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ADR-017: clarify IsShelleyBasedEra vs type families distinction #88

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ADR-017: clarify IsShelleyBasedEra vs type families distinction #88

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Clarify IsShelleyBasedEra vs type families in ADR-017
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10 changes: 8 additions & 2 deletions docs/ADR-017-Cardano-Api-Compatible.md
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Expand Up @@ -106,8 +106,14 @@ type family StakeRegistrationRequirements era where

This design means callers provide the correct data for each era
without needing to pattern-match on era witnesses themselves.
The `IsShelleyBasedEra` constraint on the certificate functions
dispatches to the correct ledger operations internally.
Note that `IsShelleyBasedEra` and the type families are distinct concerns:
the type families determine the *types* of arguments at the call site (compile time),
while the certificate functions also carry an `IsShelleyBasedEra era` constraint
that provides the era singleton (`ShelleyBasedEra era`) used at runtime
to dispatch to the correct ledger operations for each era.
Callers in a polymorphic-era context must therefore include
`IsShelleyBasedEra era` (or a stronger constraint that implies it,
such as `IsBabbageBasedEra era`) in their own type signatures.

### Handling Governance Differences with GADTs

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