The REPL

Start a session

Shell

ilo repl

You get an interactive prompt where you can define functions and evaluate expressions:

ilo

ilo> dbl x:n>n;*x 2
ilo> dbl 5
10
ilo> inc x:n>n;+x 1
ilo> inc 10
11

Functions, types, and aliases persist across lines. Build up a program incrementally.

Multi-line input

The REPL supports multi-line input for type definitions and functions. Continuation is triggered by:

• Unclosed braces - type definitions spanning multiple lines
• Trailing ; - signals more statements to come

> type point{
..   x:n
..   y:n
.. }
defined type: point{x:n;y:n}

> cls sp:n>t;
..   >=sp 1000 "gold";
..   >=sp 500 "silver";
..   "bronze"

defined: cls(sp:n) -> t

A blank line or balanced braces submit the input.

Pipes in the REPL

Chain functions you’ve already defined:

ilo

ilo> dbl x:n>n;*x 2
ilo> inc x:n>n;+x 1
ilo> 5 >> dbl >> inc
11

Commands

Command	What it does
:defs	Show all definitions (functions, types, aliases)
:w file.ilo	Save definitions to a file
:clear	Start fresh
:help	Show help
:q	Quit

JSON mode

For agent integration, use -j to get structured JSON output:

Shell

ilo repl -j

Success:

JSON

{"ok": 10}

Error:

JSON

{"code": "ILO-T004", "message": "undefined variable 'y'", "severity": "error", "suggestion": "did you mean 'x'?"}

The -j flag also works outside the REPL: ilo 'dbl x:n>n;*x 2' -j 5

Tips

• Define helper functions first, then compose them
• Use :defs to remind yourself what’s in scope
• Use :w to save a working session to a file when you’re happy with it