[mpd] Lispify the MPD query

Write a small DSL for converting a simple lisp expression to an MPD query
format. This turns, for example:

    (and (= artist "Katatonia") (= album "Last Fair Deal Gone Down"))

Into:

    ((artist == "Katatonia") AND (album == "Last Fair Deal Gone Down"))

The expressions inside ‘query’ are quasi-quoted, so that variable substitution
is possible.

1 files changed, 22 insertions, 0 deletions

diff --git a/mpd/usr/share/scsh/mpd.scm b/mpd/usr/share/scsh/mpd.scm
new file mode 100644
index 0000000..74d297b
--- /dev/null
+++ b/mpd/usr/share/scsh/mpd.scm
@@ -0,0 +1,22 @@
+(define-structure mpd (export query)
+  (open scheme-with-scsh)
+  (begin
+    (define-syntax query
+      (syntax-rules ()
+        ((_ a)
+         (mpd-query-1 `a))))
+
+    (define (mpd-query-equals params)
+      (apply format #f "~s == ~s" params))
+
+    (define (mpd-query-and params)
+      (format #f "~a AND ~a"
+              (mpd-query-1 (car params))
+              (mpd-query-1 (cadr params))))
+
+    (define (mpd-query-1 query)
+      (format #f "(~a)"
+              (let ((op (car query)))
+                (case op
+                  ('= (mpd-query-equals (cdr query)))
+                  ('and (mpd-query-and (cdr query)))))))))