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Incompatibilities with R⁵RS

This section enumerates the incompatibilities between this report and the “Revised⁵ report” [R5RS].

This list is not authoritative, but is believed to be correct and complete.

• Case sensitivity is now the default in symbols and character names. This means that code written under the assumption that symbols could be written FOO or Foo in some contexts and foo in other contexts can either be changed, be marked with the new #!fold-case directive, or be included in a library using the include-ci library declaration. All standard identifiers are entirely in lower case.
• The syntax-rules construct now recognizes _ (underscore) as a wildcard, which means it cannot be used as a syntax variable. It can still be used as a literal.
• The R⁵RS procedures exact->inexact and inexact->exact have been renamed to their R⁶RS names, inexact and exact, respectively, as these names are shorter and more correct. The former names are still available in the R⁵RS library.
• The guarantee that string comparison (with string<? and the related predicates) is a lexicographical extension of character comparison (with char<? and the related predicates) has been removed.
• Support for the # character in numeric literals is no longer required.
• Support for the letters s, f, d, and l as exponent markers is no longer required.
• Implementations of string->number are no longer permitted to return #f when the argument contains an explicit radix prefix, and must be compatible with read and the syntax of numbers in programs.
• The procedures transcript-on and transcript-off have been removed.