diff options
| -rw-r--r-- | doc/guix.texi | 14 | ||||
| -rw-r--r-- | guix/monads.scm | 12 |
2 files changed, 22 insertions, 4 deletions
diff --git a/doc/guix.texi b/doc/guix.texi index d0f21edeec..62f4483b85 100644 --- a/doc/guix.texi +++ b/doc/guix.texi @@ -4054,6 +4054,20 @@ monadic expressions are ignored. In that sense, it is analogous to @code{begin}, but applied to monadic expressions. @end deffn +@deffn {Scheme System} mwhen @var{condition} @var{mexp0} @var{mexp*} ... +When @var{condition} is true, evaluate the sequence of monadic +expressions @var{mexp0}..@var{mexp*} as in an @code{mbegin}. When +@var{condition} is false, return @code{*unspecified*} in the current +monad. Every expression in the sequence must be a monadic expression. +@end deffn + +@deffn {Scheme System} munless @var{condition} @var{mexp0} @var{mexp*} ... +When @var{condition} is false, evaluate the sequence of monadic +expressions @var{mexp0}..@var{mexp*} as in an @code{mbegin}. When +@var{condition} is true, return @code{*unspecified*} in the current +monad. Every expression in the sequence must be a monadic expression. +@end deffn + @cindex state monad The @code{(guix monads)} module provides the @dfn{state monad}, which allows an additional value---the state---to be @emph{threaded} through diff --git a/guix/monads.scm b/guix/monads.scm index 6933f7f151..fe3d5d78f1 100644 --- a/guix/monads.scm +++ b/guix/monads.scm @@ -204,8 +204,10 @@ the last one." (define-syntax mwhen (syntax-rules () - "When CONDITION is true, evaluate MEXP0..MEXP* as in an 'mbegin'. When -CONDITION is false, return *unspecified* in the current monad." + "When CONDITION is true, evaluate the sequence of monadic expressions +MEXP0..MEXP* as in an 'mbegin'. When CONDITION is false, return *unspecified* +in the current monad. Every expression in the sequence must be a monadic +expression." ((_ condition mexp0 mexp* ...) (if condition (mbegin %current-monad @@ -214,8 +216,10 @@ CONDITION is false, return *unspecified* in the current monad." (define-syntax munless (syntax-rules () - "When CONDITION is false, evaluate MEXP0..MEXP* as in an 'mbegin'. When -CONDITION is true, return *unspecified* in the current monad." + "When CONDITION is false, evaluate the sequence of monadic expressions +MEXP0..MEXP* as in an 'mbegin'. When CONDITION is true, return *unspecified* +in the current monad. Every expression in the sequence must be a monadic +expression." ((_ condition mexp0 mexp* ...) (if condition (return *unspecified*) |