3. REPL

The REPL reads an entry, evaluates each of its top-level forms on its own, and prints each result as one canonical DUST form. A list keeps its brackets, so [1 2 (+ 3 4)] prints [1 2 7]. It keeps history and highlights input as you type. A form that spans lines continues until its brackets balance. 

> (+ 1 2)
   compile 77.9µs · 143.1KiB arena · key 5d902e22 · 1/64 cached
3  eval 57.9µs cpu · 130.5KiB peak · +4.6KiB net · 323.5KiB live
> (+ 1 2)
3  eval 17.3µs cpu · 128.5KiB peak · +2.5KiB net · 326.0KiB live

A local form defines a top-level local that later entries read: 

> (local rate 3)
   compile 47.9µs · 129.0KiB arena · key 64c24dfd · 2/64 cached
.rate  eval 10.6µs cpu · 5.7KiB peak · +3.3KiB net · 580.8KiB live
> [.rate (* .rate 2)]
   compile 81.8µs · 130.3KiB arena · key eb0abee0 · 3/64 cached
[3 6]  eval 8.1µs cpu · 8.4KiB peak · +5.5KiB net · 586.3KiB live

Table of Contents

3.1. Loading namespaces ↑

!load PATH [ALIAS] evaluates a file and binds each local its export forms name under a namespace as a constant. The file's other locals stay private. PATH is relative to the working directory and the .dust extension is implied. The namespace is ALIAS, or else the last path segment. Loading a namespace again replaces its bindings. A namespace whose names match library entries, such as math/pi, is rejected with #err <conflict name>; load it under an alias instead, as in !load lib/math m. A line that starts with ! is a REPL command; every other line is DUST, so :shapes/square is a constant reference.

Given lib/shapes.dust: 

(local double (fn [x] (+ .x .x)))
(local square (fn [x] (* .x .x)))
(export square double)

> !load lib/shapes
shapes: square double
> (shapes/square 7)
49  eval 140.8µs cpu · 116.8KiB peak · -128.6KiB net · 209.7KiB live
> !load lib/shapes s
s: square double
> (s/double 4.5)
9.0  eval 17.7µs cpu · 130.5KiB peak · +5.8KiB net · 228.0KiB live

What a library path names is up to each runtime. The REPL reads files; Stardust resolves the same paths within its database.

!reset drops every top-level local, loaded namespace, and compiled entry and starts a fresh runtime with only the core libraries: 

> !load lib/shapes
shapes: square double
> !reset
reset: locals, namespaces, and compiled programs cleared
> (shapes/square 7)
#err {<expected function>
      message "expected a function value"}  eval 28.3µs cpu · 144.4KiB peak · -136.6KiB net · 539.7KiB live