diff options
Diffstat (limited to 'guix/monads.scm')
| -rw-r--r-- | guix/monads.scm | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/guix/monads.scm b/guix/monads.scm index 6ae616aca9..0bd8ac9315 100644 --- a/guix/monads.scm +++ b/guix/monads.scm @@ -1,5 +1,5 @@ ;;; GNU Guix --- Functional package management for GNU -;;; Copyright © 2013, 2014, 2015, 2017 Ludovic Courtès <ludo@gnu.org> +;;; Copyright © 2013, 2014, 2015, 2017, 2022 Ludovic Courtès <ludo@gnu.org> ;;; ;;; This file is part of GNU Guix. ;;; @@ -40,6 +40,7 @@ mbegin mwhen munless + mparameterize lift0 lift1 lift2 lift3 lift4 lift5 lift6 lift7 lift listm foldm @@ -398,6 +399,21 @@ expression." (mbegin %current-monad mexp0 mexp* ...))))) +(define-syntax mparameterize + (syntax-rules () + "This form implements dynamic scoping, similar to 'parameterize', but in a +monadic context." + ((_ monad ((parameter value) rest ...) body ...) + (let ((old-value (parameter))) + (mbegin monad + ;; XXX: Non-local exits are not correctly handled. + (return (parameter value)) + (mlet monad ((result (mparameterize monad (rest ...) body ...))) + (parameter old-value) + (return result))))) + ((_ monad () body ...) + (mbegin monad body ...)))) + (define-syntax define-lift (syntax-rules () ((_ liftn (args ...)) |