* gnu/system/vm.scm (lower-inputs): Move to monads.scm.
(qemu-image): Don't add GRUB-CONFIGURATION to the INPUTS-TO-COPY.
(union, file-union, etc-directory): Move to gnu/system.scm.
(%demo-operating-system): New variable.
(system-qemu-image): Add 'os' parameter. Rewrite in terms of
'operating-system-derivation'.
* guix/monads.scm (lower-inputs): New procedure.
* gnu/system/grub.scm (grub-configuration-file): Change 'entries' to be
a plain list instead of a list of monadic values.
* gnu/system.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.
* guix/monads.scm (<monad>): Turn in a raw SRFI-9 record type.
(define-monad): New macro.
(with-monad): Add a case for when MONAD is a macro.
(identity-return, identity-bind, store-return, store-bind): Inline.
(%identity-monad, %store-monad): Use 'define-monad'.
* tests/monads.scm ("monad?"): New test.
* guix/monads.scm: New file.
* tests/monads.scm: New file.
* Makefile.am (MODULES): Add guix/monads.scm.
(SCM_TESTS): Add tests/monads.scm.
* doc/guix.texi (The Store Monad): New node.
(The Store): Reference it.
Ludovic Courtès