gnu: a2ps: Improve package style.

* gnu/packages/pretty-print.scm (a2ps)[origin]<snippet>: Use G-expressions.
[arguments]<#:phases>: Use G-expression and SEARCH-INPUT-FILE.

gnu/packages/pretty-print.scm

@@ -27,6 +27,7 @@
 ;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
 
 (define-module (gnu packages pretty-print)
+  #:use-module (guix gexp)
   #:use-module (guix packages)
   #:use-module (guix licenses)
   #:use-module (guix git-download)
@@ -65,14 +66,15 @@
               (modules '((guix build utils)))
               (snippet
                ;; Remove timestamp from the installed 'README' file.
-               '(begin
+               #~(begin
                    (substitute* "etc/README.in"
                      (("@date@")
                       "1st of some month, sometime after 1970"))))))
     (build-system gnu-build-system)
     (arguments
-     '(#:phases
-       (modify-phases %standard-phases
+     (list
+      #:phases
+      #~(modify-phases %standard-phases
           (add-after 'unpack 'skip-failing-tests
             (lambda _
               (substitute* (list "tests/Makefile.am" "tests/Makefile.in")
@@ -86,13 +88,12 @@
                     "tests/styles.tst")
                 (("/bin/rm") (which "rm")))))
           (add-before 'check 'patch-test-files
-           ;; Alternatively, we could unpatch the shebangs in tstfiles
+            ;; Alternatively, we could unpatch the shebangs in tst files.
             (lambda* (#:key inputs #:allow-other-keys)
-             (let ((perl (assoc-ref inputs "perl")))
               (substitute* '("tests/ps-ref/includeres.ps"
                              "tests/gps-ref/includeres.ps")
                 (("/usr/local/bin/perl")
-                  (string-append perl "/bin/perl"))))
+                 (search-input-file inputs "/bin/perl")))
               ;; Some of the reference postscript contain a 'version 3'
               ;; string that in inconsistent with the source text in the
               ;; tstfiles directory.  Erroneous search-and-replace?
@@ -103,8 +104,8 @@
                 (("version 3") "version 2"))
               (substitute* '("tests/ps-ref/psmandup.ps"
                              "tests/gps-ref/psmandup.ps")
-               (("#! */bin/sh") (string-append
-                                 "#!" (which "sh")))))))))
+                (("#! */bin/sh")
+                 (string-append "#!" (which "sh")))))))))
     (native-inputs
      (list gperf groff perl pkg-config))
     (inputs
@@ -116,7 +117,7 @@
 printing.  It accomplishes this by being able to delegate files to external
 handlers, such as Groff and Gzip.  It handles as many steps as is necessary to
 produce a pretty-printed file.  It also includes some extra abilities for
-special cases, such as pretty-printing \"--help\" output.")
+special cases, such as pretty-printing @samp{-help} output.")
     (license gpl3+)))
 
 (define-public trueprint