REPL

rad repl starts an interactive session. You type Rad, it runs it, and whatever you define stays defined until you leave.

$ rad repl
🤙 Rad REPL v0.12.0
Type ':help' for help, ':exit' or Ctrl+D to quit.

> name = "world"
> upper(name)
"WORLD"

An expression prints its value; an assignment prints nothing. Values print the way you would write them, so a string comes back quoted and you can tell "5" from 5. print() is still there when you want the unquoted form.

Blocks take several lines

A block construct keeps taking lines until you enter a blank one. Rad scopes blocks by indentation, so there is no closing token to look for - the blank line is what says you are done. The prompt changes to . while the REPL is still gathering, and the next line is indented for you.

> fn greet(name):
.     print("hi {name}")
.
> greet("world")
hi world

Everything with a body works this way: if, for, while, switch, named fn, and catch: blocks. A blank line also gets you out of a buffer you would rather abandon - though Ctrl+C is quicker, and throws the whole thing away.

Pasting a multi-line block works too. The REPL can tell a pasted newline from a pressed Enter, so the whole snippet arrives before anything runs.

Mistakes don't end the session

An error prints the same diagnostic it would print in a script, and then you get your prompt back:

> x = 5
> undefined_variable
error[RAD20028]: Undefined variable: undefined_variable
  --> <repl>:1:1
  |
1 | undefined_variable
  | ^^^^^^^^^^^^^^^^^^
  |
  = info: rad docs RAD20028

> x
5

Ctrl+C interrupts whatever is running - a slow shell command, an HTTP request, a loop that turned out to be infinite - and returns you to the prompt with the session intact. Press it twice if something is truly wedged; the second one exits immediately.

Editing

The line you are typing is editable:

Key	Does
← →	move the cursor
Ctrl+A / Ctrl+E	jump to start / end of line
Ctrl+W	delete the word behind the cursor
Ctrl+K	delete to end of line
Ctrl+U	delete the line
↑ ↓	recall earlier input
Ctrl+C	abandon this line
Ctrl+D	leave (on an empty line)

Inside a multi-line block, ↑ and ↓ move between the lines you are typing and only reach for history once the cursor is already at the top or bottom.

History lasts for the session and is not written to disk.

Commands

A line starting with : is a REPL command rather than Rad:

Command	Does
:help	the summary
:vars	variables you have defined
:docs <topic>	docs for a function, an error code, or a guide page
:load <file>	run a .rad file into this session
:clear	clear the screen
:reset	forget every variable and start over
:exit, :quit	leave

:docs takes anything rad docs takes:

> :docs upper
> :docs RAD20028
> :docs guide/shell-commands

:load runs a file's statements against your session, so the functions and variables it defines are yours afterwards. It is the way to work on a script and try its pieces without pasting them.

Two things behave differently than in a script

defer runs at the end of the turn that registered it, not when the session ends. A turn is the REPL's whole notion of a script. Holding a defer until you quit would mean it does nothing observable for as long as you keep working, and never runs at all if a later turn ends badly.

args blocks, command blocks, and file headers are refused. All three describe how a script is invoked from a command line, and a session was not invoked from one. Put the script in a file and :load it, or run it normally to exercise its argument parsing. See RAD20049 for the details.

Piping input

With no terminal to draw on - a pipe, CI, an agent's tool call - rad repl reads lines and prints results without drawing a prompt:

$ printf 'x = 20\nx * 2\n' | rad repl
🤙 Rad REPL v0.12.0
Type ':help' for help, ':exit' or Ctrl+D to quit.

40

Blocks work the same way, blank line and all. This is also how the REPL's own tests drive it.

What it doesn't do yet

No tab completion, no syntax highlighting, no Ctrl+R search, and no history file that survives the session. None of these are ruled out; they just aren't built.