6.0
- Support for `define-type', `struct:', `make-predicate', etc. at the REPL
- Performance work: optimized subtyping
- Make `struct:' have the correct bindings in struct info
- Use pairs for objects on arrow types
- Split off `recover-source-syntax' into a separate package and generalized it
- Lots of doc improvements
- Lots of error message improvements
- Split into multiple packages
5.3.4
- Moved Optimization Coach to the package system
- Multiple fixes to polydots
5.3.3
  No changes
5.3.2
- Added types for control operators
- Added `typed/untyped-utils`
5.3.1
- Revised handling of `Any` exported to untyped code
- Added `cast`
- Correctly compute variance of polymorphic type application
5.3
- Keyword and optional arguments
- Faster startup
- Random testing of the numeric tower
5.2.1
- Inference of functions with keyword arguments
- `typecheck-fail' for explicit creation of type errors
- Extensive documentation of typed numeric tower
5.2
- Performance work: delayed environment evaluation
- Support `racket'-style optional arguments
- Changes to support new-style keyword argument expansion
