Control.Ether.Abbr

Abbreviations for constraints.

Documentation

data tag --> r

Denotes MonadReader. The mnemonic is that you read values of type r from the reader environment tagged by tag, thus the arrows points from tag to r.

Instances

type ReifyAbbr ((-->) tag r) m = MonadReader tag r m

data tag <-- w

Denotes MonadWriter. The mnemonic is that you write values of w to the writer accumulator tagged by tag, thus the arrows points from w to tag.

Instances

type ReifyAbbr ((<--) tag w) m = MonadWriter tag w m

data tag <-> s

Denotes MonadState. The mnemonic is that you can both read from and write into the state, thus the arrow points in both directions.

Instances

type ReifyAbbr ((<->) tag s) m = MonadState tag s m

data tag -!- e

Denotes MonadExcept.

Instances

type ReifyAbbr ((-!-) tag e) m = MonadExcept tag e m

type family Ether abbrs m :: Constraint

Reify a list of constraint abbreviations.

f :: Ether '[Foo --> r, Bar <-- w, Baz <-> s, Quux -!- e] m => m a

expands into

f :: ( MonadReader Foo  r m
     , MonadWriter Bar  w m
     , MonadState  Baz  s m
     , MonadExcept Quux e m
     ) => m a

Equations

Ether [] m = ()

Ether (abbr : abbrs) m = (ReifyAbbr abbr m, Ether abbrs m)

type family ReifyAbbr abbr m :: Constraint

Turns an abbreviation into an actual constraint.

Instances

type ReifyAbbr (E e) m = MonadExcept e m

type ReifyAbbr (S s) m = MonadState s m

type ReifyAbbr (W w) m = MonadWriter w m

type ReifyAbbr (R r) m = MonadReader r m

type ReifyAbbr ((-!-) tag e) m = MonadExcept tag e m

type ReifyAbbr ((<->) tag s) m = MonadState tag s m

type ReifyAbbr ((<--) tag w) m = MonadWriter tag w m

type ReifyAbbr ((-->) tag r) m = MonadReader tag r m