diff options
| -rw-r--r-- | nix/yants/default.nix | 23 | ||||
| -rw-r--r-- | nix/yants/tests/default.nix | 7 |
2 files changed, 30 insertions, 0 deletions
diff --git a/nix/yants/default.nix b/nix/yants/default.nix index 6da99fa3c8c4..3e9a4c00a29a 100644 --- a/nix/yants/default.nix +++ b/nix/yants/default.nix @@ -296,4 +296,27 @@ in lib.fix (self: { in sig: func: if length sig < 2 then (throw "Signature must at least have two types (a -> b)") else defun' sig func; + + # Restricting types + # + # `restrict` wraps a type `t`, and uses a predicate `pred` to further + # restrict the values, giving the restriction a descriptive `name`. + # + # First, the wrapped type definition is checked (e.g. int) and then the + # value is checked with the predicate, so the predicate can already + # depend on the value being of the wrapped type. + restrict = name: pred: t: + let restriction = "${t.name}[${name}]"; in typedef' { + name = restriction; + checkType = v: + let res = t.checkType v; + in + if !(t.checkToBool res) + then res + else { + ok = pred v; + err = "${prettyPrint v} does not conform to restriction '${restriction}'"; + }; + }; + }) diff --git a/nix/yants/tests/default.nix b/nix/yants/tests/default.nix index da539ca3562b..8ad306df932b 100644 --- a/nix/yants/tests/default.nix +++ b/nix/yants/tests/default.nix @@ -92,4 +92,11 @@ deepSeq rec { (struct { a = int; b = option string; }) (sum { a = int; b = option string; }) ]; + + testRestrict = [ + ((restrict "< 42" (i: i < 42) int) 25) + ((restrict "not too long" (l: builtins.length l < 3) (list int)) [ 1 2 ]) + (list (restrict "eq 5" (v: v == 5) any) [ 5 5 5 ]) + ]; + } (pkgs.writeText "yants-tests" "All tests passed!") |