August 2014
Intermediate to advanced
120 pages
2h 45m
English
Content preview from Mastering Clojure Macros
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Error Handling in Macros
Most macros, like our pattern matching example in the previous section, have very specific sets of input that they accept, and will throw strange-looking errors when those input expectations aren’t satisfied. For instance, if we didn’t realize that snore.match only handled vectors as input, we might try to match against a keyword, which would give us this error:
| language_features/error_handling_1.clj | |
| | (match :foo |
| | :oh "hi" |
| | :foo "bar" |
| | :else "else") |
| | UnsupportedOperationException count not supported on this type: Keyword |
| | clojure.lang.RT.countFrom (RT.java:556) |
| | java.lang.UnsupportedOperationException: count not supported on this type: Keyword |
| | RT.java:556 clojure.lang.RT.countFrom |
| | RT.java:530 clojure.lang.RT.count ... |
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