A TRAC-64 interpreter — the text-processing language invented by Calvin Mooers in 1964 and presented as an etude by Charles Wetherell in Etudes for Programmers (1978).

Every TRAC program is a macro expansion over a shared string: function calls are written #(name,arg1,arg2,…), the innermost call is evaluated first, its result is substituted back into the containing string, and the scanner re-reads from that point. Two call modes: #(…) rescans the result (active), ##(…) appends it literally (neutral).

The interpreter is written in TypeScript. It implements the full TRAC-64 primitive set from the book plus two extensions suggested there: forms can be called directly by name (#(myform,x) ≡ #(cl,myform,x)), and user-defined forms can shadow builtins.

Not implemented: external stream I/O (ai, ao, sp, rp) and external block storage (sb, fb, eb). These return "N/A".

All functions are covered by unit tests.

Try it in the browser: https://begoon.github.io/trac/ — editor, example dropdown, and a Run button. Code is saved to localStorage.

Globally, as a CLI:

npx trac64i

TRAC interpreter (CTRL-C or #(hl)' to exit)

TRAC> #(ps,hello)'hello
TRAC>

Or run directly from a checkout of this repository — node (24+), bun, or deno can all execute trac.ts without a build step.

The commands below are run from a checkout of the repository; substitute trac64i for node trac.ts if you installed the CLI globally.

node trac.ts examples/e.trac

2.7182818277

node trac.ts examples/pi.trac

3.1415926538

node trac.ts examples/factorial.trac

30414093201713378043612608166064768844377641568960512000000000000

node trac.ts examples/hanoi.trac

from 1 to 3
from 1 to 2
from 3 to 2
from 1 to 3
from 2 to 1
from 2 to 3
from 1 to 3

node trac.ts examples/rule_110.trac

...............1...............
..............11...............
.............111...............
............11.1...............
...........11111...............
..........11...1...............
.........111..11...............
........11.1.111...............
.......1111111.1...............
......11.....111...............
.....111....11.1...............

Command-line arguments prefixed with @ are treated as inline TRAC programs instead of file paths:

node trac.ts "@#(ps,I am TRAC)'"

I am TRAC

node trac.ts

TRAC interpreter (CTRL-C or #(hl)' to exit)

TRAC>

Implemented primitives, grouped:

• Forms — ds (define), ss (segment with markers), cl (call), ln (list names), da (delete all), dd (delete).
• Form pointer / segmentation — cs (call segment), cc (call character), cn (call N chars), in (call-in / find), cr (call restore, and radix change when arity is 3), pf (print form), sr (segment-rank).
• Arithmetic (bigint) — ad, su, ml, dv.
• Boolean (bit strings) — bu (union), bi (intersection), bc (complement), bs (shift), br (rotate).
• Comparison — eq, gr.
• I/O — ps (print string), rs (read string), rc (read character).
• Character / meta — cd (char→decimal codepoint), dc (decimal→char), sl (string length), cm (change meta), qm (query meta).
• Tracing — tn (trace on), tf (trace off), hl (halt).

See info/trac.pdf for Wetherell's etude description and info/cowan/ for supplementary material.

bun install

just test         # run the test suite (81 cases)
just build        # tsc -> dist/
just build-docs   # refresh docs/trac.js from the build (playground)
just publish      # patch version + npm publish (maintainer only)

MIT — see LICENSE.