Prototypes, Modules, and Determinism

Back at the gate-side trunk, with the lane open before you and both stalls finally in sight, you set the last pages beside Juniper's bell.

Moonrise is close enough to silver the wagon rims. Mira works the bakery counter nearest the gate. Farther down the lane, Tavi polishes a kettle lid with his sleeve as if brightness might fix fate. Juniper pretends not to watch the queue and fails. You have not seen a market cut it this close since the Glass Coast rains. One last assembly, then the gates open.

# A prototype with a shared mood and description function.
<$stall-proto = (::
  mood = cozy;
  describe = [?: stall] {
    `<stall/name> hums with `<stall/mood> light.
  };
)>
<$stall = (:: name = "Moon Bakery")>
[set-proto: <stall>; <stall-proto>]
[stall/describe: <stall>]

Moon Bakery hums with cozy light.

The function stored on the prototype is just a normal function found through map lookup. Ranty does not pass a hidden self, so you hand the map in explicitly as stall. That keeps the magic small and readable when you are this close to opening.

Writes stay local, even when reads inherit

At first glance, it looks as if changing one stall might overwrite the shared defaults for every other stall.

Wrong expectation

<$defaults = (:: mood = calm)>
<$stall = (::)>
[set-proto: <stall>; <defaults>]
<stall/mood = excited>
<defaults/mood>

What happened

calm

The prototype kept its original value. Writes stay on the receiving map.

<$defaults = (:: mood = calm)>
<$stall = (::)>
[set-proto: <stall>; <defaults>]
<stall/mood = excited>
[proto: <stall>]\n
<stall/mood>\n
<defaults/mood>

(:: mood = calm)
excited
calm

Modules

The next example loads a tracked tutorial fixture from tests/sources/tutorial/. The fixture itself loads a sibling module through a relative path, so this doubles as a tiny module-system tour. This is the opening line you will hand back to Juniper when the gates swing wide.

@require kit: "tests/sources/tutorial/moon-market-kit"
[kit/opening-line: Juniper]

violet awnings rustle over Juniper's stall.
Specialty: ink-jam
Omen: the tea hums blue

Determinism with forks

[fork] lets you branch the random stream, and [unfork] returns to the previous one.

@require kit: "tests/sources/tutorial/moon-market-kit"
[fork: 99][kit/omen]\n
[unfork]
[kit/omen]

a moth lands on the till
three bells ring at once

That is the useful kind of determinism: the main stream stays predictable, but a nested sub-generator can have its own private randomness. Tavi gets his eerie side channel, and Juniper still gets reproducible tests.

Opening night, all together

The Moon-Market generator you have been assembling is still small, but it already has the same moving parts as many bigger interactive-fiction tools: reusable text, stored world state, branching tables, helper functions, formatting control, and modular pieces you can shuffle into new shapes.

If you want to run the final example from the CLI, the docs verifier uses the same basic idea:

ranty --seed 1 --eval '@require kit: "tests/sources/tutorial/moon-market-kit" [kit/opening-line: Juniper]'

violet awnings rustle over Juniper's stall.
Specialty: ink-jam
Omen: the tea hums blue

More information about prototypes, modules, and deterministic helpers can be found in the Ranty documentation for Map Prototypes, Prototype Patterns, @require, Modules, and General.

Juniper rings the bell at the gate and finally lets her shoulders drop. Mira slides the first tray of buns onto the counter nearest you and flashes a flour-bright grin. Farther down the lane, Tavi lifts the tea kettle, hears it sing properly at last, and laughs out loud. The awnings stir, the lanterns catch, and the Wandering Moon-Market opens on time. Juniper gives you one grave nod of thanks. When the first rush thins, Mira presses a warm star bun into your hand, and Tavi promises your omen will always get the best kettle.

Mission accomplished.

Coverage ledger

Feature family	First tutorial page
Text, comments, escape sequences, hinting, string literals	Text, Comments, Escapes, and Hinting
Accessors, setters, constants, `nothing`, fallback syntax, lazy definitions	Accessors, Variables, Constants, and Nothing
Lists, tuples, maps, access paths, slices, dynamic keys, anonymous accessors	Lists, Tuples, Maps, and Access Paths
Arithmetic, logic, comparison, truthiness, booleans, conditional expressions, compound assignment	Arithmetic, Logic, and Conditionals
Square-bracket calls, built-in helpers, ranges, user functions, lambdas, optional/default/lazy/variadic parameters, closures, `@return`, globals, descoping	Function Calls, Functions, and Ranges
Blocks, sinking, selectors, repetition, separators, `@weight`, `@on`, `match`, selector handles	Blocks, Selectors, and Sinking
`@step`, `@total`, `[step]`, control-flow charms, protected blocks, attribute keywords and mutators	Repetition State, Control Flow, and Attributes
Piping, pipeval, assignment pipe, parametric spread, temporal spread, synchronized spread, complex spread	Pipes and Argument Spreading
`@edit`, `@text`, whitespace formatting, number formatting, string polish helpers	Output Editing and Formatting
Prototypes, modules, `@require`, determinism with `fork` and `unfork`	Prototypes, Modules, and Determinism

From here, the best next step is not to reread the tutorial. It is to steal one page of it and turn that page into your own scene generator.

Previous: Output Editing and Formatting

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