A PPX rewriter to allow simpler testing of pattern matches rather than full equality. Roughly modelled on EUnit's ?assertMatch macro.
Warning: this is still very early and incomplete.
Please note that this project is released with a Contributor Code of Conduct, version 1.4. By participating in this project you agree to abide by its terms. Please see code_of_conduct.md in this repository for details.
Add this preprocessing step to your dune file's library, executable, or test:
(preprocess (pps ppx_test_match?))
See dune/test for a more complete example or the Dune documentation.
This is still too early to be fully usable but the following are already possible:
let some_ounit_test _ =
let example_tuple = (2, 3) in
(* This will pass: *)
[%test_match? (x, y) when y > x] example_tuple;
(* This will fail: *)
[%test_match? (x, y) when x > y] example_tuple;
(* This will pass: *)
[%test_match? (2, _)] example_tuple
type some_rec = { x : string; y : float }
let some_other_test_with_records =
let example_rec = { x = "hello"; y = 3.14159 } in
(* This will pass: *)
[%test_match? { x = "hello"; _ }] example_rec
type a_variant = A of int
let test_with_variant _ =
(* Will pass: *)
[%test_match? (A a) when a > 4] (A 5)The PPX rewriter will also rewrite duplicated variables as an equality check, for example:
let some_other_ounit_test _ =
let t1 = (1.3, 1.3) in
let t2 = (1.0, 1.01) in
(* This will pass: *)
[%test_match? (x, x)] t1;
(* This will fail: *)
[%test_match? (x, x)] t2
type some_other_rec = { a : int; b : string; c : int }
let another_test _ =
(* This will pass: *)
[%test_match? { a; c = a; _ }] { a = 1; b = "abc"; c = 1 }
type a_variant = A of int
let test_eq_with_variant _ =
(* Will pass: *)
[%test_match? (a, A a)] (2, A 2)
(* Will fail: *)
[%test_match? (a, A a) when a < 5] (6, A 6)Only tuples, records, and variants support this rewriting at the moment.
You can optionally supply a printer argument to test_match that will be used to format a non-matching expression on failure. An example using ppx_deriving to generate the printer:
let test_with_printer _ =
(* This will fail with the following message in a `Failure` exception:
Failed to match (x, x) with value (1, 2)
*)
[%test_match? (x, x)] (1, 2) ~printer:[derive.show: (int * int)]When test_match? sees something like (x, x), it will synthesize the following replacement:
(x, _syn_0x) when x = _syn_0xA more complex example, e.g. ((x, y), x) when y > x) will be rewritten as follows:
((x, y), _syn_0x) when y > x && x = _syn_0xMore occurrences of the same variable are sequentially named, e.g. (a, a, a, b) will be rewritten to:
(a, _syn_0a, _syn_1a, b)ppx_test_match is released under the terms of the MIT license. Please see LICENSE.md for more details.
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