7.9 Unit Contracts
| (unit/c | | (import sig-spec-block ...) | | (export sig-spec-block ...) | | init-depends-decl | | optional-body-ctc) |
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| sig-spec-block | | = | | (tagged-sig-spec [id contract] ...) | | | | | | | tagged-sig-spec | | | | | | | | init-depends-decl | | = | | | | | | | | | (init-depend tagged-sig-id ...) | | | | | | | | optional-body-ctc | | = | | | | | | | | | contract | | | | | | | (values contract ...) |
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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 any of the
listed signatures, 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, otherwise the values are returned as-is.
Changed in version 8.8.0.7 of package base: Changed sig-spec-block to allow arbitrary
tagged-sig-specs instead of only allowing tagged-sig-ids.
Made bindings from all signatures visible in the scope of each
contract expression instead of only the bindings from the same
signature. Additionally, contracts on signature bindings are enforced
within contract expressions.
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| sig-spec-block | | = | | (tagged-sig-spec [id contract] ...) | | | | | | | tagged-sig-spec | | | | | | | | optional-body-ctc | | = | | | | | | | | | #:invoke/contract contract | | | | | | | #:invoke/contract (values contract ...) |
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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.
Changed in version 8.8.0.7 of package base: Made bindings from all signatures visible in
the scope of each contract expression instead of only the bindings
from the same signature. Additionally, contracts on signature bindings are
enforced within contract expressions.