PLT Scheme v4.0 has been released. PLT Scheme is a family of Scheme implementations, including DrScheme and MzScheme.
This release includes: improved syntax for modules, improved support for optional and keyword function arguments, a new syntax for list comprehensions and iterations, a more complete set of string operations, rewritten and reorganized documentation, improved R5RS and R6RS support, support for mutable pairs, the inclusion of Typed Scheme, and other changes.
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