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docs: update interpreter

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Ilkka Seppälä
2024-05-26 13:34:46 +03:00
parent d991970439
commit b5d280e4f5
1 changed files with 63 additions and 36 deletions
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interpreter/README.md
+63 -36
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@@ -99,50 +99,77 @@ public class PlusExpression extends Expression {
Now, we are able to show the interpreter pattern in action parsing some simple math.
```java
// the halfling kids are learning some basic math at school
// define the math string we want to parse
final var tokenString="4 3 2 - 1 + *";
@Slf4j
public class App {
// the stack holds the parsed expressions
var stack = new Stack<Expression>();
public static void main(String[] args) {
// tokenize the string and go through them one by one
var tokenList = tokenString.split(" ");
for (var s : tokenList) {
if(isOperator(s)) {
// when an operator is encountered we expect that the numbers can be popped from the top of
// the stack
var rightExpression = stack.pop();
var leftExpression = stack.pop();
LOGGER.info("popped from stack left: {} right: {}", leftExpression.interpret(),rightExpression.interpret());
var operator = getOperatorInstance(s, leftExpression, rightExpression);
LOGGER.info("operator: {}", operator);
var result = operator.interpret();
// the operation result is pushed on top of the stack
var resultExpression = new NumberExpression(result);
stack.push(resultExpression);
LOGGER.info("push result to stack: {}", resultExpression.interpret());
} else {
// numbers are pushed on top of the stack
var i = new NumberExpression(s);
stack.push(i);
LOGGER.info("push to stack: {}", i.interpret());
// the halfling kids are learning some basic math at school
// define the math string we want to parse
final var tokenString = "4 3 2 - 1 + *";
// the stack holds the parsed expressions
var stack = new Stack<Expression>();
// tokenize the string and go through them one by one
var tokenList = tokenString.split(" ");
for (var s : tokenList) {
if (isOperator(s)) {
// when an operator is encountered we expect that the numbers can be popped from the top of
// the stack
var rightExpression = stack.pop();
var leftExpression = stack.pop();
LOGGER.info("popped from stack left: {} right: {}",
leftExpression.interpret(), rightExpression.interpret());
var operator = getOperatorInstance(s, leftExpression, rightExpression);
LOGGER.info("operator: {}", operator);
var result = operator.interpret();
// the operation result is pushed on top of the stack
var resultExpression = new NumberExpression(result);
stack.push(resultExpression);
LOGGER.info("push result to stack: {}", resultExpression.interpret());
} else {
// numbers are pushed on top of the stack
var i = new NumberExpression(s);
stack.push(i);
LOGGER.info("push to stack: {}", i.interpret());
}
}
// in the end, the final result lies on top of the stack
LOGGER.info("result: {}", stack.pop().interpret());
}
public static boolean isOperator(String s) {
return s.equals("+") || s.equals("-") || s.equals("*");
}
public static Expression getOperatorInstance(String s, Expression left, Expression right) {
return switch (s) {
case "+" -> new PlusExpression(left, right);
case "-" -> new MinusExpression(left, right);
default -> new MultiplyExpression(left, right);
};
}
}
// in the end, the final result lies on top of the stack
LOGGER.info("result: {}",stack.pop().interpret());
```
```
Executing the program produces the following console output.
```
popped from stack left: 1 right: 1
operator: +
push result to stack: 2
popped from stack left: 4 right: 2
operator: *
push result to stack: 8
result: 8
13:33:15.437 [main] INFO com.iluwatar.interpreter.App -- push to stack: 4
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- push to stack: 3
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- push to stack: 2
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- popped from stack left: 3 right: 2
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- operator: -
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- push result to stack: 1
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- push to stack: 1
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- popped from stack left: 1 right: 1
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- operator: +
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- push result to stack: 2
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- popped from stack left: 4 right: 2
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- operator: *
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- push result to stack: 8
13:33:15.440 [main] INFO com.iluwatar.interpreter.App -- result: 8
```
## Class diagram