Esolang Interpreters #2 - Custom Smallfuck Interpreter

About this Kata Series

"Esolang Interpreters" is a Kata Series that originally began as three separate, independent esolang interpreter Kata authored by @donaldsebleung which all shared a similar format and were all somewhat inter-related. Under the influence of a fellow Codewarrior, these three high-level inter-related Kata gradually evolved into what is known today as the "Esolang Interpreters" series.

This series is a high-level Kata Series designed to challenge the minds of bright and daring programmers by implementing interpreters for various esoteric programming languages/Esolangs, mainly Brainfuck derivatives but not limited to them, given a certain specification for a certain Esolang. Perhaps the only exception to this rule is the very first Kata in this Series which is intended as an introduction/taster to the world of esoteric programming languages and writing interpreters for them.

The Language

Smallfuck is an esoteric programming language/Esolang invented in 2002 which is a sized-down variant of the famous Brainfuck Esolang. Key differences include:

• Smallfuck operates only on bits as opposed to bytes
• It has a limited data storage which varies from implementation to implementation depending on the size of the tape
• It does not define input or output - the "input" is encoded in the initial state of the data storage (tape) and the "output" should be decoded in the final state of the data storage (tape)

Here are a list of commands in Smallfuck:

• > - Move pointer to the right (by 1 cell)
• < - Move pointer to the left (by 1 cell)
• * - Flip the bit at the current cell
• [ - Jump past matching ] if value at current cell is 0
• ] - Jump back to matching [ (if value at current cell is nonzero)

As opposed to Brainfuck where a program terminates only when all of the commands in the program have been considered (left to right), Smallfuck terminates when any of the two conditions mentioned below become true:

• All commands have been considered from left to right
• The pointer goes out-of-bounds (i.e. if it moves to the left of the first cell or to the right of the last cell of the tape)

Smallfuck is considered to be Turing-complete if and only if it had a tape of infinite length; however, since the length of the tape is always defined as finite (as the interpreter cannot return a tape of infinite length), its computational class is of bounded-storage machines with bounded input.

More information on this Esolang can be found here.

The Task

Implement a custom Smallfuck interpreter interpreter() (interpreter in Haskell and F#, Interpreter in C#, custom_small_fuck:interpreter/2 in Erlang) which accepts the following arguments:

1. code - Required. The Smallfuck program to be executed, passed in as a string. May contain non-command characters. Your interpreter should simply ignore any non-command characters.
2. tape - Required. The initial state of the data storage (tape), passed in as a string. For example, if the string "00101100" is passed in then it should translate to something of this form within your interpreter: [0, 0, 1, 0, 1, 1, 0, 0]. You may assume that all input strings for tape will be non-empty and will only contain "0"s and "1"s.

Your interpreter should return the final state of the data storage (tape) as a string in the same format that it was passed in. For example, if the tape in your interpreter ends up being [1, 1, 1, 1, 1] then return the string "11111".

NOTE: The pointer of the interpreter always starts from the first (leftmost) cell of the tape, same as in Brainfuck.

Good luck :D

Kata in this Series

1. Esolang Interpreters #1 - Introduction to Esolangs and My First Interpreter (MiniStringFuck)
2. Esolang Interpreters #2 - Custom Smallfuck Interpreter
3. Esolang Interpreters #3 - Custom Paintfuck Interpreter
4. Esolang Interpreters #4 - Boolfuck Interpreter