Curta

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A small, customizable expression evaluator.

Curta 최신버젼 다운로드

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## Curta &nbsp; [![Build Status](https://travis-ci.org/bkiers/Curta.png)](https://travis-ci.org/bkiers/Curta) [![Release](https://img.shields.io/github/release/bkiers/Curta.svg?label=maven version)](https://jitpack.io/#bkiers/Curta)

A small, customizable expression evaluator. Named after the [mechanical calculator
introduced by Curt Herzstark](http://en.wikipedia.org/wiki/Curta) in 1948.

The parser is generated using [JavaCC](http://javacc.java.net). The generated parser 
classes are *not* a part of this repository, only [the grammar](https://github.com/bkiers/Curta/blob/master/src/main/jjtree/CurtaParser.jjt)
is included. The parser source files are being generated by Maven.

It supports all static methods, and variables, from 
[Java 7's Math class](http://docs.oracle.com/javase/7/docs/api/java/lang/Math.html) 
and can be easily extended with extra functions. Even certain expressions can be 
programmatically changed. For example, changing the meaning of the `^` as a binary
XOR operator to act as a power operator (see [Changing expressions](#changing-expressions)
below).

## Installation

### Gradle

Add the repository:

```groovy
repositories {
  maven {
    url "https://jitpack.io"
  }
}
```

and then add the dependency:

```groovy
dependencies {
  compile 'com.github.bkiers:Curta:1.0.0'
}
```

### Maven

Add the following to your POM's `<repositories>` tag:

```xml
<repository>
 <id>jitpack.io</id>
 <url>https://jitpack.io</url>
</repository>
```

then add the following dependency:

```xml
<dependency>
 <groupId>com.github.bkiers</groupId>
 <artifactId>Curta</artifactId>
 <version>1.0.0</version>
</dependency>
```

Or clone this repository and run: `mvn install` which will create a JAR of Curta
in your local Maven repository, as well as in the project's `target/` folder.

## Quick demo

For a more thorough explanation of this library, scroll to [the next paragraph](#data-types), 
but for the impatient, here's a quick demo of how to use *Curta*:

```java
Curta curta = new Curta();

// logical
assertEquals( curta.eval("false || true"), true );
assertEquals( curta.eval("(true || false) && true"), true );

// equality
assertEquals( curta.eval("1 == 1.0"), true );
assertEquals( curta.eval("1 != 0.99999"), true );

// relational
assertEquals( curta.eval("-1 < -0.99999"), true );
assertEquals( curta.eval("1 <= 0.99999"), false );

// binary
assertEquals( curta.eval("~8"), -9L );
assertEquals( curta.eval("4 << 1"), 8L );

// basic arithmetic
assertEquals( curta.eval("1 + 2 * 3"), 7.0 );
assertEquals( curta.eval("(1 + 2) * 3"), 9.0 );

// variables
curta.addVariable("mu", 42);
assertEquals( curta.eval("mu + mu"), 84.0 );
assertEquals( curta.eval("return mu + mu"), 84.0 );
assertEquals( curta.eval("foo = 2; mu + foo"), 44.0 );

// built-in functions
assertEquals( curta.eval("abs(-999)"), 999.0 );
assertEquals( curta.eval("cos(PI)"), -1.0 );
assertEquals( curta.eval("hypot(3, 4)"), 5.0 );

// custom function
curta.addFunction(new Function("thrice") {
    @Override
    public Object eval(Object... params) {
        return super.getDouble(0, params) * 3;
    }
});
assertEquals( curta.eval("thrice(9)"), 27.0 );

// change existing expressions
curta.setExpression(Operator.Add, new Expression() {
 @Override
 public Object eval(CurtaNode ast,
 Map<String, Object> vars,
 Map<String, Function> functions,
 Map<Integer, Expression> expressions) {

// from now on N + M will become N * M
        return super.evalChildAsDouble(0, ast, vars, functions, expressions) *
                super.evalChildAsDouble(1, ast, vars, functions, expressions);
    }
});
assertEquals( curta.eval("3 + 5"), 15.0 );

// reset variables, functions and expressions
curta.clear();
assertEquals( curta.eval("3 + 5"), 8.0 );
```

## Data types

The following data types are supported:

* number (`double` and `long`)
* boolean (`true` and `false`)
* null (`null`)

## Operators

Below follows a list of all supported operators, starting with the ones with
the highest precedence.

