It's duct tape for your unix pipes. A programming language for doing small stuff fast and easy.

In the words of Red Green:

Remember, it's only temporary... unless it works!

When piping in/out, the REPL is skipped. If something is piping into dt then standard input is fed into dt as a list of lines.

$ echo -e "3\n2\n1" | dt rev pls
1
2
3

$ alias scream-lines="dt [upcase words unlines] map pls"
$ echo "hey you pikachu" | scream-lines
HEY
YOU
PIKACHU

When the first argument to dt is a file starting with #! it will interpret the file. In short: dt supports shebang scripting.

A naive tee implementation:

tee.dt

#!/usr/bin/env dt

read-lines unlines   \stdin :
args pop   \file :

stdin pl
stdin file writef

Then use like:

cat wish-list | sed 's/red/green/g' | tee.dt new-wish-list

Running dt by itself with no pipes in or out starts a read-eval-print loop (REPL).

$ dt
dt 1.x.x
Now, this is only temporary... unless it works.
» # Comments start with #
» 
» 1 1 + println
2
» 
» # Printing is common, so there are a bunch of printing shorthands.
» # "p" is print, "pl" is print line, "pls" is print lines (i.e. of a list of values)
» # Let's define a command that consumes a value, prints it, then returns its double.
» 
» [ \n :   n p " " p   n 2 *] \print-and-double def
» 
» 
» # And let's do it... 7 times!
» 
» 1 \print-and-double 7 times   drop
1 2 4 8 16 32 64
» 
» 
» # You can conditionally execute code
» 
» ["hi" pl] false do?
» ["bye" pl] true do?
bye
» 
» quit

For a best experience, also install rlwrap and set a shell alias like so:

$ alias dtsh='rlwrap dt'
$ dtsh
dt 1.x.x
Now, this is only temporary... unless it works.
» 

The above example assumes a bash-like shell. Details on the syntax and configuration files to set an alias that persists will vary by your shell.

Download assets from releases and put them somewhere on your PATH.

An installation script may come soon.

To build from source, clone the repo and run ./build help for instructions. The project currently builds with Zig 0.11.+ and a recent Cargo toolchain. The resulting binary for your machine will be produced as ./zig-out/bin/dt

⚠️ Most people should skip this section! ⚠️

Certified language nerds only beyond this point, and I will be checking your references! Also, please keep me honest in correctly categorizing the language. The focus is on usefulness more than advancing PLDI, but I'm open to criticism, suggestions, and crazy ideas.

The dt language is in the concatenative language family. That means it's a functional programming language (functions are first-class, values have immutable semantics) with a concatenative style rather than the traditional applicative style.

See also Jon Purdy's Why Concatanative Programming Matters

The dt language has an imperative feel in the sense that all "functions" are linguistically imperative "commands." There is no distinguishing from pure and impure logic; side-effects are allowed and not managed.

For the adept: The language is point-free with opt-in bindings. Everything is evaluated in strict left-to-right sequence, and all operations can have arbitrary arity both in and out, including runtime-dynamic arity. Typing is dynamic, and the language is homoiconic.

It's inspired by many other tools and languages like Unix-style pipes and shells, awk, Forth, Joy, Factor, Haskell, ML, Lisps, Lua, Tcl, Ruby, and Perl. dt does not intended to be better or replace any of these, they're all fantastic and have their place! It's simply meant to be a best tool for different kinds of jobs.

Linguistically, dt command definitions follow a convention of using subject-object-verb (SOV) grammatical order similar to Japanese, Korean, or Latin. (But with much more context elision, even more than Japanese!)

dt is implemented in Zig with no plans to self-host or rewrite in Rust or Go. Please do suggest better strategies for memory management and optimizations! I have some experience working at this level, but still much to learn. The current implementation is still fairly naive.

Shared as open source software, distributed under the terms of the 3-Clause BSD License.

By J.R. Hill | https://so.dang.cool | https://github.com/booniepepper