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authorChris Marusich <cmmarusich@gmail.com>2017-04-06 02:28:36 -0700
committerLudovic Courtès <ludo@gnu.org>2017-04-08 14:40:51 +0200
commit8bc2183fe54487793e9eb6b39ba01329671840b9 (patch)
treefeb0db0228724d2631871c4baf3bf621af764eb4 /doc/guix.texi
parent60a9fcb1377e4acc78a930904ef80b69a1c63f25 (diff)
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monads: Improve mlet, mlet*, and mbegin documentation.
* doc/guix.texi (The Store Monad) <mlet, mlet*, mbegin>: Clarify their intended usage. * guix/monads.scm (mbegin): Update docstring accordingly. Signed-off-by: Ludovic Courtès <ludo@gnu.org>
Diffstat (limited to 'doc/guix.texi')
-rw-r--r--doc/guix.texi14
1 files changed, 11 insertions, 3 deletions
diff --git a/doc/guix.texi b/doc/guix.texi
index 62f4483b85..974d9b3a4f 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -4038,8 +4038,15 @@ in this example:
@deffnx {Scheme Syntax} mlet* @var{monad} ((@var{var} @var{mval}) ...) @
@var{body} ...
Bind the variables @var{var} to the monadic values @var{mval} in
-@var{body}. The form (@var{var} -> @var{val}) binds @var{var} to the
-``normal'' value @var{val}, as per @code{let}.
+@var{body}, which is a sequence of expressions. As with the bind
+operator, this can be thought of as ``unpacking'' the raw, non-monadic
+value ``contained'' in @var{mval} and making @var{var} refer to that
+raw, non-monadic value within the scope of the @var{body}. The form
+(@var{var} -> @var{val}) binds @var{var} to the ``normal'' value
+@var{val}, as per @code{let}. The binding operations occur in sequence
+from left to right. The last expression of @var{body} must be a monadic
+expression, and its result will become the result of the @code{mlet} or
+@code{mlet*} when run in the @var{monad}.
@code{mlet*} is to @code{mlet} what @code{let*} is to @code{let}
(@pxref{Local Bindings,,, guile, GNU Guile Reference Manual}).
@@ -4047,7 +4054,8 @@ Bind the variables @var{var} to the monadic values @var{mval} in
@deffn {Scheme System} mbegin @var{monad} @var{mexp} ...
Bind @var{mexp} and the following monadic expressions in sequence,
-returning the result of the last expression.
+returning the result of the last expression. Every expression in the
+sequence must be a monadic expression.
This is akin to @code{mlet}, except that the return values of the
monadic expressions are ignored. In that sense, it is analogous to