This page is part of the web mail archives of SRFI 118 from before July 7th, 2015. The new archives for SRFI 118 contain all messages, not just those from before July 7th, 2015.
I think we're ready to finalize: http://srfi.schemers.org/srfi-118/srfi-118.html I fixed some typos, and added some notes on execution speed. I've attached a diff relative to the previous version. -- --Per Bothner per@xxxxxxxxxxx http://per.bothner.com/
--- srfi-118-2015-02-15.html 2015-02-15 07:56:46.131606612 -0800
+++ srfi-118.html 2015-04-19 21:42:31.457553138 -0700
@@ -20,7 +20,7 @@
<body>
<div class="title">
-<H1>Title</H1>
+<h1>Title</h1>
Simple adjustable-size strings
</div>
@@ -52,8 +52,8 @@
Scheme specifies mutable fixed-length strings.
We add two procedures <code>string-append!</code> and
<code>string-replace!</code> which allow the size of the string to change.
-We also require that standard Scheme procedures that return mutable strings
-(such as <code>make-string</code>) return variable-size strings.
+We also require that the standard Scheme procedures <code>make-string</code>
+and <code>string-copy</code> return variable-size strings.
</p><h1>Rationale</h1>
<p>
@@ -131,7 +131,7 @@
appending each <var>value</var> (in order) to the end of <var>string</var>.
A <var>value</var> can be a character or a string.
</p><p>
-The following example show to to process a string using
+The following example shows how to process a string using
<code>string-for-each</code> and incrementally <q>building</q> a result string
using <code>string-append!</code>:</p>
<pre>(define (translate-space-to-newline str)
@@ -146,6 +146,8 @@
str)
result))
</pre>
+<p>There is no requirement that this procedure execute in constant time,
+even amortised (i.e. average) constant time.
<p><em>Usage note:</em> Compare with using string ports:</p>
<pre>(define (translate-space-to-newline str)
(let ((out (open-output-string)))
@@ -166,7 +168,7 @@
but that depends on the strategy used by <code>string-append!</code>
when the allocated buffer is too small.
The <code>string-append!</code> function is most useful when
-using (reading) a string a interleaved with growing it,
+using (reading) a string is interleaved with growing it,
or when also using <code>string-replace!</code>.
</blockquote>
@@ -196,6 +198,11 @@
<p>
The implementation is trivial, assuming there is some indirection
between the string object header and the actual stored characters.
+Whenever the character buffer is full, it needs to be replaced with
+a bigger buffer. If the size of the new buffer is a
+fixed multiple of the size of the old buffer then
+ <code>string-append!</code> has amortized constant execution time.
+(The multiple 1.5 <a href="http://stackoverflow.com/questions/1100311/what-is-the-ideal-growth-rate-for-a-dynamically-allocated-array";>seems a good choice</a>.)
</p><p>
If you have cheap Smalltalk-style <code>becomes:</code> (which is admittedly
unlikely these days) then you can use that when you need to grow a string