diff mbox series

[bug#75010,1/7] monads: Add 'mmatch'.

Message ID 4bfa279cae2316d7a7a4e0640d13a0763ad86f92.1734798943.git.herman@rimm.ee
State New
Headers
Series Roll back when deployment fails. |

Commit Message

Herman Rimm Dec. 21, 2024, 5:04 p.m. UTC 
  * doc/guix.texi (The Store Monad): Document mmatch.
* guix/monads.scm (mmatch): Add macro.

Change-Id: I558f8e025f6cf788c9fc475e99d49690d7a98f41
---
 doc/guix.texi   |  6 ++++++
 guix/monads.scm | 11 +++++++++++
 2 files changed, 17 insertions(+)

Comments

Ludovic Courtès Dec. 30, 2024, 12:34 p.m. UTC | #1 
Herman Rimm <herman@rimm.ee> skribis:

> * doc/guix.texi (The Store Monad): Document mmatch.
> * guix/monads.scm (mmatch): Add macro.
>
> Change-Id: I558f8e025f6cf788c9fc475e99d49690d7a98f41

[...]

> +@defmac mmatch monad mexp (pattern body) @dots{}
> +Match monadic object @var{mexp} against clause @var{pattern}s, in the

I’m not convinced by this one: usually, monadic procedures take a
“normal” value and return a monadic value.  So the style of this macro
is quite unusual.  Also it doesn’t save much typing compared to an
‘mlet’ followed by ‘match’.

WDYT?

Ludo’.
diff mbox series

Patch

diff --git a/doc/guix.texi b/doc/guix.texi
index f7b7569887..c86f644360 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -11814,6 +11814,12 @@  The Store Monad
 (@pxref{Local Bindings,,, guile, GNU Guile Reference Manual}).
 @end defmac
 
+@defmac mmatch monad mexp (pattern body) @dots{}
+Match monadic object @var{mexp} against clause @var{pattern}s, in the
+order in which they appear.  The last expression of each clause
+@var{body} must be a monadic expression.
+@end defmac
+
 @defmac mbegin monad mexp @dots{}
 Bind @var{mexp} and the following monadic expressions in sequence,
 returning the result of the last expression.  Every expression in the
diff --git a/guix/monads.scm b/guix/monads.scm
index 0bd8ac9315..0e8ca868ce 100644
--- a/guix/monads.scm
+++ b/guix/monads.scm
@@ -1,5 +1,6 @@ 
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2013, 2014, 2015, 2017, 2022 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2024 Herman Rimm <herman@rimm.ee>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -37,6 +38,7 @@  (define-module (guix monads)
             with-monad
             mlet
             mlet*
+            mmatch
             mbegin
             mwhen
             munless
@@ -355,6 +357,15 @@  (define-syntax mlet
              (let ((var temp) ...)
                body ...)))))))
 
+(define-syntax mmatch
+  (syntax-rules ()
+    "Match the monadic object MEXP against the patterns of CLAUSES ...
+in the order in which they appear.  The last expression of each clause
+body must be a monadic expression."
+    ((_ monad mexp clauses ...)
+     (with-monad monad
+       (>>= mexp (match-lambda clauses ...))))))
+
 (define-syntax mbegin
   (syntax-rules (%current-monad)
     "Bind MEXP and the following monadic expressions in sequence, returning