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authorLudovic Courtès <ludo@gnu.org>2015-06-08 22:49:50 +0200
committerLudovic Courtès <ludo@gnu.org>2015-06-08 23:00:49 +0200
commit751630c9c3f7f3e87dfccc5f5ba8cf61cdd6f8fd (patch)
tree2da2fcf7e6e300c98f2777e0bcb5670252ff4803 /doc
parentae9b96c7846cc7d4528da5c6d861d6440cf46e33 (diff)
downloadpatches-751630c9c3f7f3e87dfccc5f5ba8cf61cdd6f8fd.tar
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monads: Allow n-ary '>>=' expressions.
Suggested by Federico Beffa <beffa@fbengineering.ch>. * guix/monads.scm (bind-syntax): New macro. (with-monad): Use it instead of 'identifier-syntax'. * tests/monads.scm (">>= with more than two arguments"): New test. * doc/guix.texi (The Store Monad): Explain that there can be several MPROC. Add an example.
Diffstat (limited to 'doc')
-rw-r--r--doc/guix.texi23
1 files changed, 18 insertions, 5 deletions
diff --git a/doc/guix.texi b/doc/guix.texi
index bcfa52d5b1..85ccd4057e 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -2773,12 +2773,25 @@ in @var{monad}.
Return a monadic value that encapsulates @var{val}.
@end deffn
-@deffn {Scheme Syntax} >>= @var{mval} @var{mproc}
+@deffn {Scheme Syntax} >>= @var{mval} @var{mproc} ...
@dfn{Bind} monadic value @var{mval}, passing its ``contents'' to monadic
-procedure @var{mproc}@footnote{This operation is commonly referred to as
-``bind'', but that name denotes an unrelated procedure in Guile. Thus
-we use this somewhat cryptic symbol inherited from the Haskell
-language.}.
+procedures @var{mproc}@dots{}@footnote{This operation is commonly
+referred to as ``bind'', but that name denotes an unrelated procedure in
+Guile. Thus we use this somewhat cryptic symbol inherited from the
+Haskell language.}. There can be one @var{mproc} or several of them, as
+in this example:
+
+@example
+(run-with-state
+ (with-monad %state-monad
+ (>>= (return 1)
+ (lambda (x) (return (+ 1 x)))
+ (lambda (x) (return (* 2 x)))))
+ 'some-state)
+
+@result{} 4
+@result{} some-state
+@end example
@end deffn
@deffn {Scheme Syntax} mlet @var{monad} ((@var{var} @var{mval}) ...) @