<br />
<b>Deprecated</b>:  The each() function is deprecated. This message will be suppressed on further calls in <b>/home/zhenxiangba/zhenxiangba.com/public_html/phproxy-improved-master/index.php</b> on line <b>456</b><br />
-- Application of the deep selection patterns
-- Michael and Sergio
-- Mon Apr 18 15:47:00 PDT 2011

-- Examples:
--  1.  Find all the vairable of an expression
--  2.  Find some common subexpression of an expressio

import SetFunctions

data Exp = Lit Int
         | Var [Char]
         | Add Exp Exp
         | Mul Exp Exp

-- return expressions with a given subexpression
withSub exp = exp
            ? op (withSub exp) unknown
            ? op unknown (withSub exp)
 where op = Add ? Mul

-- Examples:
exp1 = Add (Mul (Lit 42) (Add (Lit 0) (Var "z")))
           (Add (Var "x") (Var "y"))
exp2 = Add (Mul (Lit 42) (Add (Lit 42) (Var "y")))
           (Add (Var "x") (Var "y"))

-- get some variable occurring in an expression
varOf (withSub (Var v)) = v

-- get the set of the variables (identifiers) of an expression
allVariablesOf exp = sortValues (set1 varOf exp)

test = allVariablesOf exp1

-- Problem: finding common subexpressions in an expression:

-- Define all expressions containing a common subexpressions:
withCommonSub e = op (withCommonSub e) unknown
                   ? op unknown (withCommonSub e)
                   ? op (withSub e) (withSub e)
  where op = Add ? Mul

-- Finding common subexpressions is straightforward:
commonSub (withCommonSub e) = e

-- all the common subexpressions
ctest1 = set1 commonSub exp1
ctest2 = set1 commonSub exp2