1. grouped expressions: `(` ... `)`
2. power: `**`
3. bitwise not: `~`
4. 
 * unary minus: `-`
 * unary plus: `+`
 * not: `!`
5. 
 * multiply: `*`
 * division: `/`
 * modulus: `%`
6. 
 * add: `+`
 * subtract: `-`
7. 
 * signed left shift: `<<`
 * signed right shift: `>>`
 * unsigned right shift: `>>>`
8. 
 * less than: `<`
 * less than or equal: `<=`
 * greater than: `>`
 * greater than or equal: `>=`
9. 
 * equal: `==`
 * not equal: `!=`
10. bitwise AND: `&`
11. bitwise XOR: `^`
12. bitwise OR: `|`
13. AND: `&&`
14. OR: `||`

Note that binary expressions are *all* evaluated from left to right. This means
that an expression like 234, `2**3**4`, is evaluated as `(2**3)**4`. 
Use parenthesis to let it evaluate from right to left: `2**(3**4)`

## Variables

The variables `PI` and `E` from [Java 7's Math class](http://docs.oracle.com/javase/7/docs/api/java/lang/Math.html) 
are built-in, and you can assign variables yourself too, either programmatically, or in the input that
is to be evaluated. Some examples:

```java
Curta curta = new Curta();

System.out.println(curta.eval("PI"));
System.out.println(curta.eval("E"));

curta.addVariable("answer", 21);

System.out.println(curta.eval("answer * 2"));

System.out.println(curta.eval("x = 5; answer * x"));
```

which will print:

```
3.141592653589793
2.718281828459045
42.0
105.0
```

As you can see in the previous example, you can evaluate more than one statement/expression 
at the same time. The last expression is returned by `Curta`'s `eval(...)` method. You can
either evaluate `String`s, or `File`s. If you evaluate more than one statement/expression,
you need to separate them with a semi colon, `';'`, or a line break.

## Functions

#### Built-in functions

All methods from [Java 7's Math class](http://docs.oracle.com/javase/7/docs/api/java/lang/Math.html) 
are supported. However, there's no need to put `Math.` in front of it.

Some examples:

```java
Curta curta = new Curta();

System.out.println(curta.eval("sin(1)"));
System.out.println(curta.eval("random()"));
System.out.println(curta.eval("hypot(3, 4)"));
System.out.println(curta.eval("abs(-1)"));
System.out.println(curta.eval("min(42, -11)"));
```

would print:

```
0.8414709848078965
0.6805327383776745
5.0
1.0
-11.0
```

*(of course, the call to `random()` is most likely to result in something different... :))*

#### Custom functions

You can also define your own functions programmatically. For example, you would like
to create a function that will return `true` (or `false`) if a number is prime or not.

You can use `Curta`s `addFunction(Function)` method for this:

```java
Curta curta = new Curta();

curta.addFunction(new Function("isPrime") {

@Override
    public Object eval(Object... params) {

// number of parameters must be exactly 1 (min=1, max=1)
        super.checkNumberOfParams(1, 1, params);

// expecting an integer value (not floating-point!)
        long value = super.getLong(0, params);

// return whether this number is prime
        return new java.math.BigInteger(String.valueOf(value)).isProbablePrime(20);
    }
});

String expression = "isPrime(2147483647)";

System.out.printf("%s = %s\n", expression, curta.eval(expression));
```

which will print: `isPrime(2147483647) = true`

As you can see, the abstract class [`Function`](https://github.com/bkiers/Curta/blob/master/src/main/java/curta/function/Function.java),
which your custom function must be extended from, has a couple of utility methods 
to check the number of parameters, and convert these parameters to more usable 
classes (a `long`, in this case). This means that evaluating either `"isPrime(true)"`
or `"isPrime(11, 17)"` would result in an exception to be thrown.

## Changing expressions

Some expressions can be changed (or removed) from the parser programmatically. Let's say
you don't want to have support for the *bitwise-not* operator. You can then simply set the 
operator of an expression to `null`.

For example, the following code:

```java
Curta curta = new Curta();
System.out.println(curta.eval("~42"));
```

would print `-43`, but:

```java
Curta curta = new Curta();
curta.setExpression(Operator.BitNot, null);
System.out.println(curta.eval("~42"));
```
would throw the following exception:

`Exception in thread "main" java.lang.RuntimeException: not implemented: ~ (BitNot)`

One more example. Let's say you want to support `final` variables. Whenever a variable 
consists of only capital letters (or underscores), you don't want that variable to ever 
change. You could do this by overriding the default assignment-expression like this:

```java
Curta curta = new Curta();

curta.setExpression(Operator.Assign, new Expression() {
 @Override
 public Object eval(CurtaNode ast, Map<String, Object> vars, Map<String, Function> functions, Map<Integer, Expression> expressions) {

// get the text of the 1st child
        String id = super.getTextFromChild(0, ast);

// evaluate the 2nd child
        Object value = super.evalChild(1, ast, vars, functions, expressions);

// check if it's made from caps only, and is already defined
        if(id.matches("[A-Z_]+") && vars.containsKey(id)) {
            System.err.println("cannot reassign: " + id);
        }
        else {
            vars.put(id, value);
        }

return value;
    }
});

System.out.println(curta.eval("PI = 3; VAR = 42; VAR = -1; VAR"));
```

The code above will return `42` and causes the following to be printed to the `system.err`:

```
cannot reassign: PI
cannot reassign: VAR
```

Changing `VAR` to `var` will cause `-1` to be returned.

See the [`Operator` enum](https://github.com/bkiers/Curta/blob/master/src/main/java/nl/bigo/curta/Operator.java)
to find out which operators can be reassigned.

Calling `clear()` on the `Curta` instance will reset everything: the *bitwise-not* is supported 
again, and you can reassign capitalized variables.

Curta

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