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Enhanced try and throw for Clojure leveraging Clojure's capabilities
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README.md

slingshot

Enhanced throw and catch for Clojure

Provides try+ and throw+. Each is 100% compatible with Clojure and Java's native try and throw both in source code and at runtime. Each also provides new capabilities intended to improve ease of use by leveraging Clojure's other capabilities like record types and destructuring.

Clojure's try and throw behave much like those of Java: throw can accept objects derived from java.lang.Throwable and try selects from among catch clauses based on the class of the thrown object.

In addition to fully supporting those uses (whether they originate from Clojure code or from Java code via interop), try+ and throw+ provide these enhanced capabilities:

  • throw+ can throw any java object, not just those whose class is derived from java.lang.Throwable. Clojure records become an easy, natural way to represent custom exceptions without requiring gen-class. Clojure hash-maps with :type metadata also work well.

  • catch clauses within try+ can catch any java object thrown by throw+ Clojure's throw, or Java's throw. The selector can be a class name (e.g., Integer, my.clojure.record, IllegalArgumentException), or a keyword representing a clojure type (as used by isa?, derive, etc.).

  • handle clauses within try+ will match against any arbitrary predicate applied to the thrown object.

  • The binding to the caught exception in a catch clause is no longer required to be a simple symbol. It is now subject to destructuring so the body of the catch clause can use the contents of a thrown collection (record, set, map, vector) easily.

  • In a catch clause, the context at the throw site is accessible via the hidden argument &throw-context. The context includes the stack trace and the environment: bound locals and their values.

Usage

  • See the tests for examples

Credits

  • Based on clojure.contrib.condition, data-conveying-exception, discussions on the clojure mailing list and wiki and discussions and implementations by Steve Gilardi, Phil Hagelberg, and Kevin Downey.

License

Copyright (C) 2011 Stephen Gilardi, Kevin Downey, and Phil Hagelberg

Distributed under the Eclipse Public License, the same as Clojure.

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