Decimo v0.13.0

20260822 (v0.13.0)

Decimo v0.13.0 is a traits release. Numeric, Parsable and Rootable let code be written once and run over BigInt, BigUInt, BigDecimal, Decimal128 and BigFloat alike — a matrix library asking for T: Numeric & Rootable is the motivating case. BigInt gains /. The errors module is reworked so that the error kinds are functions returning a plain Error, which is a breaking change for code that spells a typed raise such as raises ValueError in its own signatures.

⭐️ New in v0.13.0

Traits (decimo.traits):

1. Numeric — zero(), one(), -x, +, -, * and /, conformed to by BigInt, BigDecimal and Decimal128. Enough for the whole of dense linear algebra. Every operation is declared raises, the widest signature, so a non-raising implementation conforms unchanged (PR #265).
2. Parsable — the static from_string(), and the counterpart of Writable: it lets a container be filled from a literal without knowing which number type it holds. Same three types (PR #266).
3. Rootable — sqrt(), conformed to by five types, BigUInt and BigFloat included. It is separate from Numeric because those two can never be Numeric: BigUInt is unsigned and so has no __neg__, and BigFloat is Movable without being Copyable. What the root means stays the implementing type's business — on an integral type it truncates, so BigInt("10").sqrt() is 3, and a negative value raises on the four exact types but yields nan on BigFloat (PR #268).

Other additions:

1. BigInt.__truediv__ — / on integers is closed and truncates toward zero, matching Mojo's own Int: BInt(-7) / BInt(2) is -3 where BInt(-7) // BInt(2) is -4. The two operators differ exactly when the operands have opposite signs (PR #265).
2. BigDecimal.zero() / one() and Decimal128.zero() / one(), the Numeric spelling of the identities. Decimal128.ZERO() and ONE() stay as they are (PR #265).
3. PRECISION (28, the same default as Python's decimal) is exported from the top level, so a caller can name the default it is getting (PR #268).

🦋 Changed in v0.13.0

Errors (PR #267):

1. The error kinds are now functions, not aliases for a parametrised payload type: ValueError, OverflowError and the rest return a plain Error, so an enclosing function needs nothing beyond a bare raises. Raise sites are unchanged, but a signature can no longer be spelled raises ValueError — a typed raise is invariant in Mojo v1.0.0, which cuts such a function off from std.testing and from any ordinary helper. BaseError is now the payload only.
2. A new comptime toggle _USE_COLOUR blanks every ANSI escape, for when the tracebacks go to a log file rather than a terminal. Chained tracebacks gain a blank line after the separator, and a frame now names the function it was raised in.

Signatures (PR #268):

1. BigDecimal.sqrt() splits its defaulted precision into the overloads sqrt(self) and sqrt(self, precision), since in Mojo a default argument does not satisfy a trait signature. Existing calls are unaffected.
2. root() converges on one spelling, root(self, n: Int), which BigDecimal, Decimal128 and BigFloat now all accept. BigDecimal keeps its BigDecimal-degree overloads for non-integral roots and BigFloat its UInt32 one. Every existing call keeps working. root is deliberately not part of Rootable: BigInt and BigUInt have no nth root to offer.

Documentation and tooling:

1. Markdown across the repository is reformatted — long lines rewrapped and list formatting made uniform — and argmojo is an active Pixi dependency again, pinned to >=0.8.0,<0.9.0 now that modular-community ships it (PR #264).
2. The user manual's Appendix B documents the three traits and which types conform; the BigInt division section covers the new / (PR #265, #266, #268).
3. The test suite numeric is renamed to traits, with numeric and num kept as aliases and the tests moved to tests/traits/ (PR #266, #267).
4. tests/test.sh bug fix: the retry loop read $? after an if, which is the if statement's own status — zero — so a suite that failed to compile was reported as passing. It now uses && (PR #268).