std/contract

Check a module against a module contract.

checkContract compares a contract declaration with a module's moduleInterface and returns Issues:

import { checkContract } from "std/contract"

gen fn pages(dir: String) -> String {
    let iface = moduleInterface(pageFile)
    let issues = checkContract(iface, contractOf(Page))
    ...
}

The compiler knows only the declaration form, so a third-party generator can declare its own contract. Every condition is reported:

• required member absent -> contract.missing
• member type mismatch -> contract.type
• unknown export, close to a member -> contract.unknown.didYouMean
• unknown export, not close -> contract.unknown
• open-rule shape mismatch -> contract.open

A module exports only functions (every top-level let is private), so a let member is satisfied by an accessor (export fn head() -> Head). A member with a default (fn head() -> Head = noHead()) is optional. A fn member name declared more than once has alternative signatures; the module matches any one, the name is optional when any alternative has a default, and matchedMember says which one matched:

fn head() -> Head = noHead()
fn head(d: T) -> Head
fn head(p: P) -> Head
fn head(p: P, d: T) -> Head