diff options
| -rw-r--r-- | doc/guix.texi | 14 | ||||
| -rw-r--r-- | guix/monads.scm | 5 |
2 files changed, 14 insertions, 5 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 diff --git a/guix/monads.scm b/guix/monads.scm index fe3d5d78f1..317f85d079 100644 --- a/guix/monads.scm +++ b/guix/monads.scm @@ -185,8 +185,9 @@ form is (VAR -> VAL), bind VAR to the non-monadic value VAL in the same way as (define-syntax mbegin (syntax-rules (%current-monad) - "Bind the given monadic expressions in sequence, returning the result of -the last one." + "Bind MEXP and the following monadic expressions in sequence, returning +the result of the last expression. Every expression in the sequence must be a +monadic expression." ((_ %current-monad mexp) mexp) ((_ %current-monad mexp rest ...) |