rtcl - A Lightweight Tcl-Compatible Scripting Language

A minimal, cross-platform Tcl interpreter implemented in Rust.

Features

• Lightweight: Designed for embedded systems and resource-constrained environments
• Cross-Platform: Runs on native, wasm32-unknown-unknown, and wasm32-wasip1 targets
• Tcl Compatible: Supports familiar Tcl syntax and commands
• Expect Support: Process automation capabilities similar to classic expect
• Embedded Ready: Optional embedded feature for no_std environments with alloc

Quick Start

Build

cargo build --release

Run a Script

# Execute a script file
./target/release/rtcl -f script.tcl
# Evaluate a command
./target/release/rtcl -c "puts hello"# Interactive REPL
./target/release/rtcl -i

REPL Commands

rtcl> set x 42
42
rtcl> puts "x = $x"
x = 42
rtcl> expr 1 + 2 * 3
7
rtcl> .exit

Supported Commands

Core Commands

Command	Description
set	Get or set a variable
puts	Print a string
if	Conditional execution
while	While loop
for	For loop
foreach	Iterate over list
expr	Evaluate expression
proc	Define procedure (limited)
return	Return from procedure
break	Exit loop
continue	Continue to next iteration

List Commands

Command	Description
list	Create a list
llength	Get list length
lindex	Get list element
lappend	Append to list variable
concat	Concatenate strings

String Commands

Command	Description
string length	String length
string range	Substring
string tolower	Lowercase
string toupper	Uppercase
string trim	Trim whitespace

Other Commands

Command	Description
incr	Increment variable
append	Append to string variable
catch	Catch errors
error	Throw error
info exists	Check variable
info commands	List commands
rename	Rename/delete command
eval	Evaluate script
uplevel	Evaluate in caller scope

Expression Syntax

Supports standard Tcl expressions:

expr 1 + 2 * 3 ; => 7
expr $x > 0 ; => 1 (true)
expr {$a == $b} ; comparison
expr {abs(-5)} ; function call

Supported operators: +, -, *, /, %, <, >, <=, >=, ==, !=, &&, ||, !

Supported functions: abs, int, double, round, floor, ceil, sqrt, pow, sin, cos, tan, log, exp, min, max

Expect Module

use rtcl_expect::{spawn,ExpectError};letmut proc = spawn("ssh",&["user@host"])?;
proc.expect("password:",Duration::from_secs(10))?;
proc.send_line("mypassword")?;

Project Structure

rtcl/
├── crates/
│ ├── rtcl-core/ # Core interpreter (cross-platform, wasm/wasi compatible)
│ ├── rtcl-cli/ # Command-line interface
│ └── rtcl-expect/ # Expect-style process automation
└── tasks/ # Task files for development

Platform Support

Target	Status
Native (Linux, macOS, Windows)	✅ Supported
wasm32-unknown-unknown	✅ Supported
wasm32-wasip1	✅ Supported

Usage on WebAssembly

# Cargo.toml
[dependencies]
rtcl-core = { version = "0.1", default-features = false }

use rtcl_core::{Interp,Value};letmut interp = Interp::new();
interp.eval("set x 42").unwrap();

Embedded / No-std Usage

For no_std environments with alloc:

# Cargo.toml
[dependencies]
rtcl-core = { version = "0.1", default-features = false, features = ["embedded"] }

#![no_std]externcrate alloc;use rtcl_core::{Interp,Value};letmut interp = Interp::new();
interp.eval("set x 42").unwrap();

Differences from Standard Tcl

1. Procedure definitions are simplified
2. No namespace support yet
3. Limited error stack traces
4. Some string commands may differ slightly

License

BSD 2-Clause License (same as jimtcl)