monads: Add 'mbegin'.

* guix/monads.scm (mbegin): New macro.
* tests/monads.scm ("mbegin"): New test.
* doc/guix.texi (The Store Monad): Document it.

1 files changed, 9 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index ed2b81ba33..c9760f5f60 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -2061,6 +2061,15 @@ Bind the variables @var{var} to the monadic values @var{mval} in
 (@pxref{Local Bindings,,, guile, GNU Guile Reference Manual}).
 @end deffn
 
+@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.
+
+This is akin to @code{mlet}, except that the return values of the
+monadic expressions are ignored.  In that sense, it is analogous to
+@code{begin}, but applied to monadic expressions.
+@end deffn
+
 The interface to the store monad provided by @code{(guix monads)} is as
 follows.