From 2eda0f6d07ddb3cacc3a4b78728019d5de26cb90 Mon Sep 17 00:00:00 2001
From: Phil Hagelberg <technomancy@gmail.com>
Date: Fri, 7 Nov 2008 22:57:05 -0800
Subject: [PATCH] Whoa; I just implemented quasiquote. That was way too easy.

---
 lib/bus_scheme/eval.rb       | 12 ++++++++++++
 lib/bus_scheme/primitives.rb |  7 ++-----
 test/test_eval.rb            |  5 +++++
 3 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/lib/bus_scheme/eval.rb b/lib/bus_scheme/eval.rb
index 816d115..69f6daf 100644
--- a/lib/bus_scheme/eval.rb
+++ b/lib/bus_scheme/eval.rb
@@ -55,4 +55,16 @@ def stacktrace
   def stack
     @@stack
   end
+
+  # TODO: unquote-splicing
+  def quasiquote(arg)
+    if !arg.is_a? Cons or arg.empty?
+      arg
+    elsif arg.is_a? Cons and arg.car == 'unquote'.sym
+      eval(arg.cadr)
+    else
+      Cons.new(quasiquote(arg.car),
+               quasiquote(arg.cdr))
+    end
+  end
 end
diff --git a/lib/bus_scheme/primitives.rb b/lib/bus_scheme/primitives.rb
index 9357c15..c8a7e33 100644
--- a/lib/bus_scheme/primitives.rb
+++ b/lib/bus_scheme/primitives.rb
@@ -43,11 +43,8 @@ def self.special_form(identifier, value)
   define 'exit', primitive { exit }
   define 'quit', BusScheme['exit'.sym]
 
-
-  # TODO: write
-  special_form 'quasiquote', primitive { }
-  special_form 'unquote', primitive { }
-  special_form 'unquote-splicing', primitive { }
+  special_form 'quasiquote', primitive { |arg| quasiquote(arg) }
+  special_form 'qq', BusScheme['quasiquote'.sym]
 
   # Primitives that can't be defined in terms of other forms:
   special_form 'quote', primitive { |arg| arg }
diff --git a/test/test_eval.rb b/test/test_eval.rb
index 0dd1bfe..ce55661 100644
--- a/test/test_eval.rb
+++ b/test/test_eval.rb
@@ -87,6 +87,11 @@ def test_evals_string_ending_in_comment
                         ;; should be four"
   end
 
+  def test_quasi_quote
+    assert_evals_to([:hey.sym, :there.sym, "dude"].to_list,
+                    '(qq (hey there (unquote (+ "du" "de"))))')
+  end
+
 #   def test_tail_call_optimization
 #     Timeout.timeout(1) do
 #       assert_nothing_raised { eval "((lambda (x) (x x)) (lambda (x) (x x)))" }