Data commit

Task/Amb/Ruby/amb.rb

@@ -0,0 +1,49 @@
+require "continuation"
+
+class Amb
+  class ExhaustedError < RuntimeError; end
+
+  def initialize
+    @fail = proc { fail ExhaustedError, "amb tree exhausted" }
+  end
+
+  def choose(*choices)
+    prev_fail = @fail
+    callcc { |sk|
+      choices.each { |choice|
+	callcc { |fk|
+	  @fail = proc {
+	    @fail = prev_fail
+	    fk.call(:fail)
+	  }
+	  if choice.respond_to? :call
+	    sk.call(choice.call)
+	  else
+	    sk.call(choice)
+	  end
+	}
+      }
+      @fail.call
+    }
+  end
+
+  def failure
+    choose
+  end
+
+  def assert(cond)
+    failure unless cond
+  end
+end
+
+A = Amb.new
+w1 = A.choose("the", "that", "a")
+w2 = A.choose("frog", "elephant", "thing")
+w3 = A.choose("walked", "treaded", "grows")
+w4 = A.choose("slowly", "quickly")
+
+A.choose() unless w1[-1] == w2[0]
+A.choose() unless w2[-1] == w3[0]
+A.choose() unless w3[-1] == w4[0]
+
+puts w1, w2, w3, w4