monads: Hide 'derivation-expression' and 'lower-inputs'.

* guix/monads.scm: Unexport 'lower-inputs' and 'derivation-expression'.
  (text-file*): Add comment about the switch to 'gexp->derivation'.
  (lower-inputs): Add comment about its doom.
  (derivation-expression): Likewise.
* guix/gexp.scm (lower-inputs*): Rename to...
  (lower-inputs): ... this.  Update callers.
* tests/monads.scm (derivation-expression): New procedure.
* doc/guix.texi (The Store Monad): Use 'gexp->derivation' instead of
  'derivation-expression'.  Remove documentation of
  'derivation-expression'.
* guix/ui.scm (read/eval): Use THE-ROOT-MODULE so that macros are
  properly expanded.
* tests/guix-build.sh: Use 'gexp->derivation' instead of
  'derivation-expression'.monads: Hide 'derivation-expression' and 'lower-inputs'.

doc/guix.texi

@@ -1868,11 +1868,12 @@ Consider this ``normal'' procedure:
 
 Using @code{(guix monads)}, it may be rewritten as a monadic function:
 
+@c FIXME: Find a better example, one that uses 'mlet'.
 @example
 (define (sh-symlink)
   ;; Same, but return a monadic value.
-  (mlet %store-monad ((sh (package-file bash "bin")))
-    (derivation-expression "sh" `(symlink ,sh %output))))
+  (gexp->derivation "sh"
+                    #~(symlink (string-append #$bash "/bin/bash") #$output)))
 @end example
 
 There are two things to note in the second version: the @code{store}
@@ -1973,15 +1974,6 @@ directory of @var{package}.  When @var{file} is omitted, return the name
 of the @var{output} directory of @var{package}.
 @end deffn
 
-@deffn {Monadic Procedure} derivation-expression @var{name} @var{exp} @
-       [#:system (%current-system)] [#:inputs '()] @
-       [#:outputs '("out")] [#:hash #f] @
-       [#:hash-algo #f] [#:env-vars '()] [#:modules '()] @
-       [#:references-graphs #f] [#:guile-for-build #f]
-Monadic version of @code{build-expression->derivation}
-(@pxref{Derivations}).
-@end deffn
-
 @deffn {Monadic Procedure} package->derivation @var{package} [@var{system}]
 Monadic version of @code{package-derivation} (@pxref{Defining
 Packages}).

guix/gexp.scm

@@ -66,10 +66,9 @@ (define-record-type <output-ref>
 (define raw-derivation
   (store-lift derivation))
 
-(define (lower-inputs* inputs)
+(define (lower-inputs inputs)
   "Turn any package from INPUTS into a derivation; return the corresponding
 input list as a monadic value."
-  ;; XXX: This is like 'lower-inputs' but without the "name" part in tuples.
   (with-monad %store-monad
     (sequence %store-monad
               (map (match-lambda
@@ -101,7 +100,7 @@ (define* (gexp->derivation name exp
   (define %modules modules)
   (define outputs (gexp-outputs exp))
 
-  (mlet* %store-monad ((inputs   (lower-inputs* (gexp-inputs exp)))
+  (mlet* %store-monad ((inputs   (lower-inputs (gexp-inputs exp)))
                        (sexp     (gexp->sexp exp #:outputs outputs))
                        (builder  (text-file (string-append name "-builder")
                                             (object->string sexp)))

guix/monads.scm

@@ -57,9 +57,7 @@ (define-module (guix monads)
             text-file*
             package-file
             package->derivation
-            built-derivations
-            derivation-expression
-            lower-inputs)
+            built-derivations)
   #:replace (imported-modules
              compiled-modules))
 
@@ -356,6 +354,7 @@ (define (builder inputs)
        (lambda (port)
          (display ,(computed-text text inputs) port))))
 
+  ;; TODO: Rewrite using 'gexp->derivation'.
   (mlet %store-monad ((inputs (lower-inputs inputs)))
     (derivation-expression name (builder inputs)
                            #:inputs inputs)))
@@ -376,7 +375,7 @@ (define* (package-file package
 (define (lower-inputs inputs)
   "Turn any package from INPUTS into a derivation; return the corresponding
 input list as a monadic value."
-  ;; XXX: Should probably be in (guix packages).
+  ;; XXX: This procedure is bound to disappear with 'derivation-expression'.
   (with-monad %store-monad
     (sequence %store-monad
               (map (match-lambda
@@ -390,6 +389,7 @@ (define (lower-inputs inputs)
                    inputs))))
 
 (define derivation-expression
+  ;; XXX: This procedure is superseded by 'gexp->derivation'.
   (store-lift build-expression->derivation))
 
 (define package->derivation

guix/ui.scm

@@ -241,7 +241,7 @@ (define (read/eval str)
                         str args)))))
     (catch #t
       (lambda ()
-        (eval exp the-scm-module))
+        (eval exp the-root-module))
       (lambda args
         (leave (_ "failed to evaluate expression `~a': ~s~%")
                exp args)))))

tests/guix-build.sh

@@ -1,5 +1,5 @@
 # GNU Guix --- Functional package management for GNU
-# Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
+# Copyright © 2012, 2013, 2014 Ludovic Courtès <ludo@gnu.org>
 #
 # This file is part of GNU Guix.
 #
@@ -75,7 +75,8 @@ then false; else true; fi
 
 # Invoking a monadic procedure.
 guix build -e "(begin
-                 (use-modules (guix monads) (guix utils))
+                 (use-modules (guix gexp))
                  (lambda ()
-                   (derivation-expression \"test\" '(mkdir %output))))" \
+                   (gexp->derivation \"test\"
+                                     (gexp (mkdir (ungexp output))))))" \
    --dry-run

tests/monads.scm

@@ -108,6 +108,9 @@ (define (g x)
                       guile)))
     #:guile-for-build (package-derivation %store %bootstrap-guile)))
 
+(define derivation-expression
+  (@@ (guix monads) derivation-expression))
+
 (test-assert "mlet* + derivation-expression"
   (run-with-store %store
     (mlet* %store-monad ((guile  (package-file %bootstrap-guile "bin/guile"))