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https://github.com/emlyn/clj-macro-test
A demonstration of an issue when trying to test macros
https://github.com/emlyn/clj-macro-test
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A demonstration of an issue when trying to test macros
- Host: GitHub
- URL: https://github.com/emlyn/clj-macro-test
- Owner: emlyn
- License: epl-2.0
- Created: 2019-11-21T19:34:16.000Z (almost 5 years ago)
- Default Branch: master
- Last Pushed: 2019-11-21T22:21:50.000Z (almost 5 years ago)
- Last Synced: 2024-10-10T19:22:28.003Z (27 days ago)
- Language: Clojure
- Size: 6.84 KB
- Stars: 0
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# macro-test
A demonstration of an issue when trying to test macros
## Usage
The core namespace contains a macro.
It is not important what it is for this demonstration, any macro will do.
In this case I copied a simple `infix` macro from [here](https://www.braveclojure.com/writing-macros/#Anatomy_of_a_Macro).
Run the tests with `lein test`. One assertion will fail:
``` shell
> lein test
lein test macro-test.core-test
lein test :only macro-test.core-test/infix-test
FAIL in (infix-test) (core_test.clj:7)
This fails: the macro is not expanded
expected: (= (quote (+ 1 1)) (macroexpand (quote (infix (1 + 1)))))
actual: (not (= (+ 1 1) (infix (1 + 1))))
Ran 1 tests containing 3 assertions.
1 failures, 0 errors.
Tests failed.
```
Notice how `macroexpand` did not expand the macro, but just returned the form unchanged.
Let's try running the test from a repl. First start up a repl with `lein repl`, then:
``` clojure
macro-test.core=> (require 'macro-test.core-test)
nil
macro-test.core=> (in-ns 'macro-test.core-test)
#object[clojure.lang.Namespace 0x4ae0e040 "macro-test.core-test"]
macro-test.core-test=> (infix-test)
nil
```
Nothing is printed, which means the test passed. How come?
It turns out that `clojure.test` calls the test function from a different namespace.
Let's try doing that:
``` clojure
macro-test.core-test=> (in-ns 'user)
#object[clojure.lang.Namespace 0x58d743 "user"]
user=> (macro-test.core-test/infix-test)
FAIL in (infix-test) (core_test.clj:7)
This fails: the macro is not expanded
expected: (= (quote (+ 1 1)) (macroexpand (quote (infix (1 + 1)))))
actual: (not (= (+ 1 1) (infix (1 + 1))))
nil
```
Now we see the same failure!
We can replicate this `macroexpand` behaviour by calling it from the same or different namespaces:
``` clojure
macro-test.user=> (macroexpand '(infix (1 + 1)))
(infix (1 + 1))
macro-test.user=> (in-ns 'macro-test.core-test)
#object[clojure.lang.Namespace 0x4ae0e040 "macro-test.core-test"]
macro-test.core-test=> (macroexpand '(infix (1 + 1)))
(+ 1 1)
```
Now it becomes clearer what's going wrong.
Trying to macroexpand a macro can only work if there is a macro in scope to expand,
but in the `user` namespace, there is no `infix` macro.
We could work around this by fully qualifying the macro name (and any symbols passed in as arguments),
like `(macroexpand '(macro-test.core/infix (1 + 1)))`.
Or we could use a syntax-quote instead: `(macroexpand ``(infix (1 + 1)))`,
which will automatically qualify all symbols.
Although that includes the `+`, so instead of the expected `(+ 1 1)` result,
we get `(clojure.core/+ 1 1)`.
But maybe it would be better if clojure would run the tests in their own namespace
so that we don't have to use any workarounds?
## License
Copyright © 2019 FIXME
This program and the accompanying materials are made available under the
terms of the Eclipse Public License 2.0 which is available at
http://www.eclipse.org/legal/epl-2.0.
This Source Code may also be made available under the following Secondary
Licenses when the conditions for such availability set forth in the Eclipse
Public License, v. 2.0 are satisfied: GNU General Public License as published by
the Free Software Foundation, either version 2 of the License, or (at your
option) any later version, with the GNU Classpath Exception which is available
at https://www.gnu.org/software/classpath/license.html.