The language can be compiled to brainfuck in a 1:1 relationship if the A command is not used.
4RL, like brainfuck, operates on a tape, each cell in the tape is initialized to zero. The tape is 2^16 bytes long, each cell being one byte.
The commands are equivalent to brainfuck:
|4||+||Increment tape cell at pointer|
|r||-||Decrement cell pointer|
|e||>||Advance pointer to next cell|
|a||<||Retreat pointer to previous cell|
|l||[||If value under pointer is zero, jump to matching L|
|R||,||Take user input, store it in the cell under pointer|
|E||.||Output value under pointer as ASCII character|
|L||]||If value at pointer is not zero, jump to matching l|
Here is a hello world program