Calculator

programs/calc.fj — an interactive REPL that parses two numbers and one operator from stdin, evaluates, and prints the result. Supports +, -, *, /, %, decimal or hexadecimal input.

> 12345 + 67890
80235
> 0xff * 0xff
0xfe01

The full program is ~600 lines — too long to inline. The shape:

stl.startup

loop:
    bit.zero hex_used
    bit.print 3, prompt_string
    getch
    remove_spaces
    check_quit should_quit, before_start
  // ... lots of parsing helpers ...

    insert_number a
    bit.mov 8, op, ascii
    insert_number b
    calc a, op, b
    bit.print_dec_int 64, result
    ;loop                  // back to the top

View on GitHub.

What it demonstrates

• Stateful input parsing. A getch helper, character-by-character whitespace skipping, hex/decimal mode detection.

• Conditional dispatch. bit.cmp chains for +/-/*///% opcode routing.

• Error handling. A dedicated err_loop label that prints an error message and restarts the prompt without aborting.

• Multi-pass output. The result is printed in decimal or hex depending on whether either operand was hex-input.

Why it’s useful to read

The calculator is the smallest non-trivial program in the upstream repo that exercises macros from every STL submodule. Reading it end to end is the fastest way to internalise how bit.*, hex.*, stl.fcall/stl.fret, and the I/O wrappers compose into a real program.