packages: Add 'lookup-package-input' & co.

* guix/packages.scm (lookup-input, lookup-package-input)
(lookup-package-native-input, lookup-package-propagated-input)
(lookup-package-direct-input): New procedures.
* doc/guix.texi (package Reference): Document them.

1 files changed, 34 insertions, 0 deletions

diff --git a/guix/packages.scm b/guix/packages.scm
index 37814c2f63..ac5ff5a51b 100644
--- a/guix/packages.scm
+++ b/guix/packages.scm
@@ -108,6 +108,11 @@
             deprecated-package
             package-field-location
 
+            lookup-package-input
+            lookup-package-native-input
+            lookup-package-propagated-input
+            lookup-package-direct-input
+
             package-direct-sources
             package-transitive-sources
             package-direct-inputs
@@ -889,6 +894,35 @@ preserved, and only duplicate propagated inputs are removed."
       ((input rest ...)
        (loop rest (cons input result) propagated first? seen)))))
 
+(define (lookup-input inputs name)
+  "Lookup NAME among INPUTS, an input list."
+  ;; Note: Currently INPUTS is assumed to be an input list that contains input
+  ;; labels.  In the future, input labels will be gone and this procedure will
+  ;; check package names.
+  (match (assoc-ref inputs name)
+    ((obj) obj)
+    ((obj _) obj)
+    (#f #f)))
+
+(define (lookup-package-input package name)
+  "Look up NAME among PACKAGE's inputs.  Return it if found, #f otherwise."
+  (lookup-input (package-inputs package) name))
+
+(define (lookup-package-native-input package name)
+  "Look up NAME among PACKAGE's native inputs.  Return it if found, #f
+otherwise."
+  (lookup-input (package-native-inputs package) name))
+
+(define (lookup-package-propagated-input package name)
+  "Look up NAME among PACKAGE's propagated inputs.  Return it if found, #f
+otherwise."
+  (lookup-input (package-propagated-inputs package) name))
+
+(define (lookup-package-direct-input package name)
+  "Look up NAME among PACKAGE's direct inputs.  Return it if found, #f
+otherwise."
+  (lookup-input (package-direct-inputs package) name))
+
 (define (package-direct-sources package)
   "Return all source origins associated with PACKAGE; including origins in
 PACKAGE's inputs."