progs/app06.scala
author Christian Urban <christian dot urban at kcl dot ac dot uk>
Tue, 18 Oct 2016 10:43:26 +0100
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def simp(r: Rexp): (Rexp, Val => Val) = r match {
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  case SEQ(r1, r2) => {
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    val (r1s, f1s) = simp(r1)
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    val (r2s, f2s) = simp(r2)
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    (r1s, r2s) match {
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      case (ZERO, _) => (ZERO, F_ERROR)
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      case (_, ZERO) => (ZERO, F_ERROR)
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      case (ONE, _) => (r2s, F_SEQ_Void1(f1s, f2s))
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      case (_, ONE) => (r1s, F_SEQ_Void2(f1s, f2s))
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      case _ => (SEQ(r1s,r2s), F_SEQ(f1s, f2s))
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    }
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  }
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  ...
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def F_SEQ_Void1(f1: Val => Val, f2: Val => Val) = 
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  (v:Val) => Sequ(f1(Void), f2(v))
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def F_SEQ_Void2(f1: Val => Val, f2: Val => Val) = 
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  (v:Val) => Sequ(f1(v), f2(Void))
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def F_SEQ(f1: Val => Val, f2: Val => Val) = 
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  (v:Val) => v match {
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    case Sequ(v1, v2) => Sequ(f1(v1), f2(v2)) }