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Diffstat (limited to 'doc/propspecs.rst')
| -rw-r--r-- | doc/propspecs.rst | 34 |
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diff --git a/doc/propspecs.rst b/doc/propspecs.rst index 7143f37..a3f8900 100644 --- a/doc/propspecs.rst +++ b/doc/propspecs.rst @@ -6,3 +6,37 @@ Combinators Currently supported: ``(unapply (foo 1 2 3))``, ``((foo 1 2 3) on-change (bar 4 5 6) on-change (baz 7 8 9))`` and combinations thereof. + +Unevaluated property application specifications +----------------------------------------------- + +In an atomic property application within an unevaluated property application +specification, if the symbol naming the property ends with the character +``.``, then the following special evaluation rules apply: + +1. The property to be applied is the property named by the symbol in the same + package and with the same name as the first element of the atomic property + application, but with the trailing period removed from the name. + +2. The first argument is not evaluated if it is a list whose first element is + a keyword, or a if it is a list of lists where the first element of the + first list is a keyword. + +3. The last argument is treated as an unevaluated property application + specification and is converted into a property application specification + according to the usual evaluation rules. + +This is intended to make applications of properties like DEPLOYS, +DEPLOYS-THESE and CHROOT:DEBOOTSTRAPPED, which take property application +specifications as arguments, easier to read and write in the most common +cases. For example, you can write:: + + (deploys. (:ssh (:sudo :as "spwhitton@athena.example.com")) athena.example.com + ((additional-property val1) + (a-further-property val2))) + +instead of:: + + (deploys '(:ssh (:sudo :as "spwhitton@athena.example.com")) athena.example.com + `((additional-property ,val1) + (a-further-property ,val2))) |