Taps

A library of conveniences for working with SERIES

Introduction

Richard Waters' SERIES package for Common Lisp provides a powerful and interesting solution to working with sequences, collections, and streams. The Taps library adds a small number of functions that make SERIES more convenient to work with in many common situations.

A tap in the real world is a device that opens and closes a valve, enabling a fluid to flow or preventing it from doing so. In the Taps library, a tap is a function that turns some data structure into a series of values. Taps provides functions that create series from streams, strings, and iterative computations, and provides convenient functions for mapping over, filtering, and collecting results.

The workflow for which Taps is designed is this:

1. Call a function to tap a data structure, creating a flow of values
2. Select or filter the values of interest using another function
3. Map another function over the selected values to produce a series of outputs
4. Collect the results using a collector function

Used judiciously, Taps can make many looping or iterative processes easier to write and easier to read.

Taps Reference

This section describes the functions that make up the Taps library. The generic function tap is the heart of the library, but several utility functions are also provided for mapping over series, collecting values from them, and so on.

In most cases a function that operates on series also works if its arguments are Common Lisp sequences. For example, you can use take to collect values from a series, but it works just as well to collect values from lists, strings, or vectors.

Variables

+line-break-characters+ Special variable
The default set of characters used to break lines of text.

+whitespace-characters+ Special variable
The default set of characters treated as whitespace.

Functions

any Generic function

any (series) => value

Returns an arbitrary element of series.

Warning: any works only on sequences and finite series. If applied to an infinite series it will never return.

contains? Generic function

contains? (series value &key (test 'eql))=> Boolean

Returns true if value is a member of the series. test is used to compare value to elements of the series.

Warning: contains? works only on sequences and finite series. If applied to an infinite series it will never return.

drop Generic function

drop (n series) => series*

Returns a new series containing all the elements of series except for the first n elements.

filter Function

filter (fn series) => series*

Returns a new series, series* created by mapping fn over the elements of series and collecting those for which fn returns a true value.

leave Generic function

leave (n series) => series*

Returns a new series containing the last n elements of series.

Warning: leave works only on sequences and finite series. If applied to an infinite series it will never return.

tails Generic function

tails (series) => series*

Returns a new series of series. Each member series is constructed by dropping the first element of the previous series. If series is finite, then each tail will be finite. If it's inifnite, then the tails will be, too. Be careful how you use it; for example, (tails (tap-integers)) returns an infinite series of infinite series.

tails-by Generic function

tails-by (n series) => series*

Returns a new series of series. Each member series is constructed by dropping the first n elements of the previous series. If series is finite, then each tail will be finite. If it's inifnite, then the tails will be, too. Be careful how you use it; for example, (tails-by n (tap-integers)) returns an infinite series of infinite series.

take Generic function

take (n series) => series*

Returns a new series that contains the first n elements of series.

take-by Generic function

take-by (n series) => series*

Returns a new series created by splitting series into shorter series, each one containing n elements of series.

take-m-by-n Generic function

take-m-by-n (m n series) => series*

Returns a new series created by repeatedly collecting m elements of series, starting with the first element of series and moving the starting point forward each time by n.

take-until Function

take-until (predicate series) => series*

Returns a new series created by collecting elements from the start of series until applying predicate to an element returns a true value.

tap Generic function

tap (element-type source &key &allow-other-keys) => series

Returns a new series created by computing a (possibly infinite) series of values from source. The type of values and the method used to compute them depends on both element-type and source.

element-type	source	Description
:bytes	stream	Returns a series of bytes read from the stream.
:bytes	pathname	Returns a series of bytes read from the file.
:characters	stream	Returns a series of characters read from the stream.
:characters	pathname	Returns a series of character read from the file.
:characters	string	Returns a series of characters read from the string.
:words	stream	Returns a series of 'words' read from the stream. Pass the keyword argument :word-break-characters with a list of characters to control text is broken into words.
:words	pathname	Returns a series of 'words' read from the file. Pass the keyword argument :word-break-characters with a list of characters to control text is broken into words.
:words	string	Returns a series of 'words' read from the string. Pass the keyword argument :word-break-characters with a list of characters to control text is broken into words.
:lines	stream	Returns a series of lines of text read from the stream. Pass the keyword argument :line-break-characters with a list of characters to control how text is broken into lines.
:lines	pathname	Returns a series of lines of text read from the file. Pass the keyword argument :line-break-characters with a list of characters to control how text is broken into lines.
:lines	string	Returns a series of lines of text read from the string. Pass the keyword argument :line-break-characters with a list of characters to control how text is broken into lines.
:objects	stream	Returns a series of Lisp objects read from the stream.
:objects	pathname	Returns a series of Lisp objects read from the file.
:objects	string	Returns a series of Lisp objects read from the string.
:hash-entries	hash-table	Returns two series as multiple values: a series of the keys in the hash-table, and a series of its corresponding values.
:keys	hash-table	Returns a series containing the keys from the hash-table.
:values	hash-table	Returns a series containing the values from the hash-table.

tap-fn Function

tap-fn (fn series) => series

Returns a new series of values computed by mapping the function fn over the elements of series.

tap-integers Function

tap-integers (&key from by upto below downto above) => series

Returns a new series of integers. The first element of the series is from, whose default value is zero. Each successive element is obtained by adding the value of by to the previous one. THe default value of by is one. If upto is supplied then the series continues until the next element is greater than upto. If below is supplied, it continues until the next element is greater than or equal to below. If downto is supplied, it continues until the next element is less than downto. If above is supplied then it continues until the next element is less than or equal to above.

The series returned by tap-integers may be of infinite length. For example, the expression

(tap-integers)

returns an infinite series that starts with

#Z(0 1 2 3 ...

tap-random-integers Function

tap-random-integers (below &optional (random-state *random-state*)) => series

Returns an infinite series of random integers, each less than below.