lazy-seq representing the concatenation of seqs.

lazy-concatenate seqprocedure

Returns a lazy-seq representing the concatenation of the lazy-seqs contained in seq.

lazy-append-map proc seqs ...procedure

Returns a lazy-seq which is the concatenation of lazy-seqs resulting from applying proc to each element in seqs.

lazy-reverse seqprocedure

Returns a lazy-seq of the reversed seq. Note that even realizing just the head of the returned lazy-seq will realize seq completely. Infinite sequences can't be reversed.

lazy-take n seqprocedure

Returns a lazy-seq of the first n elements of seq.

lazy-drop n seqprocedure

Returns a lazy-seq of all but the first n elements of seq.

lazy-take-while pred? seqprocedure

Returns a lazy-seq of all leading elements of seq satisfying pred?.

lazy-drop-while pred? seqprocedure

Returns a lazy-seq of seq without all leading elements satisfying pred?.

lazy-ref n seqprocedure

Realizes seq up to the nth element and returns that element.

lazy-map proc seqs ...procedure

Returns a lazy-seq of applying proc to each element in seqs. Terminates with the sortest of seqs.

lazy-filter pred? seqprocedure

Returns a lazy-seq of elements from seq satisfying pred?.

lazy-each proc seqs ...procedure

Completely realizes seqs and applies proc to each item for its side-effect. Terminates with the sortest of seqs.

lazy-fold kons init seqprocedure

Completely realizes seq, iterating over each value and accumulating a result, similar to fold from srfi-1.

lazy-flatten seqprocedure

Returns a lazy-seq of elements from seq, expanding any contained lazy-seq elements. The result is a single flat lazy-seq.

lazy-iterate proc xprocedure

Returns a lazy-seq with a head of x and a tail of applying proc to the preceding element.

lazy-repeat xprocedure

Returns an infinite lazy-seq of x.

lazy-repeatedly thunkprocedure

Returns an infinite lazy-seq of the return value of thunk at the time an element is realized.

lazy-cycle seqprocedure

Returns a lazy-seq which infinitely cycles through seq.

lazy-numbers #!key (step 1) (start 0) countprocedure

Returns a lazy-seq of numbers starting at start and increasing by step. When count is a positive number the sequence terminates after count elements. Otherwise it is infinte.

input-port->lazy-seq port readprocedure

Returns a lazy-seq of the results of applying read to port (which must be an input port). The sequence terminates when read returns #!eof. The port is not closed automatically by this procedure.

lazy-seq->string seqprocedure

Completely realizes a seq of characters and returns a string consisting of those characters. Should not be called on infinite sequences.

string->lazy-seq stringprocedure

Turns string into a realized lazy-seq of characters.

Examples

Defining a custom lazy-seq

(define odd-numbers
  (let next ((n 1))
    (lazy-seq
     (cons n (next (+ n 2))))))

(lazy-ref 5 odd-numbers) ; => 11

Note that odd-numbers can be defined more conveniently like this:

(define odd-numbers
  (lazy-filter odd? (lazy-numbers)))

About this egg

Source

The source code is hosted at Bitbucket. Feel free to fork it and send pull requests there.

Author

Moritz Heidkamp

Version history

2
First version to be compatible with CHICKEN 5. Various code improvements.

For previous versions, see documentation of the CHICKEN 4 version of this egg.

License

 Copyright (c) 2018, Moritz Heidkamp
 All rights reserved.
 
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