6.2.17. Local Fixity DeclarationsΒΆ
A careful reading of the Haskell 98 Report reveals that fixity
declarations (infix
, infixl
, and infixr
) are permitted to
appear inside local bindings such those introduced by let
and
where
. However, the Haskell Report does not specify the semantics of
such bindings very precisely.
In GHC, a fixity declaration may accompany a local binding:
let f = ...
infixr 3 `f`
in
...
and the fixity declaration applies wherever the binding is in scope. For
example, in a let
, it applies in the right-hand sides of other
let
-bindings and the body of the let
C. Or, in recursive do
expressions (The recursive do-notation), the local fixity
declarations of a let
statement scope over other statements in the
group, just as the bound name does.
Moreover, a local fixity declaration must accompany a local binding of that name: it is not possible to revise the fixity of name bound elsewhere, as in
let infixr 9 $ in ...
Because local fixity declarations are technically Haskell 98, no extension is necessary to enable them.