Issue 4421/4: Make music functions callable from Scheme

The functions get their signature checked and optional argument handling
is exactly like in LilyPond, with *unspecified* taking the role of
"\default".

diff --git a/lily/include/music-function.hh b/lily/include/music-function.hh
index aacb646e0de5a7d858eb0a88e392d2e3e3a59606..b0ed99732a6a06abf0f6b03ab44a8c6b09628526 100644 (file)
--- a/lily/include/music-function.hh
+++ b/lily/include/music-function.hh
@@ -31,6 +31,8 @@ public:
   int print_smob (SCM, scm_print_state *);
   SCM get_signature () { return scm1 (); }
   SCM get_function () { return scm2 (); }
+  SCM call (SCM args);
+  LY_DECLARE_SMOB_PROC (&Music_function::call, 0, 0, 1);
 };
 
 #endif /* MUSIC_FUNCTION_HH */

diff --git a/lily/music-function.cc b/lily/music-function.cc
index 35341e3c6d6fae828265b3d11f10f3e7c277daf7..f89b719f60bdcd38e58b2c1927ccfb427f9fe6c5 100644 (file)
--- a/lily/music-function.cc
+++ b/lily/music-function.cc
@@ -18,6 +18,10 @@
 */
 
 #include "music-function.hh"
+#include "lily-parser.hh"
+#include "input.hh"
+#include "music.hh"
+#include "fluid.hh"
 
 const char Music_function::type_p_name_[] = "ly:music-function?";
 
@@ -32,3 +36,140 @@ Music_function::print_smob (SCM port, scm_print_state *)
   /* Non-zero means success.  */
   return 1;
 }
+
+// Used for attaching location information to music expressions in
+// default arguments and return values.  Music expressions taken from
+// the call signature need to be cloned since they are not suitable
+// for multiple use.
+
+static SCM
+with_loc (SCM arg, Fluid &loc, bool clone = true)
+{
+  if (Music *m = unsmob<Music> (arg))
+    {
+      if (clone)
+        {
+          m = m->clone ();
+          arg = m->unprotect ();
+        }
+      if (Input *in = unsmob<Input> (loc))
+        m->set_spot (*in);
+    }
+  return arg;
+}
+
+// A music function call implies walking through the call signature
+// and matching the actual argument list to the signature.  This
+// process is not 1:1 due to the possible presence of optional
+// arguments which are handled quite differently from how GUILE/Scheme
+// usually deal with optional arguments.
+//
+// The argument matching here intentionally closely tracks the
+// semantics of calls via the LilyPond parser as described in
+// <URL:lilypond.org/doc/Documentation/extending/scheme-function-usage>:
+// if an optional argument predicate does not match the next argument
+// from the actual argument list, the default given in the call
+// signature is used instead and all following optional arguments are
+// unconditionally substituted in a similar manner.
+//
+// This skipping of optional arguments can be explicitly initiated by
+// using \default in LilyPond.  The respective value to use for a call
+// via Scheme is *unspecified*.
+
+SCM
+Music_function::call (SCM rest)
+{
+  Fluid parser (ly_lily_module_constant ("%parser"));
+  Fluid location (ly_lily_module_constant ("%location"));
+
+  // (car (ly:music-signature self_scm())) is the return type, skip it
+  SCM signature = scm_cdr (get_signature ());
+
+  // In order to keep the loop structure and particularly the handling
+  // of terminating conditions reasonably straightforward and avoid
+  // scattering the code around, we don't use a separate loop when
+  // skipping optional arguments.  Instead we use "skipping" to
+  // indicate whether we are currently filling in optional arguments
+  // from their defaults.
+  bool skipping = false;
+
+  // The main loop just processes the signature in sequence, and the
+  // resulting actual arguments are accumulated in reverse order in args
+
+  SCM args = SCM_EOL;
+
+  for (; scm_is_pair (signature); signature = scm_cdr (signature))
+    {
+      SCM pred = scm_car (signature);
+
+      if (scm_is_pair (pred))
+        {
+          // If the predicate is not a function but a pair, it
+          // signifies an optional argument.  This is not quite the
+          // form declared to define-music-function (which is always
+          // a proper list) but a pair of predicate function and
+          // default value.
+
+          if (!skipping)
+            {
+              if (!scm_is_pair (rest))
+                scm_wrong_num_args (self_scm ());
+
+              SCM arg = scm_car (rest);
+              if (scm_is_true (scm_call_1 (scm_car (pred), arg)))
+                {
+                  args = scm_cons (arg, args);
+                  rest = scm_cdr (rest);
+                  continue;
+                }
+              skipping = true;
+              // Remove at most one tentative "\default"
+              if (scm_is_eq (SCM_UNSPECIFIED, arg))
+                rest = scm_cdr (rest);
+            }
+          args = scm_cons (with_loc (scm_cdr (pred), location), args);
+          continue;
+        }
+
+      // We have a mandatory argument here.
+      skipping = false;
+
+      if (!scm_is_pair (rest))
+        scm_wrong_num_args (self_scm ());
+
+      SCM arg = scm_car (rest);
+      rest = scm_cdr (rest);
+      args = scm_cons (arg, args);
+
+      if (scm_is_false (scm_call_1 (pred, arg)))
+        {
+          scm_apply_0 (ly_lily_module_constant ("argument-error"),
+                       scm_list_5 (parser, location,
+                                   scm_from_int (scm_ilength (args)),
+                                   pred, arg));
+          SCM val = scm_car (get_signature ());
+          val = scm_is_pair (val) ? scm_cdr (val) : SCM_BOOL_F;
+          return with_loc (val, location);
+        }
+    }
+
+  if (scm_is_pair (rest))
+    scm_wrong_num_args (self_scm ());
+
+  SCM res = scm_apply_0 (get_function (), scm_reverse_x (args, SCM_EOL));
+
+  SCM pred = scm_car (get_signature ());
+  // The return type predicate may have the form of a pair in which
+  // the car is the actual predicate and the cdr is the surrogate
+  // return value in the error case, to be extracted by
+  // music-function-call-error.
+  if (scm_is_pair (pred))
+    pred = scm_car (pred);
+
+  if (scm_is_true (scm_call_1 (pred, res)))
+    return with_loc (res, location, false);
+
+  return scm_call_4 (ly_lily_module_constant ("music-function-call-error"),
+                     parser, location,
+                     self_scm (), res);
+}