1 | using System;
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2 | using System.Collections.Generic;
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3 | using System.Diagnostics.Eventing.Reader;
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4 | using System.Linq;
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5 | using System.Runtime.Remoting.Messaging;
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6 | using System.Text;
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7 | using System.Threading.Tasks;
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8 |
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9 | namespace HeuristicLab.Problems.GrammaticalOptimization {
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10 | public class ExpressionInterpreter {
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11 | private string sentence;
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12 | private int syIdx;
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13 | // interprets sentences from L(G(Expr)):
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14 | // Expr -> Term { ('+' | '-' | '^' ) Term }
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15 | // Term -> Fact { ('*' | '/') Fact }
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16 | // Fact -> '!' Expr | '(' Expr ')' | Var
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17 | // Var -> 'a'..'z'
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18 |
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19 | // for boolean problems the symbol * representes the AND operator, the symbol + represents the OR operator, ! = NOT, ^ = XOR
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20 |
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21 | public bool Interpret(string sentence, bool[] vars) {
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22 | InitLex(sentence);
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23 | var d = new double[vars.Length];
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24 | for (int i = 0; i < vars.Length; i++) d[i] = vars[i] ? 1.0 : 0.0;
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25 | return !(Expr(d).IsAlmost(0));
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26 | }
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27 |
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28 | public double Interpret(string sentence, double[] vars) {
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29 | InitLex(sentence);
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30 | return Expr(vars);
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31 | }
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32 |
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33 |
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34 | private void InitLex(string sentence) {
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35 | this.sentence = sentence;
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36 | this.syIdx = 0;
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37 | }
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38 |
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39 | private char CurSy() {
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40 | if (syIdx >= sentence.Length) return '\0';
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41 | return sentence[syIdx];
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42 | }
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43 | private void NewSy() {
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44 | if (syIdx < sentence.Length) syIdx++;
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45 | }
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46 |
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47 | // helper for xor
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48 | private double Not(double x) {
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49 | return x.IsAlmost(0) ? 1.0 : 0.0;
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50 | }
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51 |
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52 | private double Expr(double[] d) {
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53 | var r = 0.0;
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54 | r = Term(d);
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55 | while (CurSy() == '+' || CurSy() == '-' || CurSy() == '^') {
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56 | if (CurSy() == '+') {
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57 | NewSy();
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58 | r += Expr(d);
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59 | } else if (CurSy() == '-') {
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60 | NewSy();
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61 | r -= Expr(d);
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62 | } else if (CurSy() == '^') {
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63 | NewSy();
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64 | var e = Expr(d);
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65 | r = Not(r) * e + r * Not(e); // xor = (!x AND y) OR (x AND !y)
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66 | }
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67 | }
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68 | return r;
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69 | }
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70 |
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71 | private double Term(double[] d) {
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72 | var r = 0.0;
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73 | r = Fact(d);
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74 | while (CurSy() == '*' || CurSy() == '/') {
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75 | if (CurSy() == '*') {
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76 | NewSy();
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77 | r *= Term(d);
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78 | } else if (CurSy() == '/') {
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79 | NewSy();
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80 | r /= Term(d);
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81 | }
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82 | }
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83 | return r;
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84 | }
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85 |
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86 | private double Fact(double[] d) {
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87 | double r = 0.0;
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88 | if (CurSy() == '!') {
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89 | NewSy();
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90 | r = Not(Expr(d));
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91 | } else if (CurSy() == '(') {
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92 | NewSy();
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93 | r = Expr(d);
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94 | if (CurSy() != ')') throw new ArgumentException();
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95 | NewSy();
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96 | } else if (CurSy() >= 'a' && CurSy() <= 'z') {
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97 | int o = Convert.ToByte(CurSy()) - Convert.ToByte('a');
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98 | if (o < 0 || o >= d.Length) throw new ArgumentException();
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99 | r = d[o];
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100 | NewSy();
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101 | } else throw new ArgumentException();
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102 | return r;
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103 | }
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104 |
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105 | }
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106 | }
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