Appendices

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A. Sigil & operator cheat-sheet

Sigils & literal markers

Operators

Operator precedence

Loosest → tightest, all left-associative: || · && · == != · < <= > >= · ~ · .. · + - · * / % · <--. Postfix sends (.method) bind tighter than any infix operator; prefix operators (- ! %) bind tightest.

B. Selector / desugaring quick-reference

C. Gotchas for writing & generating Quoin

The consolidated list of surprising behaviors. If you're producing Quoin code, read this first.

1. Operator precedence is conventional (* / % tighter than + - tighter than comparison tighter than &&/||), with two specifics: range .. is looser than arithmetic (2 .. n + 1 = 2 .. (n + 1)), and postfix .method binds tighter than any infix operator (1 .. list.count = 1 .. (list.count)).
2. " always starts a comment — there are no double-quoted strings. A "…" block comment spans newlines, so a stray " silently swallows code until the next quote. Strings are '…'.
3. Conditionals are strict; combinators coerce. if:/else:/whileDo: require a real Boolean — nil.if:{…}, 42.if:{…}, and {5}.whileDo:{…} all raise (MessageNotUnderstood). But &&/|| short-circuit on truthiness and return the operand value, and ! maps any value to a Boolean. Use ==, <, defined?, etc. to build conditions.
4. Assignment is a statement, not an expression. b = (a = 5) is a parse error; you can't assign inside a condition or argument.
5. Ranges are half-open. 1..5 yields 1 2 3 4; the end is excluded (both directions: 5..1 → 5 4 3 2).
6. ^ returns from the block, ^^ from the method. Inside an iterator block (each:, collect:), ^ only ends that iteration — use ^^ to break out of the surrounding method.
7. Block arity is unchecked. Too few arguments → missing params are nil; too many → extras are ignored. No error either way.
8. Redefining overrides; type/guard variants coexist. A later same-signature definition (same param types, no guard) replaces the earlier — bar -> {1} then bar --> {2} makes bar return 2. Variants that differ by parameter type or carry a guard are kept as distinct multimethods, dispatched by argument by specificity (a guarded variant outranks an equal-typed unguarded one). Definition order is not a tiebreaker: two equally-specific variants that both match raise AmbiguousMethodError — pair specific guards with one unguarded catch-all (|x|), or use case/~ for ordered matching.
9. new:{} doesn't capture lexical scope, and super doesn't exist. An empty new:{} leaves fields nil; only explicit assignment binds a field (its RHS is lexical, but it never mutates the outer variable). A plain-assignment init: { |a| @a = a } is redundant. A child sets a parent's field via @field.
10. .sealed! / .abstract! are enforced. .sealed! freezes a class (or instance eigenclass) — no <--/->/-->/.mix:/subclassing — and .abstract! forbids instantiating the class itself (subclasses still instantiate). Call .sealed! last in a body, since defs after it are rejected.
11. case: matches with ~, not ==. Ranges, regexes, classes, and predicate blocks all match; the first matching when: wins. Order clauses most-specific-first.
12. throw takes any value, but catch-by-type needs Errors. To dispatch with TypeError ~ e (the matcher class is on the left of ~), throw Error subclasses (or use Error.throw:).
13. % has three meanings. Infix between numbers = modulo; infix on a string = printf-style %:; prefix on a string = %{…} interpolation (mod).
14. <- vs =. <- defines a once-only constant/class (redefining throws); = is a reassignable local. They're not interchangeable.
15. Fibers throw on misuse. Resuming a done/failed fiber, yielding outside a fiber, or self-resuming all raise FiberError. Guard with alive?/done?.
16. A leading . or operator continues the previous line. A newline ends a statement only when unambiguous; a line starting with . (a message send) or an infix operator attaches to the line above. method -> {} ⏎ .mix:Mixin parses as (method -> {}).mix:Mixin. End the previous line with ; when the next starts with . or an operator — which is why stdlib code uses ; heavily.
17. use loads files; it doesn't import names. use path; runs a .qn file once (a repeat/cyclic use is a no-op), and its definitions land as ordinary [Ns] globals — there's no local import scope, and aliasing is just X = [Ns]Name. use is a soft keyword (still usable as an identifier). Packages: bare/std: = stdlib, self: = your project; dir/* globs a directory (sorted). See §47.
18. Inside a collection literal, spacing decides whether + - % is a prefix or an infix operator. Elements are juxtaposed expressions (so #(a + b c) is two elements), which makes #(-1 -2) ambiguous. The rule, in #( … ), #Name( … ) and #< … >: an operator detached from its left operand and glued to its right one is a prefix and starts a new element. Every other spacing is infix.

So #(-1 -2) is two negatives, #(5-3) is #(2), and #('a' %'b%{x}') is a string plus an interpolation. Identifiers follow the same rule (#(a -b) is two elements), and the prefix binds tighter than the infix after it, so #(1 -2 + 3) is #(1 1). ! needs no rule: its infix form is the two-character !=. Parenthesize when in doubt: #((7-3)).

D. Glossary

• Selector — a method name, including its colons: at:put: is one selector with two argument slots. Operators are selectors too (+:, ~:).
• Multimethod — several definitions of one selector distinguished by argument type or guard; dispatch picks the most specific match (an equally-specific tie that both match → AmbiguousMethodError).
• Eigenclass / singleton — a per-object class created by value <-- { … }, holding methods for just that one object (named $Type internally).
• Mixin — a class included into another with .mix:; its methods and instance vars participate in lookup (before the parent).
• Block — a first-class closure { … }; the unit of deferred code used for control flow, iteration, and initialization.
• Block-local — a variable declared after - in a block header ({ |args - locals| }), initialized to nil.
• Fiber — a stackful coroutine; Generator and the external Iterator are built on fibers.
• Half-open range — a range that includes its start but excludes its end.
• Namespaced name — a global addressed as [NS]Name; bare names and [/]Name live in the root namespace.
• Unit / package — a .qn file loaded by use pkg:path (once, via the host's resolver). std:/bare = the stdlib, self: = the project. The load path is decoupled from the [Ns] namespace a unit registers under. (§47)

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