ArchLang

A floor plan DSL ​

ArchLang is an open-source language for floor plans, created by Chan Meng: you write .arch text and compile it to SVG, DXF or PDF.

It is a domain-specific language (DSL): it describes buildings and nothing else. A plan is a plan "…" { … } block of statements such as wall, room, door, window, furniture, dim and stair, measured in millimetres from a top-left origin. On top of those statements it has a small programming layer — variables, functions, loops and conditionals — that runs while the drawing is built and then disappears.

Variables and loops in a floor plan ​

Three studio units in a row, generated by a for loop from three constants and an array of names:

arch
plan "Studio row" {
  units mm
  grid 50
  let W = 4000
  let H = 5000
  let names = ["Studio A", "Studio B", "Studio C"]

  for i in 0..3 {
    let x = i * W
    wall exterior thickness 200 { (x, 0) (x + W, 0) (x + W, H) (x, H) close }
    room at (x, 0) size W x H label "{names[i]}" uses living
    door at (x + W / 2, H) width 900 wall exterior hinge left swing in
    window at (x + W / 2, 0) width 1600 wall exterior
  }
}

The loop expands into three walls, three rooms, three doors and three windows before anything is drawn. Change W and every unit, door and window moves. npx -y @chanmeng666/archlang describe on this source reports three rooms of 20 m² each, 60 m² in all, and lint reports no warnings.

What is in the language ​

  • Elements: walls (straight or arc), rooms (rectangles, polygons, circles), doors, windows, openings, furniture and fixtures with real plan symbols, dimensions, columns, stairs, lifts, roofs, voids, outdoor areas, fences, a title block and a room schedule.
  • Placement by relation: a room right-of another, walls derived from rooms, a door between two rooms, furniture against a wall. See relational placement.
  • Scripting: let bindings, value functions, arrays and ranges, string interpolation, for/if/while, set defaults and reusable components. It expands at compile time: there is no runtime, no I/O and no clock (ADR 3).
  • Several storeys with level blocks, compiled to one drawing per storey.
  • Checks: describe reads a compiled plan back as facts (rooms, areas, adjacency, what each door connects); lint gives advisory warnings such as a bedroom with no window or a bathroom reached only through a bedroom. See Analysis.

The language reference covers every statement, and the one-page spec states the whole language in a form short enough for a model's system prompt.

Bounded and deterministic ​

Every input compiles within a fixed step budget and a fixed drawing budget, so a runaway loop is reported as a diagnostic instead of hanging. The compiler takes no input from the environment, so the same source gives the same SVG byte for byte. Errors come back as diagnostics with a code, a line and column, and a suggested fix; the error catalog lists them all.

Tooling for the language ​

bash
npx -y @chanmeng666/archlang spec                  # print the whole language on one page
npx -y @chanmeng666/archlang compile plan.arch -o plan.svg
npx -y @chanmeng666/archlang fmt plan.arch         # format the source
npx -y @chanmeng666/archlang manifest --json       # every command and flag, as data
  • A VS Code extension (code --install-extension ChanMeng.archlang) adds highlighting, live diagnostics, completion, hover, go to definition and quick fixes.
  • A GBNF grammar (/archlang.gbnf) constrains a local model to emit parseable source, and a JSON schema (/plan.schema.json) describes the Plan JSON input that compile --from-json accepts.

FAQ ​

Is there a programming language for floor plans? ​

ArchLang is one. A .arch file declares walls, rooms, doors and windows in millimetres, and the compiler draws them as an SVG, DXF or PDF floor plan. It also has variables, functions and loops for generating repeated or parametric layouts.

Is ArchLang a general-purpose programming language? ​

No. Its scripting forms (let, functions, for, if, while) exist to generate plan statements. They expand at compile time, cannot read files or the clock, and run within a fixed step budget.

How is a floor plan DSL different from drawing in CAD? ​

A CAD drawing stores lines and shapes; an ArchLang plan stores rooms, walls and doors as named things with relations. That lets the compiler report areas, adjacency and reachability, and lets a change to one number move everything that depends on it. ArchLang exports DXF when the drawing has to continue in CAD.

Where is the full grammar? ​

The language reference documents every statement and clause, the one-page spec summarises it, and /archlang.gbnf is the grammar in GBNF form.

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