rope

  1. rope
    1. Description
    2. API
    3. History
    4. Author
    5. License

Description

Ropes, as described in "Ropes, An Alternative to Strings" (1995 - H. Boehm, R. Atkinson, M. Plass).

The source for this egg is available at Bitbucket.

API

[record] rope
[procedure] (rope? object) => boolean
[procedure] (rope-length rope) => integer
[procedure] (rope-depth rope) => integer

A rope is either a leaf containing a string or a binary tree consisting of such leaves.

Length and depth are stored on each node, so rope-length and rope-depth are constant time queries.

rope? simply tests if its argument is a rope.

[procedure] (rope=? rope1 rope2 [ropeN ...]) => boolean

rope=? tests whether two ropes represent the same string. Fast paths are provided on eq?ity and rope-length; otherwise, this comparison is O(n).

[parameter] (current-maximum-leaf-length [n])

current-maximum-leaf-length specifies the maximum string length for rope leaf nodes.

The default value is 512, which should be suitable for most purposes. Setting this value too low will result in frequent rebalancing, adversely affecting performance.

[procedure] (rope-null? rope) => boolean

Tests whether the given rope is empty. Equivalent to (= 0 (rope-length rope)).

[procedure] (rope [string ...]) => rope

Constructs a rope from the given strings. The resulting rope, while not guaranteed to be balanced, should be fairly so.

[procedure] (string->rope string) => rope

Constructs a rope from the given string. The resulting rope is guaranteed to be balanced.

[procedure] (rope->string rope) => string

Returns the full contents of the given rope as a string.

[procedure] (rope-ref rope i) => character

Returns the ith character of the rope, zero-indexed.

[procedure] (subrope rope start [end]) => rope

Returns a subrope consisting of the range of characters starting at the zero-indexed character start and ending at character end, or the end of the rope if no end is given.

[procedure] (rope-append [rope ...]) => rope

Appends the given ropes, trying to keep the resulting rope fairly well-balanced.

[procedure] (rope-concatenate list) => rope

Constructs a new rope from the the given list of ropes, trying to keep the resulting rope fairly well-balanced.

[procedure] (rope-reverse rope)

Constructs a new rope consisting of the characters in the given rope, reversed. This operation is expensive for large ropes (O(n) in the length of the rope, best-case).

[procedure] (rope-balanced? rope) => boolean

Tests whether the given rope is balanced. A rope is balanced if its length is at least F(n+2), where F(n) is the nth fibonacci number and n is the depth of the given rope.

[procedure] (rope-balance rope) => rope

Explicitly rebalances a rope.

The rebalancing strategy used is that described in Boehm, Atkinson & Plass' 1995 paper "Ropes, An Alternative to Strings".

[procedure] (rope-fold f a rope1 [ropeN ...]) => object
[procedure] (rope-for-each f rope1 [ropeN ...]) => void

These procedures implement characterwise fold and for-each over the given ropes.

[procedure] (read-rope [port [length]]) => rope

Reads a rope from the given port, or current-input-port if no port is specified.

If a numerical length argument is given, at most that many characters are read.

The resulting rope is guaranteed to be balanced.

[procedure] (make-rope-iterator rope) => procedure

Returns a cursor procedure over the given rope's characters.

The resulting procedure, when invoked, will return the current character in the rope and advance to the next character. When the characters of the rope are exhausted, the procedure will yield #!eof.

[procedure] (open-input-rope rope) => port

Returns a port from which the contents of the rope can be read. When the end of the rope is reached, subsequent reads will return #!eof.

[procedure] (open-output-rope) => port
[procedure] (get-output-rope [port]) => rope

open-output-rope returns a port to which output can be written and accumulated, until returned as a rope with get-output-rope.

In reality, open-output-rope and open-output-string are the same. Construction of the rope returned by get-output-rope is delayed until that procedure is called, so get-output-rope may be used to return a rope from the accumulated output of ports created by either open-output-rope or open-output-string.

History

Author

Evan Hanson

License

Copyright (c) 2012-2013, 3-Clause BSD.