Appendices · reference

What scripts cannot use

4 min read · 2026-09-02 · config-weave 0.1.0

Two lists follow. The first names the wscript standard library modules that config-weave does not register, so a use line for one of them fails to compile. The second names the language features wscript leaves out by design, so a script cannot reach for them at all. Every host module config-weave does register is listed in The host API.

Standard library modules that are not registered

rust

use math      // error: unknown module
use process   // error: unknown module

The wscript standard library ships math, process and fs modules. config-weave registers none of these three. A use line naming one is a compile error at config-weave validate time, and a bare fs in a script means the config-weave module, not the standard library one. The standard library's value, json, toml, xml, regex and time modules are registered as they are.

Module	Why it is absent	Use instead
math	Scripts converge configuration; the arithmetic they need is + - * / % and comparisons.	Plain operators. int() truncates and float() widens.
process	Direct process spawning would bypass config-weave's output capture and logging.	shell module for run, bash and powershell; env module for environment variables.
fs (standard library)	config-weave's own fs adds metadata, glob, temp files and directories, and symlinks.	fs module, which is what use fs resolves to.

The config-weave fs module wins the name because a registered host module always takes precedence over anything else called fs. There is nothing to migrate: a script written for the standard library fs keeps its use fs line and gains the extra functions. Structured data has its own homes. JSON and TOML are the standard library modules, documented as json module and toml module. XML is the standard library module, documented as xml module. INI is not in the standard library and lives in the config-weave data module.

Language features wscript leaves out

rust

let r = &x                 // error: no references
if 1 { }                   // error: condition must be bool
let n = 1 + 2.0            // error: no implicit conversion
let mask = flags & 0x04    // error: no bitwise operators

These absences are deliberate. Each row names the feature and what a script writes instead.

Absent	Instead
Borrow checker, & and &mut, lifetimes	Reference counting. Reference types alias on assignment and self is by reference. See reference semantics.
Generic structs, enums and traits	Generic functions with the bounds Eq, Ord and Clone, plus the built-in List[T] and Map[K, V].
Exceptions	Result and ?. A fault is delivered to config-weave and ends the step; see faults.
Async, threads sharing values	Each step runs in its own VM. Parallelism is the scheduler's job; see Scheduling and concurrency.
Implicit conversions, truthiness	int(x) and float(x); a bool condition.
A cycle collector	A reference cycle leaks until the step ends. Use weak[T] for back-references.
Bitwise operators	Write the arithmetic out with *, / and %.
Dimensional analysis across unit families	A units family checks within itself. Declare one family per dimension.
Format specs inside interpolation holes	"{expr}" only. Use fmt("{:.2}", x) for formatting; see the prelude.
Range values outside a for header	Write 0..n in a for header only.
Bindings inside an or-pattern	Split the arms, or bind in a single pattern and test with a guard.
Default method bodies and trait inheritance	Implement every trait method on every type.

Some restrictions from wscript's first release have since lifted, and a script may use them freely: use of another script file from lib/, {expr} interpolation in every string literal, compound assignment such as +=, associated functions called as Type::func(...), generic functions, and unit families on numeric types.