| Safe Haskell | None |
|---|---|
| Language | GHC2024 |
Settei.Config
Description
A Config describes configuration effects without reading a source. Independent
settings compose with Applicative; runtime-dependent effects compose with
Control.Selective. The latter preserves a static over-approximation while allowing
an interpreter to skip an unused branch.
For example, a caller can declare a production-only password (assuming
environmentSetting :: Setting Text and passwordSetting :: Setting Text):
productionPassword :: Config (Maybe Text) productionPassword = whenEq (required environmentSetting) "production" (required passwordSetting)
Inspection needs no environment variables or files:
fmap (renderKey . schemaSettingKey) (schemaNecessary (describe productionPassword)) -- ["runtime.environment"]
For arbitrary selective branch shapes, use select directly; the
production-only declaration above desugars to:
select
((environment -> if environment == "production" then Left () else Right Nothing)
<$> required environmentSetting)
((password _ -> Just password) <$> required passwordSetting)
Config intentionally has no Monad instance. Monadic binding could construct new
keys from resolved values and would make complete static inspection impossible.
Synopsis
- data Config a
- describe :: Config a -> Schema
- fallbackTo :: Config (Maybe a) -> Config a -> Config a
- optional :: Setting a -> Config (Maybe a)
- required :: Setting a -> Config a
- whenConfig :: Config Bool -> Config a -> Config (Maybe a)
- whenEq :: Eq d => Config d -> d -> Config a -> Config (Maybe a)
- withDefault :: Setting a -> Default a -> Config a
Documentation
The private, typed syntax tree behind the public declaration language.
describe :: Config a -> Schema Source #
Inspect every possible request without reading configuration sources.
fallbackTo :: Config (Maybe a) -> Config a -> Config a Source #
Use the first declaration's value when present; otherwise evaluate the fallback.
This is the key-migration idiom:
optional newSetting reads a renamed key and
consults the old key only when no source supplies the new one.fallbackTo required oldSetting
Desugars to select. Schema footprint: the primary declaration's
settings keep their presence; the fallback's settings become conditional; one
Condition row records the primary's possible keys as dependencies and
the fallback's possible keys as activated settings. The alias is declaration-level,
not per-source: a value for the primary key in any source, however low its precedence,
suppresses the fallback entirely.
optional :: Setting a -> Config (Maybe a) Source #
Request a setting without failing when no source supplies it.
required :: Setting a -> Config a Source #
Require one setting when this declaration path is evaluated.
whenConfig :: Config Bool -> Config a -> Config (Maybe a) Source #
Evaluate a declaration only when a condition is True.
Desugars to select; no new syntax is introduced. Schema
footprint: every setting inside the condition keeps its presence (a required
condition setting stays necessary); every setting inside the branch becomes
conditional; one Condition row is recorded whose dependencies are the
condition's possible keys and whose activated settings are the branch's possible keys.
At resolution time a False condition reports the branch's settings as not selected
rather than missing.
whenEq :: Eq d => Config d -> d -> Config a -> Config (Maybe a) Source #
Evaluate a declaration only when a scrutinee equals an expected value.
whenEq (required environmentSetting) Production (required passwordSetting)Production. Schema
footprint is identical to whenConfig: scrutinee settings keep their presence,
branch settings become conditional, and one Condition row links them.