elixir_brainfuck_part_one.exs

defmodule Brainfuck do

	# opcodes
	@op_vinc "+" # increment value at memory address
	@op_vdec "-" # decrement value at memory address
	@op_pinc ">" # increment memory address
	@op_pdec "<" # decrement memory address
	@op_putc "." # output byte at memory address
	@op_getc "," # input byte into memory address
	@op_lbeg "[" # loop begin
	@op_lend "]" # loop end

	@empty ""

	def run(program), do: run(program, 0, [0], @empty)

	# final condition
	defp run(@empty, addr, mem, output), do: {addr, mem, output}

	# commands
	defp run(@op_vinc <> rest, addr, mem, output) do
		run(rest, addr, mem |> inc_at(addr), output)
	end
	defp run(@op_vdec <> rest, addr, mem, output) do
		run(rest, addr,  mem |> dec_at(addr), output)
	end

	defp run(@op_pinc <> rest, addr, mem, output) do
		run(rest, addr+1, mem, output)
	end

	defp run(@op_pdec <> rest, addr, mem, output) do
		run(rest, addr-1, mem, output)
	end

	defp run(@op_putc <> rest, addr, mem, output) do
		run(rest, addr, mem, output <> (mem |> char_at addr))
	end
	
	defp run(@op_getc <> rest, addr, mem, output) do
		val = case IO.getn("Input\n", 1) do
			:eof -> 0
			c    -> c
		end
		run(rest, addr, mem |> put_at(addr, val), output)
	end

	# drop every other character
	defp run(<<_>> <> rest, addr, mem, output), do: run(rest, addr, mem, output)


	# helpers
	defp inc_at(list, addr), do: List.update_at(list, addr, &(&1+1 |> rem 255))
	defp dec_at(list, addr), do: List.update_at(list, addr, &(&1-1 |> rem 255))
	defp put_at(list, addr, val), do: List.replace_at(list, addr, val)

	defp byte_at(list, addr), do: list |> Enum.at addr
	defp char_at(list, addr), do: [list |> byte_at addr] |> to_string

end

@wstucco you might consider adding elixir benchmarks to: https://github.com/kostya/benchmarks