An one-line Brainfuck interpreter in D.

tinyBrainfuck.d

import std.algorithm,
       std.string,
       std.array,
       std.stdio,
       std.conv;
import core.memory;

/*
  Useing raw pointer and manually memory manegement for perfourmance.
  D's dynamic array is very useful but a litle slower but safe.
  On the other hand handling raw pointer is not safe but more faster.
*/

// Z Combinator : Anonymous recursion
R delegate(Args) Z(R, Args...)(R delegate(R delegate(Args), Args) f) {
  return (Args args) => f(Z(f), args);
}

void main() {
  ((string input) =>
    (operators =>
      ((char* code) =>
        ((ubyte* memory) =>
          ((ulong memoryIndex) =>
            (removeTrash =>
              (process =>
                process(input)
              )((string input) =>
                  ((string[] _code) =>
                    (
                      (
                        GC.realloc(code,   _code.length *  char.sizeof, GC.BlkAttr.NO_SCAN | GC.BlkAttr.APPENDABLE),
                        GC.realloc(memory, _code.length * ubyte.sizeof, GC.BlkAttr.NO_SCAN | GC.BlkAttr.APPENDABLE)
                      ),
                      Z((int delegate(int) copy, int i) => i < _code.length ? (code[i] = _code[i].to!char, copy(i + 1)) : 0)(0),
                      ((int pc) =>
                        (optimizer =>
                          ((int delegate() destructor) =>
                            ((int[int] brackets) =>
                              (process =>
                                (
                                  process(int.init),
                                  destructor()
                                )
                              )(Z((int delegate(int) process, int index) =>
                                  index < _code.length 
                                  ? ((char current) =>
                                      (
                                        (current == '>'
                                          ? memoryIndex++
                                       : current == '<'
                                          ? memoryIndex--
                                       : current == '+'
                                          ? memory[memoryIndex]++
                                       : current == '-'
                                          ? memory[memoryIndex]--
                                       : current == '.'
                                          ? (
                                              write(memory[memoryIndex].to!char),
                                              stdout.flush()
                                            )
                                       : current == ','
                                         ? ((string buf) =>
                                              (
                                                Z((int delegate() getLine) => ((buf = readln()) == null || !buf.length) ? getLine() : 0)(),
                                                memory[memoryIndex] = cast(ubyte)buf[0]
                                              )
                                           )(string.init)
                                       : current == '['
                                         ? (memory[memoryIndex] == 0 ? (index = brackets[index], 0) : 0)
                                       : current == ']'
                                         ? (memory[memoryIndex] != 0 ? (index = brackets[index], 0) : 0)
                                       : 0
                                        ),
                                        process(index + 1)
                                      )
                                    )(code[index])
                                  : 0
                                ))
                            )(optimizer(int.init, (int[]).init, (int[int]).init))
                          )(() => (GC.free(code), GC.free(memory), memoryIndex = 0, 0))
                        )(Z((int[int] delegate(size_t, int[], int[int]) optimizer, size_t i, int[] leftstack, int[int] brackets) => 
                            i < _code.length ? 
                              ((char c) =>
                                !canFind(operators, _code[i])
                                  ? optimizer(i + 1, leftstack, brackets)
                                  : (
                                      c == '['
                                        ? (optimizer(i + 1, leftstack ~ pc++, brackets)) 
                                        : (c == ']' && leftstack.length != 0)
                                            ? (left =>
                                                (leftstack.popBack(),
                                                  (right =>
                                                    (
                                                      (brackets[left] = right, brackets[right] = left),
                                                      pc++,
                                                      optimizer(i + 1, leftstack, brackets)
                                                    )
                                                  )(pc))
                                              )(leftstack[$ - 1])
                                            : (pc++, optimizer(i + 1, leftstack, brackets))
                                    )
                              )(code[i]) : brackets
                            )
                        )
                      )(int.init)
                    )
                )(removeTrash(input))
              )
            )((string key) => key.split("").filter!(x => operators.canFind(x)).array)
          )(ulong.init)
        )(cast(ubyte*)GC.malloc(300000 * ubyte.sizeof, GC.BlkAttr.NO_SCAN | GC.BlkAttr.APPENDABLE))
      )(cast(char*) GC.malloc(300000 *  char.sizeof, GC.BlkAttr.NO_SCAN | GC.BlkAttr.APPENDABLE))
    )([">", "<", "+", "-", ".", ",", "[", "]"])
  )(">+++++++++[<++++++++>-]<.>+++++++[<++++>-]<+.+++++++..+++.[-]>++++++++[<++++>-]<.>+++++++++++[<+++++>-]<.>++++++++[<+++>-]<.+++.------.--------.[-]>++++++++[<++++>-]<+.[-]++++++++++.");
// => Hello World!
}