01. What Frothy Is

Frothy is easiest to learn if you start with three laws from the accepted language spec:

  1. The top level is a board of stable named slots.
  2. Code only does a small number of things: read, bind, set, call, choose, and repeat.
  3. Persistence remembers the overlay image, not the current execution.

That is the center of the language. Frothy is not organized around a user-visible stack. It is organized around values, places, and a live image you can inspect and recover.

A Tiny Example

unit is 75

to pulse with pin [
  gpio.high: pin;
  ms: unit;
  gpio.low: pin
]

to blink with pin [
  repeat 3 [
    pulse: pin;
    ms: unit
  ]
]

blink: LED_BUILTIN

Read that as ordinary named code:

  • unit is a top-level slot
  • pulse and blink are top-level Code values
  • repeat is a loop expression
  • gpio.high and ms are base-image board bindings

If you redefine blink, old callers see the new definition because they still resolve through the same stable top-level slot.

What Changed From Froth

Frothy keeps the best substrate ideas from Froth:

  • live interaction on the device
  • coherent redefinition
  • persistence and recovery
  • transparent inspection

But it deliberately drops the old stack-centric public model. In Frothy, values are read by name, locals are lexical, and code is just another value.

The First Things To Keep In Your Head

  • name is expr creates or rebinds a stable top-level slot.
  • to name [...] is just sugar for binding a Code value.
  • fn [...] creates anonymous Code.
  • save, restore, and dangerous.wipe operate on the overlay image.
  • The device is the real environment. Host tools help you get there faster.

Next: Values, names, and rebinding .