From d138b2e91c5752d332b4e07017c82e3c0396836b Mon Sep 17 00:00:00 2001
From: Paul Mucur <mudge@mudge.name>
Date: Sun, 14 Jun 2015 17:20:53 +0100
Subject: [PATCH 1/3] proc.c: Implement Proc#* for Proc composition

* proc.c (proc_compose): Implement Proc#* for Proc composition, enabling
  composition of Procs and Methods. [Feature #6284]

* test/ruby/test_proc.rb: Add test cases for Proc composition.
---
 proc.c                 | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++
 test/ruby/test_proc.rb | 51 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 105 insertions(+)

diff --git a/proc.c b/proc.c
index 6d153c1..c73fcf1 100644
--- a/proc.c
+++ b/proc.c
@@ -2818,6 +2818,59 @@ rb_method_curry(int argc, const VALUE *argv, VALUE self)
     return proc_curry(argc, argv, proc);
 }
 
+static VALUE
+compose(VALUE dummy, VALUE args, int argc, VALUE *argv, VALUE passed_proc)
+{
+    VALUE f, g, fargs;
+    f = RARRAY_AREF(args, 0);
+    g = RARRAY_AREF(args, 1);
+    fargs = rb_ary_new3(1, rb_proc_call_with_block(g, argc, argv, passed_proc));
+
+    return rb_proc_call(f, fargs);
+}
+
+ /*
+  *  call-seq:
+  *     prc * g -> a_proc
+  *
+  *  Returns a proc that is the composition of this proc and the given proc <i>g</i>.
+  *  The returned proc takes a variable number of arguments, calls <i>g</i> with them
+  *  then calls this proc with the result.
+  *
+  *     f = proc {|x| x * 2 }
+  *     g = proc {|x, y| x + y }
+  *     h = f * g
+  *     p h.call(1, 2) #=> 6
+  */
+static VALUE
+proc_compose(VALUE self, VALUE g)
+{
+    VALUE proc, args;
+    rb_proc_t *procp;
+    int is_lambda;
+
+    if (!rb_obj_is_method(g) && !rb_obj_is_proc(g)) {
+        rb_raise(rb_eTypeError,
+                "wrong argument type %s (expected Proc/Method)",
+                rb_obj_classname(g));
+    }
+
+    if (rb_obj_is_method(g)) {
+        g = method_to_proc(g);
+    }
+
+    args = rb_ary_new3(2, self, g);
+
+    GetProcPtr(self, procp);
+    is_lambda = procp->is_lambda;
+
+    proc = rb_proc_new(compose, args);
+    GetProcPtr(proc, procp);
+    procp->is_lambda = is_lambda;
+
+    return proc;
+}
+
 /*
  *  Document-class: LocalJumpError
  *
@@ -2906,6 +2959,7 @@ Init_Proc(void)
     rb_define_method(rb_cProc, "lambda?", rb_proc_lambda_p, 0);
     rb_define_method(rb_cProc, "binding", proc_binding, 0);
     rb_define_method(rb_cProc, "curry", proc_curry, -1);
+    rb_define_method(rb_cProc, "*", proc_compose, 1);
     rb_define_method(rb_cProc, "source_location", rb_proc_location, 0);
     rb_define_method(rb_cProc, "parameters", rb_proc_parameters, 0);
 
diff --git a/test/ruby/test_proc.rb b/test/ruby/test_proc.rb
index b67773b..a6e9bcc 100644
--- a/test/ruby/test_proc.rb
+++ b/test/ruby/test_proc.rb
@@ -1341,4 +1341,55 @@ def g
       e.each {}
     EOS
   end
+
+  def test_compose
+    f = proc{|x| x * 2}
+    g = proc{|x| x + 1}
+    h = f * g
+
+    assert_equal(6, h.call(2))
+  end
+
+  def test_compose_with_multiple_args
+    f = proc{|x| x * 2}
+    g = proc{|x, y| x + y}
+    h = f * g
+
+    assert_equal(6, h.call(1, 2))
+  end
+
+  def test_compose_with_block
+    f = proc{|x| x * 2}
+    g = proc{|&blk| blk.call(1) }
+    h = f * g
+
+    assert_equal(8, h.call { |x| x + 3 })
+  end
+
+  def test_compose_with_lambda
+    f = lambda{|x| x * 2}
+    g = lambda{|x| x}
+    h = f * g
+
+    assert(h.lambda?)
+  end
+
+  def test_compose_with_method
+    f = proc{|x| x * 2}
+    c = Class.new {
+      def g(x) x + 1 end
+    }
+    g = c.new.method(:g)
+    h = f * g
+
+    assert_equal(6, h.call(2))
+  end
+
+  def test_compose_with_nonproc_or_method
+    f = proc{|x| x * 2}
+
+    assert_raise(TypeError) {
+      f * 5
+    }
+  end
 end
-- 
2.6.4