1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
|
package bjc.utils.parserutils;
import java.util.Deque;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.function.Function;
import bjc.utils.data.IPrecedent;
import bjc.utils.funcdata.FunctionalList;
/**
* Utility to run the shunting yard algorithm on a bunch of tokens
*
* @author ben
*
* @param <E>
* The type of tokens being shunted
*/
public class ShuntingYard<E> {
/**
* A enum representing the fundamental operator types
*
* @author ben
*
*/
public static enum Operator implements IPrecedent {
/**
* Represents addition
*/
ADD(1),
/**
* Represents division
*/
DIVIDE(4),
/**
* Represents multiplication
*/
MULTIPLY(3),
/**
* Represents subtraction
*/
SUBTRACT(2);
private final int precedence;
private Operator(int p) {
precedence = p;
}
/*
* (non-Javadoc)
*
* @see bjc.utils.parserutils.IPrecedent#getPrecedence()
*/
@Override
public int getPrecedence() {
return precedence;
}
}
/**
* Holds all the shuntable operations
*/
private Map<String, IPrecedent> ops;
/**
* Create a new shunting yard with a default set of operators
*/
public ShuntingYard() {
ops = new HashMap<>();
ops.put("+", Operator.ADD);
ops.put("-", Operator.SUBTRACT);
ops.put("*", Operator.MULTIPLY);
ops.put("/", Operator.DIVIDE);
}
/**
* Add an operator to the list of shuntable operators
*
* @param tok
* The token representing the operator
* @param i The precedence of the operator to add
*/
public void addOp(String tok, int i) {
this.addOp(tok, IPrecedent.newSimplePrecedent(i));
}
/**
* Add an operator to the list of shuntable operators
*
* @param tok
* The token representing the operator
* @param prec
* The precedence of the operator
*/
public void addOp(String tok, IPrecedent prec) {
ops.put(tok, prec);
}
private boolean isHigherPrec(String op, String sub) {
return (ops.containsKey(sub) && ops.get(sub).getPrecedence() >= ops
.get(op).getPrecedence());
}
/**
* Transform a string of tokens from infix notation to postfix
*
* @param inp
* The string to transform
* @param transform
* The function to use to transform strings to tokens
* @return A list of tokens in postfix notation
*/
public FunctionalList<E> postfix(FunctionalList<String> inp,
Function<String, E> transform) {
FunctionalList<E> outp = new FunctionalList<>();
Deque<String> stack = new LinkedList<>();
inp.forEach((token) -> {
if (ops.containsKey(token)) {
while (!stack.isEmpty()
&& isHigherPrec(token, stack.peek())) {
outp.add(transform.apply(stack.pop()));
}
stack.push(token);
} else if (token.equals("(")) {
stack.push(token);
} else if (token.equals(")")) {
while (!stack.peek().equals("(")) {
outp.add(transform.apply(stack.pop()));
}
stack.pop();
} else {
outp.add(transform.apply(token));
}
});
while (!stack.isEmpty()) {
outp.add(transform.apply(stack.pop()));
}
return outp;
}
/**
* Remove an operator from the list of shuntable operators
*
* @param tok
* The token representing the operator
*/
public void removeOp(String tok) {
ops.remove(tok);
}
}
|
