Added support for the ternary if/else form

compiler.rb

@@ -17,7 +17,7 @@ class Compiler
   # a special calling convention
   @@keywords = Set[
                    :do, :class, :defun, :if, :lambda,
-                   :assign, :while, :index, :let, :case
+                   :assign, :while, :index, :let, :case, :ternif
                   ]
 
 
@@ -173,14 +173,27 @@ def compile_if(scope, cond, if_arm, else_arm = nil)
     l_else_arm = @e.get_local
     l_end_if_arm = @e.get_local
     @e.jmp_on_false(l_else_arm)
-    compile_eval_arg(scope, if_arm)
+   compile_eval_arg(scope, if_arm)
     @e.jmp(l_end_if_arm) if else_arm
     @e.local(l_else_arm)
     compile_eval_arg(scope, else_arm) if else_arm
     @e.local(l_end_if_arm) if else_arm
     return [:subexpr]
   end
 
+  # Compiles the ternary if form (cond ? then : else) 
+  # It may be better to transform this into the normal
+  # if form in the tree.
+  def compile_ternif(scope, cond, alt)
+    if alt.is_a?(Array) && alt[0] == :ternalt
+      if_arm = alt[1]
+      else_arm = alt[2]
+    else
+      if_arm = alt
+    end
+    compile_if(scope,cond,if_arm,else_arm)
+  end
+
   def compile_case(scope, *args)
 #    error(":case not implemented yet", scope, [:case]+args)
     # FIXME: