SRFI 140: Immutable Strings

by Per Bothner

status: final (2017-05-24)

keywords: Data Structure

See also SRFI 118: Simple adjustable-size strings and SRFI 135: Immutable Texts.


This attempts to solve the same issues with R7RS strings raised by SRFI-135, but with better integration with the Scheme language.

We propose to retain the name string as the type of sequences of Unicode characters (scalar values). There are two standard subtypes of string:

An implementation may support other kinds of strings. For example on the Java platform it may be reasonable to consider any instance of java.lang.CharSequence to be a string.

The main part of the proposal specifies the default bindings of various procedure names, as might be pre-defined in a REPL. Specifically, some procedures that traditionally return mutable strings are changed to return istrings. We later discuss compatibility and other library issues.

This combines SRFI-13, SRFI-135, and SRFI-118.