phoe/cafe-latte

An implementation of Common Lisp dynamic variables, control flow operators, and condition system in plain Java.

Cafe Latte

"We were not out to win over the Lisp programmers; we were after the C++ programmers. We managed to drag a lot of them about halfway to Lisp."

--- Guy Steele, Java spec co-author

"Notice that no one mentions that this way they also managed to drag a lot of Lisp programmers about halfway back to C++."

--- Michał "phoe" Herda, angry Internet rando

About

This is an implementation of Common Lisp dynamic variables, control flow operators, and condition system in plain Java.

If Portable Conditon System is a proof that a Common Lisp condition system can be implemented on a Common Lisp implementation without a condition system of its own, then Cafe Latte is a proof that a Common Lisp-inspired condition system can be implemented even on top of a non-Lisp language that has only automatic memory management and a primitive unwinding operator (in this case, throw), but does not support dynamic variables or non-local returns by default.

It should be possible to use it, or parts of it, in other projects, and its source code should be readable enough to understand the underlying mechanics of each Lisp control flow operator.

Using Cafe Latte

This library is not yet documented, but the respective implementations should behave analogously to their Common Lisp counterparts; see the Common Lisp HyperSpec for their descriptions.

Example uses of the various constructs implemented here are present in the test directory, containing unit tests for all the present mechanisms.

A stable release of this library will be made when the authors are satisfied enough with its functioning.

License

AGPLv3. (Unless you are @easye, at which point it's whatever license suits you the best.)

What's DONE

• Dynamic variables
  • Dynamic variable class
    • Implemented in the DynamicVariable class.
    • Unit tests done.
• Control flow
  • tagbody/go
    • Implemented in the Tagbody class.
    • Unit tests done.
  • block/return-from
    • Implemented in the Block class.
    • Unit tests done.
  • throw/catch
    • Because of Java naming conflicts, catch/throw are renamed to grasp/fling.
    • Implemented in the Grasp class.
    • Unit tests done.
    • throw/catch are not required for implementing a condition system, but their implementations are nonetheless included here for completeness.
• Conditions
  • Condition class
    • Implemented in the Condtion class.
    • Subtype of RuntimeException.
    • Do not fill in the stack trace when instantiated; see the superFillInStackTrace() method.
  • Warning class
    • Implemented in the Warning class.
    • Subtype of Condition.
  • Error class
    • Implemented in the Error class.
    • Subtype of Condition.
• Handlers
  • Handler class
    • Implemented in the Handler class.
    • Tested elsewhere.
  • signal
    • Implemented in the Handler class as a static method.
    • Tested elsewhere.
  • warn
    • Implemented in the Handler class as a static method.
    • Unit tests done.
  • error
    • Implemented in the Handler class as a static method.
    • Unit tests done.
  • *break-on-signals*
    • Implemented in the Handler class as a dynamic variable.
    • Unit tests done.
  • handler-bind
    • Implemented in the HandlerBind class.
    • Unit tests done.
  • handler-case
    • Implemented in the HandlerCase class.
    • Unit tests done.
  • ignore-errors
    • Implemented in the HandlerCase class as a static method.
    • Unit tests done.
• Restarts
  • Restart class
    • Implemented in the Restart class.
    • Unit tests done.
  • restart-bind
    • Implemented in the RestartBind class.
    • Unit tests done.
  • restart-case
    • Implemented in the RestartCase class.
    • Unit tests done.
  • with-simple-restart
    • Implemented in the RestartCase class as a static method.
    • Unit tests done.
• Debugger
  • Debugger interface
    • Defined in the Debugger class.
  • *debugger-hook*
    • Implemented in the Debugger class as a dynamic variable.
    • Unit tests done.
  • break
    • Implemented in the Debugger class as a static method.
    • Unit tests done.
    • Because of Java naming conflicts, break is renamed to breakIntoDebugger.
  • No debugger
    • Implemented in the NoDebugger class.
    • Tested along with the Error class by means of calling the static error method.

What's TODO

• Condition reports
  • Should map nicely to the standard Java exception toString mechanism.
• Restart reports
  • Should map nicely to the standard Java exception toString mechanism.
• Interactive debugger
• JShell as debugger REPL

What's WONTDO

• unwind-protect - Java has try/finally that is fully equivalent.