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A file shares only what it marks `pub`, so its helpers stay its own business

Each file is a module, named by its path: src/pricing.hd is pricing. A declaration is private to its file unless it says pub, and another file sees a public name only after it asks for it with use. So the shipping fee rule in fee can change, or vanish, without breaking any other file: no other file can call it. The use line at the top of a file lists everything it takes from elsewhere, and the pub items of a file are its whole interface. Open the pricing.hd tab to see both sides.

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use pkg.pricing.{Line, total} # ← the names this file takes from pricing.hdpub fn main() -> void $ Console: cart := [Line { item: "lamp", cents: 3200 }, Line { item: "bulb", cents: 450 }] println("total: ${total(cart)} cents")# `fee` in pricing.hd has no `pub`. Ask for it anyway: change the# first line to `use pkg.pricing.{Line, total, fee}` and Run:# private-import: 'fee' is private to module 'playground.pricing'

# Public: the interface other files may use.pub struct Line: pub item: string pub cents: i32pub fn total(lines: List[Line]) -> i32: subtotal := lines.iter().fold(0, fn(sum: i32, line: Line) -> i32: sum + line.cents) subtotal + fee(subtotal)# Private: only this file can call it, so this rule can change freely.fn fee(subtotal: i32) -> i32: if subtotal >= 5000: 0 else: 499

A file shares only what it marks pub, so its helpers stay its own business

A file shares only what it marks `pub`, so its helpers stay its own business