Good practice

How Nerve is meant to be written: the practices its rules make easy. They’re advice, not rules — the compiler enforces none of them.

Names are free

A quoted name may be anything, and no style for it is recommended.

Types and values

1Let Precog choose inside the program; write types at the doors

:= everywhere inside; an explicit type where the outside world comes in — input, extern, struct fields, public functions. That is the third pillar used as meant.

2Narrow an outside value once, where it arrives, with a range type

'text' := std::input.line[] otherwise "";
'n' := to.int32[1, 99]['text'] otherwise 1;

Everything downstream is then proven, with no guard at each use.

3No mut by habit

Plain is the standard, and change already marks every change. Keep !mut / !$ for values whose fixedness matters to the reader: a rate, a limit.

Safety

4The proven path first, then check

A guard if in front of the site, and check on the ones that matter, so the compiler says whether the guard is enough. !check is for what no guard can prove, mostly C.

5Wrap !check once

As std does: one small function holds the !check C call, and everything else calls that safe wrapper. The build's !check list stays short enough to review.

6NO_FUCKING_CHECKS only after measuring

Never a first resort.

7#strict for public Limbs, plain files for programs

A library's safety should not depend on who calls it, and #strict makes sure it does not.

Ownership and failures

8lend by default, give when the receiver should own it, copy rarely

Every copy is a visible allocation; many of them mean the design is off.

9Handle a failure where its cause is understood

otherwise with one arm per reason close to the source, otherwise fail to pass it up. Careful with otherwise 0 on input: it can turn "bad input" into a zero that looks real.

10and.then for guards

if 'i' </== list.length[lend 'xs'] and.then 'xs'['i'] == 5 { … }. A plain and runs both sides.

Loops and output

11A plain for; Precog parallelises

seq only when order matters, para only after measuring, simd only when the plain loop did not vectorise, !cheat only for timing code.

12print.useful for people, print for debugging numbers, print.format for shaped output

(columns, hex, places).

13precedence.low_first for a Limb's operator levels

(owner, 2026-10-03: "low_first is good practice"): level 1 binds loosest, as a precedence table is read top to bottom. precedence.high_first is there for whoever thinks the other way.