### 6.2 Regular Expressions ¶

MIT/GNU Scheme provides support for matching and searching strings against regular expressions. This is considerably more flexible than ordinary string matching and searching, but potentially much slower. On the other hand it is less powerful than the mechanism described in Parser Language.

Traditional regular expressions are defined with string patterns in which characters like ‘`[`’ and ‘`*`’ have special meanings. Unfortunately, the syntax of these patterns is not only baroque but also comes in many different and mutually-incompatible varieties. As a consequence we have chosen to specify regular expressions using an s-expression syntax, which we call a regular s-expression, abbreviated as regsexp.

Previous releases of MIT/GNU Scheme provided a regular-expression implementation nearly identical to that of GNU Emacs version 18. This implementation supported only 8-bit strings, which made it unsuitable for use with Unicode strings. This implementation still exists but is deprecated and will be removed in a future release.