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Diffstat (limited to 'docs/users_guide/exts/applicative_do.rst')
| -rw-r--r-- | docs/users_guide/exts/applicative_do.rst | 9 |
1 files changed, 4 insertions, 5 deletions
diff --git a/docs/users_guide/exts/applicative_do.rst b/docs/users_guide/exts/applicative_do.rst index 460ae3d162..a46d74d957 100644 --- a/docs/users_guide/exts/applicative_do.rst +++ b/docs/users_guide/exts/applicative_do.rst @@ -71,9 +71,11 @@ is as follows. If the do-expression has the following form: :: where none of the variables defined by ``p1...pn`` are mentioned in ``E1...En``, and ``p1...pn`` are all variables or lazy patterns, -then the expression will only require ``Applicative``. Otherwise, the expression +then the expression will only require ``Applicative``. The do expression may also +contain ``let`` statements anywhere, provided that the right-hand-sides of the ``let`` +bindings do not mention any of ``p1...pn``. Otherwise, the expression will require ``Monad``. The block may return a pure expression ``E`` depending -upon the results ``p1...pn`` with either ``return`` or ``pure``. +upon the results ``p1...pn`` and the ``let`` bindings, with either ``return`` or ``pure``. Note: the final statement must match one of these patterns exactly: @@ -187,6 +189,3 @@ terms of ``Monad`` is to use the ``Monad`` operations directly, e.g. :: instance Applicative MyType where pure = return (<*>) = ap - - - |