How Frothy Is Different

Frothy is a small language that runs on the board. You send code to the board while it runs. A definition takes effect at once, and a call runs at once. When you define a word again, the next call uses the new word. You do not build firmware or upload it again, and the board does not restart.

The Board Keeps And Shows Your Program

save writes your words to the flash of the board. After a restart, the board loads them, and it runs a word named boot if you define one. The board does not need the computer that wrote the words.

The board can also show you what it has. words lists the names, and see prints the code of a word:

see led.toggle
base source code
to led.toggle [ gpio.toggle: $led_builtin ]

Choose Frothy When

• you want to try a board, a sensor or an idea one line at a time;
• you want the board to keep its program and to show it to you again;
• you teach, and you want each line to act on the hardware at once.

Choose Another Tool When

• you need floating-point numbers, SPI, UDP, MQTT or HTTPS;
• you need a ready-made library for a display or another complex part;
• your program is large: an ESP32 board holds 256 of your names, an RP2040 board holds 192, and Limits lists the other sizes;
• you need a prompt over Wi-Fi or Bluetooth, or a prompt with a password;
• your board is not one of the supported boards .

Coming from Arduino shows how the parts of a sketch map to Frothy.

Design Choices

• Stable names. A top-level name always refers to the same slot. When you define a word again, its callers use the new code at their next call.
• No captured locals. Code reads its own parameters and locals, and the top-level names. An event body cannot read the locals of the word that registered it.
• Fixed memory. Each table has a fixed size. When a table is full, the board stops the form with error 4 and names the table.
• The prompt owns save, restore and dangerous.wipe. A running word cannot call them, so a program cannot replace itself.
• Safe boot on ESP32 boards. For 600 ms after start, Ctrl-C or the BOOT button skips the saved program. On an RP2040 board, Ctrl-C stops a boot that does not end.
• The serial prompt comes first. Any serial terminal can use a Frothy board. The browser editor, the CLI and the VS Code extension use the same prompt.