-- Copyright Anton Ekblad 2012-2013
--
-- All rights reserved.
--
-- Redistribution and use in source and binary forms, with or without
-- modification, are permitted provided that the following conditions are met:
--
--     * Redistributions of source code must retain the above copyright
--       notice, this list of conditions and the following disclaimer.
--
--     * Redistributions in binary form must reproduce the above
--       copyright notice, this list of conditions and the following
--       disclaimer in the documentation and/or other materials provided
--       with the distribution.
--
--     * Neither the name of Anton Ekblad nor the names of other
--       contributors may be used to endorse or promote products derived
--       from this software without specific prior written permission.
--
-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-- "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-- LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-- A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-- OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-- SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-- LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-- DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-- THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-- (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-- OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

import Haste

main = withElems ["a","b","op","result"] calculator

calculator [a,b,op,result] = do
    onEvent a  OnKeyUp $ \_ -> recalculate
    onEvent b  OnKeyUp $ \_ -> recalculate
    onEvent op OnChange $ recalculate
  where
    recalculate = do
      ma <- getValue a
      mb <- getValue b
      Just op' <- getValue op
      case (ma, mb) of
        (Just a', Just b') -> setProp result "innerHTML" (toString $ calc op' a' b')
        _                  -> return ()

    calc "+" = (+)
    calc "-" = (-)
    calc "*" = (*)
    calc "/" = (/)
    calc _   = \_ _ -> 0 :: Double