Port of https://github.com/tscircuit/stepts to MoonBit

cad

step

modeling

moon add gmlewis/step@0.1.16

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Author

gmlewis

Version

0.1.16

License

Apache-2.0

Repository

github.com/gmlewis/moonbit-step

Last updated

3 days ago

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Dependencies

README

#gmlewis/step (MoonBit)

A high-level 3D modeling DSL and lossless STEP (ISO 10303-21) parser/serializer in MoonBit.

This repo allows you to build 3D models using a simple API and export them to valid, topologically-sound STEP files.

Onshape design: https://cad.onshape.com/documents/b8320fedf1f1ea6028755ae8/w/50dfab2e1185c97711b860a6/e/20263eabe6f1f22cc85a5a09?renderMode=0&uiState=695414a99e93423471a30e60

Example 12: The Bifilar Electromagnet, an invention of mine with interesting electrical properties.

#Quick Start (Modeling)

Building a model is intuitive:

async fn main {
  let design = @cad.Design::new(name="my-model")
    .add(
      @cad.Cuboid::new(20, 20, 20)
        .with_name("base")
        .with_color(@cad.Rgb::orange())
    )
    .add(
      @cad.CalibrationChamferBlock::new(10, 10, 5, chamfer_size_mm=1.0)
        .with_name("top-part")
        .translate(z=20)
    )

  design.write_step(Some("model.step"))
}

#Exporting to Blender (Python)

This repo can generate Blender 5.0 Python scripts that recreate your model with correct physical scale. The generated script uses meters (Blender’s default), while your CAD dimensions remain in millimeters.

#From your own model

Implement your design in MoonBit (see the modeling example above).
Emit Blender Python instead of STEP:

design.write_blender_python(Some("model.py"))

Open Blender and run the script from the Scripting workspace, or run Blender directly from the command line:

blender --background --factory-startup --python model.py

#From the included examples

Generate Blender scripts and ".blend" files for all examples:

./scripts/manage_examples.py all --bpy

This produces .py and .blend files in bpy-out. Each script removes the default cube (if present), recreates the model, and selects all created geometry.

#Quick Start (Parsing)

Parsing from a string:

fn parse_example(step_text : String) -> Unit {
  match @parse.parse_repository_from_string_result(step_text) {
    @parse.ParseRepositoryResult::Ok(repo) => {
      let normalized = repo.to_step_file()
      println("entities=" + repo.len().to_string())
      println(normalized)
    }
    @parse.ParseRepositoryResult::Err(info) =>
      @cli.eprintln(@parse.format_step_parse_error(info))
  }
}

#Features

Fluent 3D DSL: Chain transformations like .translate(), .with_color(), and .with_name().
Lossless Roundtrips: Unknown/unmodeled entities are preserved during parse/serialize cycles.
Robust CLI: Built-in validation, proper stderr reporting, and short-circuiting exit codes.
Deterministic: Serializer output is stable (parse → serialize → parse is idempotent).

#Development & Validation

#Verification

Run the unit tests and formatters:

./test-all.sh

#Geometric Validation & Rendering

We use Open CASCADE (occt-draw or DRAWEXE) to ensure topological validity and generate previews:

./scripts/manage_examples.py all --validate --render --readme

#Goals

Provide a pleasant authoring UX for 3D models in MoonBit.
Parse real-world STEP files without panicking.
Provide actionable parse errors (line/col + statement snippets).

#License

Apache-2.0

#Status

The code has been updated to support compiler:

$ moon version --all
moon 0.1.20260807 (4da23f8 2026-08-07) ~/.moon/bin/moon
moonc v0.10.7+bc794d341 (2026-08-11) ~/.moon/bin/moonc
moonrun 0.1.20260807 (4da23f8 2026-08-07) ~/.moon/bin/moonrun

#
Entity

source

pub(open) trait Entity {
  fn to_step(Self) -> String
}

#
EntityId

source

pub(all) struct EntityId {
  value : Int
}

#
RawEntity

source

pub struct RawEntity {
  name : String
  args : String
}

impl Entity for RawEntity

#
RawEntity::new

source

fn RawEntity::new(name : String, args : String) -> RawEntity

#
Ref

source

pub(all) struct Ref {
  id : EntityId
}

#
UnknownEntity

source

pub struct UnknownEntity {
}

#
fmt_num

source

fn fmt_num(n : Double) -> String

#
step_str

source

fn step_str(s : String) -> String

#
unknown_entity_witness

source

let unknown_entity_witness : UnknownEntity

Source Files

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step

#gmlewis/step (MoonBit)

#Quick Start (Modeling)

#Exporting to Blender (Python)

#From your own model

#From the included examples

#Quick Start (Parsing)

#Features

#Development & Validation

#Verification

#Geometric Validation & Rendering

#Goals

#License

#Status

#Entity

#EntityId

#RawEntity

#RawEntity::new

#Ref

#UnknownEntity

#fmt_num

#step_str

#unknown_entity_witness

Source Files

#
Entity

#
EntityId

#
RawEntity

#
RawEntity::new

#
Ref

#
UnknownEntity

#
fmt_num

#
step_str

#
unknown_entity_witness