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Paren: The Paren Programming Language

(C) 2013 Kim, Taegyoon

Paren is a dialect of Lisp. It is designed to be an embedded language.

Run

Usage: paren [OPTIONS...] [FILES...]

OPTIONS:
    -h    print this screen.
    -v    print version.

Reference

Predefined Symbols:
 ! != % && * + ++ - -- /
 < <= == > >= 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 nth 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

  • libparen.h libparen.cpp: Paren language library
  • paren.cpp: Paren REPL executable

Examples

Hello, World!

(prn "Hello, World!")

Function

In a function, lexical scoping is used.

> ((fn (x y) (+ x y)) 1 2)
3 : int
> ((fn (x) (* x 2)) 3)
6 : int
> (set sum (fn (x y) (+ x y)))
 : nil
> (sum 1 2)
3 : int
> (fold sum (range 1 10 1))
55 : int
> (set even? (fn (x) (== 0 (% x 2))))
 : nil
> (even? 3)
false : bool
> (even? 4)
true : bool
> (apply + (list 1 2 3))
6 : int
> (map sqrt (list 1 2 3 4))
(1 1.4142135623730951 1.7320508075688772 2) : list
> (filter even? (list 1 2 3 4 5))
(2 4) : list
> (set x 1) ((fn (x) (prn x) (set x 3) (prn x)) 4) (prn x) ; lexical scoping
4
3
1
 : nil
> (set adder (fn (amount) (fn (x) (+ x amount)))) (set add3 (adder 3)) (add3 4); lexical scoping
7 : int

Recursion

> (set factorial (fn (x) (if (<= x 1) x (* x (factorial (dec x))))))
 : nil
> (for i 1 5 1 (prn i (factorial i)))
1 1
2 2
3 6
4 24
5 120
 : nil

List

> (nth 1 (list 2 4 6))
4 : int
> (length (list 1 2 3))
3 : int

System Command (Shell)

(system "notepad" "a.txt") ; compatible with Parenj
(system "notepad a.txt") ; same as above; not compatible with Parenj

Embedding

Compile libparen.cpp

#include "libparen.h"

using namespace libparen;

int main() {
    paren p;    
    cout << p.eval_string("(+ 1 2)").v_int << endl; // evaluate code and get return value
    p.eval_string("(set a 1)"); // evaluate code
    cout << p.get("a").v_int << endl; // get variable
    p.set("a", node(string("Hello"))); // set variable
    cout << p.get("a").v_string << endl; // get variable
}

=>

3
1
Hello

Project Euler 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

(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

(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 (Some of them are for Parenj.)

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 (Paren running natively)
  • Parenj (Paren running on the Java Virtual Machine)
  • 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

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.