7.9 Unit Contracts
| (unit/c | | (import sig-block ...) | | (export sig-block ...) | | init-depends-decl | | optional-body-ctc) |
|
| |
| sig-block | | = | | (tagged-sig-id [id contract] ...) | | | | | | | tagged-sig-id | | | | | | | | init-depends-decl | | = | | | | | | | | | (init-depend tagged-sig-id ...) | | | | | | | | optional-body-ctc | | = | | | | | | | | | contract | | | | | | | (values contract ...) |
|
A
unit contract wraps a unit and checks both its imported and
exported identifiers to ensure that they match the appropriate contracts.
This allows the programmer to add contract checks to a single unit value
without adding contracts to the imported and exported signatures.
The unit value must import a subset of the import signatures and export a
superset of the export signatures listed in the unit contract. Additionally,
the unit value must declare initialization dependencies that are a subset of
those specified in the unit contract. Any identifier which is not listed
for a given signature is left alone. Variables used in a given
contract expression first refer to other variables in the same
signature, and then to the context of the unit/c expression.
If a body contract is specified then the result of invoking the unit value
is wrapped with the given contract, if no body contract is supplied then
no wrapping occurs when the unit value is invoked.
|
| |
| sig-spec-block | | = | | (tagged-sig-spec [id contract] ...) | | | | | | | tagged-sig-spec | | | | | | | | optional-body-ctc | | = | | | | | | | | | #:invoke/contract contract | | | | | | | #:invoke/contract (values contract ...) |
|
The
define-unit/contract form defines a unit compatible with
link inference whose imports and exports are contracted with a unit
contract. The unit name is used for the positive blame of the contract.