/README.md

# Parenj: The Paren Programming Language written in Java #



(C) 2013 Kim, Taegyoon



Paren is a dialect of Lisp. It is designed to be an embedded language. You can use Java in your Paren program.



## Compile ##

```

cd src

javac paren.java parenj.java

```



## Run ##

```

Usage: java parenj [OPTIONS...] [FILES...]



OPTIONS:

    -h    print this screen.

    -v    print version.

```



## Reference ##

```

Predefined Symbols:

 ! != % && * + ++ - -- .

 .get .set / < <= = == > >= E

 PI ^ apply begin ceil char-at chr dec double eval

 exit false filter floor fn fold for if inc int

 length list ln log10 map new nth null pr prn

 quote rand range read-string set sqrt strcat string strlen system

 true type when while ||

Etc.:

 (list) "string" ; end-of-line comment

```



## Files ##

* paren.java: Paren language library

* parenj.java: Paren REPL executable



## Examples ##

### Hello, World! ###

```

(prn "Hello, World!")

```



### Function ###



In a function, [lexical scoping](http://en.wikipedia.org/wiki/Lexical_scoping#Lexical_scoping) is used.



```

> ((fn (x y) (+ x y)) 1 2)

3 : java.lang.Integer

> ((fn (x) (* x 2)) 3)

6 : java.lang.Integer

> (set sum (fn (x y) (+ x y)))

 : null

> (sum 1 2)

3 : java.lang.Integer

> (fold sum (range 1 10 1))

55 : java.lang.Integer

> (set even? (fn (x) (== 0 (% x 2))))

 : null

> (even? 3)

false : java.lang.Boolean

> (even? 4)

true : java.lang.Boolean

> (apply + (list 1 2 3))

6 : java.lang.Integer

> (map sqrt (list 1 2 3 4))

[1.0, 1.4142135623730951, 1.7320508075688772, 2.0] : java.util.Vector

> (filter even? (list 1 2 3 4 5))

[2, 4] : java.util.Vector

> (= "abc" "abc") ; Object.equals()

true : java.lang.Boolean

> (set x 1)

  ((fn (x) (prn x) (set x 3) (prn x)) 4) ; lexical scoping

  x    

4

3

1 : java.lang.Integer

> (set adder (fn (amount) (fn (x) (+ x amount)))) ; lexical scoping

  (set add3 (adder 3))

  (add3 4)    

7 : java.lang.Integer

```



#### Recursion ####

```

> (set factorial (fn (x) (if (<= x 1) x (* x (factorial (dec x))))))

  (for i 1 5 1 (prn i (factorial i)))

1 1

2 2

3 6

4 24

5 120

 : null

```



### List ###

```

> (nth 1 (list 2 4 6))

4 : java.lang.Integer

> (length (list 1 2 3))

3 : java.lang.Integer

```



### Java interoperability (from Paren) ###

```

> (. java.lang.Math random) ; class's static method

0.4780254852371699 : java.lang.Double

> (. java.lang.Math floor 1.5)

1.0 : java.lang.Double

> (. "abc" length) ; object's method

3 : java.lang.Integer

> (. true toString)

true : java.lang.String

> (set i 3)

 : null

> (. i doubleValue)

3.0 : java.lang.Double

> (.get java.lang.Math PI) ; get field

3.141592653589793 : java.lang.Double

> (.get parenj testField)

 : null

> (.set parenj testField 1) ; set field

  (.get parenj testField)

1 : java.lang.Integer

> (.set parenj testField "abc")

  (.get parenj testField)

abc : java.lang.String

> (. (new java.math.BigInteger "2") pow 100) ; 2 ^ 100

1267650600228229401496703205376 : java.math.BigInteger

```



### Java interoperability (from Java) ###

player.java

```

public class player {

    private int life;

    public int getLife() {

        return life;

    }

    public void setLife(int life) {

        this.life = life;

    }

}

```



parenjTest.java

```

public class parenjTest {

    public static Object testField;

    public static void main(String[] args) {

        paren p = new paren();

        player pl = new player();

        

        // Method 1: using class's field

        testField = pl;

        p.eval_string("(set pl (.get parenjTest testField))");

        p.eval_string("(. pl setLife 100)");

        System.out.println(p.eval_string("(. pl getLife)").intValue());

        

        // Method 2: not using class's field, set variable to Java's local variable

        p.global_env.env.put("pl2", new paren.node(pl));

        p.eval_string("(. pl2 setLife 200)");

        System.out.println(p.eval_string("(. pl2 getLife)").intValue());

        p.global_env.env.remove("p12"); // remove variable

    }

}



```



### System Command ###

```

(system "notepad" "a.txt")

```



### [Project Euler Problem 1](http://projecteuler.net/problem=1) ###

```

(set s 0)

(for i 1 999 1

    (when (|| (== 0 (% i 3)) (== 0 (% i 5)))

        (set s (+ s i))))

(prn s)

```

=> 233168



```

(apply + (filter (fn (x) (|| (== 0 (% x 3)) (== 0 (% x 5)))) (range 1 999 1)))

```

=> 233168



### [Project Euler Problem 2](http://projecteuler.net/problem=2) ###

```

(set a 1)

(set b 1)

(set sum 0)

(while (<= a 4000000)

  (set c (+ a b))

  (set a b)

  (set b c)

  (when (== 0 (% a 2))

    (set sum (+ sum a))))

(prn sum)

```

=> 4613732



### [Project Euler Problem 4](http://projecteuler.net/problem=4) ###

```

(set maxP 0)

(for i 100 999 1

  (for j 100 999 1	

    (set p (* i j))

    (set ps (string p))

    (set len (strlen ps))

    (set to (/ len 2))

    (set pal true)

    (set k 0)

    (set k2 (dec len))

    (while

      (&& (< k to) pal)

	  (when (!= (char-at ps k) (char-at ps k2))

		(set pal false))

	  (++ k)

	  (-- k2))

	(when pal

	  (when (> p maxP)

		(set maxP p)))))

(prn maxP)

```

=> 906609



[More solutions of Project Euler in Paren](https://bitbucket.org/ktg/euler-paren)



### [99 Bottles of Beer](http://en.wikipedia.org/wiki/99_Bottles_of_Beer) ###

```

(for i 99 1 -1

  (prn i "bottles of beer on the wall," i "bottles of beer.")

  (prn "Take one down and pass it around," (dec i) "bottle of beer on the wall."))

```



## Alternative Implementations ##

* [Paren](https://bitbucket.org/ktg/paren) (Paren running natively)

* [Parenj](https://bitbucket.org/ktg/parenj) (Paren running on the Java Virtual Machine)

* [Parenjs](https://bitbucket.org/ktg/parenjs) (Paren compiler targeting JavaScript)



## License ##



   Copyright 2013 Kim, Taegyoon



   Licensed under the Apache License, Version 2.0 (the "License");

   you may not use this file except in compliance with the License.

   You may obtain a copy of the License at



   [http://www.apache.org/licenses/LICENSE-2.0](http://www.apache.org/licenses/LICENSE-2.0)



   Unless required by applicable law or agreed to in writing, software

   distributed under the License is distributed on an "AS IS" BASIS,

   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

   See the License for the specific language governing permissions and

   limitations under the License.