Module

Evaluates an expression with local variables, fresh on every call.

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Module({x, y = y0, ...}, body)

body

, evaluated with

x

y

, ... as fresh local variables (each initialized, or left unbound, per its own binding) invisible outside the call.

Typed signatures

Type	Package	Applies
`(any, any) -> any`	`combinatorics`	always

Domain: Collections

Details

Each call gets its own scope, so a recursive or repeated $Module$ call never has its locals collide with an outer binding — or another call's — of the same name.
An initializer's value (the $y0$ in $y = y0$ ) is computed in the OUTER context, before any local shadows it, same as With — a later binding cannot read an earlier one's local value.
A binding with no = value (a bare $x$ ) declares an uninitialized local; referencing it before assigning gives an unevaluated symbol, not an error.

Examples

Basic #

a local counter, invisible outside

\mathrm{Module}(\bigl\lbrack k=0\bigr\rbrack, k\coloneq k+1)

Out

1

Scope #

two calls' locals of the same name don't collide

\bigl\lbrack\mathrm{Module}(\bigl\lbrack n=10\bigr\rbrack, n+1), \mathrm{Module}(\bigl\lbrack n=20\bigr\rbrack, n+1)\bigr\rbrack

Out

\bigl\lbrack11, 21\bigr\rbrack

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