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About

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Literate Programming (LP) is a form of programming focused on creating documents of interleaved prose, code, and supporting diagrams/illustrations, pioneered by Donald Knuth for his TeX system. If you're new to this approach, please first read the Wikipedia article for a basic introduction. For all LP projects, a so-called "tangling" step is required to produce workable, standard source code files from these documents. This package provides just that:

Extract, expand, transclude, combine and assemble code blocks from arbitrary text files into actual/traditional source code files. The following input formats are supported:

  • Markdown
  • Markdown codeblocks embedded inside docstrings of JavaScript/TypeScript source files
  • Org-mode

A single input file can contain code for multiple languages. Each individual code block can define its own target file and include noweb-style references to other code blocks, either from the same or even from other files. If multiple code blocks in the same input file reference the same output file, they will be concatenated.

The package provides both a basic API and a CLI wrapper to perform the "tangling" tasks (an expression borrowed from Org-mode).

(FWIW all early thi.ng libraries created between 2011-2016 were written in this format, e.g. thi.ng/fabric, thi.ng/geom, thi.ng/luxor, thi.ng/morphogen)

Document front matter

LP source files can contain a front matter section, currently supporting the following properties (all optional, also see example document further below):

tangle

Absolute or relative path to base output directory for tangled code blocks. This is only used if a code block's tangle path is a relative path.

publish

Absolute or relative path to write a "published" version of the LP source file, in which all code blocks have been transformed & code block references resolved/expanded/transcluded. If this property is omitted, no such output will be generated.

Code block metadata

In addition to the optional document front matter configuration, each code block can specify the following metadata key:value pairs:

id

Unique (within the current doc) code block identifier. Only required if the contents of this code block are to be referenced/transcluded elsewhere.

noweb

If set to noweb:no, any code block references in this block will not be expanded. See section below for more details about these reference.

publish

If set to publish:no, the code block will be omitted in the published version of the current document.

tangle

Absolute or relative path of the target file where the expanded contents of this code block should be written to. If a relative path, it'll be relative to the path stated in the front matter. If omitted, the code block will not be extracted to its own file. If multiple code blocks in the same source file are specifying the same target file, their contents will be concatenated (in order of appearance).

Basic usage

The following Markdown example acts as a source file (presumably for Literate Programming purposes) from which various interlinked code blocks will be extracted (into any number of new files). Additionally, this file itself is also being transformed for "publishing", meaning all code block references & transclusions are getting resolved/replaced in the published version of this file.

main.md:

---
publish: out/main.md
tangle: out
---
# Tangle test

This next code block will be tangled/extracted to the specified file and since
its body entirely consists of a reference to another code block, it will be
replaced with the contents of the code block with ID `imports` in the file
`lib.md` (see further below)

```ts tangle:src/index.ts
<<lib.md#imports>>
```

Next we transclude the contents of the code block with ID `foo` and perform some
other computation. This block (and the next one too) will be tangled to the same
target file (concatenated):

```ts tangle:src/index.ts
<<foo>>

const bar = 42;

console.log(foo + bar);
```

Finally, here's a demonstration of how transcluded code blocks can also receive
parameters (supplied via an options object as argument):

```ts tangle:src/index.ts
<<lib.md#parametric { "hello": "world" }>>
```

## Misc

The following block will be only transcluded in the first one, however has its
`publish` flag disabled so that it will **not** be included in the published
version of this file.

```ts id:foo publish:no
const foo = 23;
```

lib.md (e.g. maybe a library of useful snippets for a larger project):

# Library of snippets

```ts id:imports
// @ts-ignore
import type { Fn } from "@thi.ng/api";
```

```ts id:parametric
export const hello = "Hi, {{hello}}!";
```

Calling the tangle CLI util, we can process these example files and produce the following two outputs:

npx @thi.ng/tangle --help

#  █ █   █           │
# ██ █               │
#  █ █ █ █   █ █ █ █ │ @thi.ng/tangle 0.1.0
#  █ █ █ █ █ █ █ █ █ │ Literate programming code block tangling
#                  █ │
#                █ █ │
#
# usage: tangle [OPTS] SOURCE-FILES(S) ...
#        tangle --help
#
# Flags:
#
# -d, --debug         enable debug output
# --dry-run           enable dry run (don't overwrite files)
# --no-comments       don't generate comments
npx @thi.ng/tangle main.md
# [INFO] tangle: writing file: <...>/out/src/index.ts
# [INFO] tangle: writing file: <...>/out/main.md

Generated Outputs

The generated/tangled source file: out/src/index.ts

// Tangled @ 2022-09-21T16:57:43+02:00 - DO NOT EDIT!
// Source: <...>/main.lit.md

// @ts-ignore
import type { Fn } from "@thi.ng/api";

const foo = 23;

const bar = 42;

console.log(foo + bar);

export const hello = "Hi, world!";

The published version of the input markdown file: out/main.md

---
publish: out/main.md
tangle: out
---
# Tangle test

This next code block will be tangled/extracted to the specified file and since
its body entirely consists of a reference to another code block, it will be
replaced with the contents of the code block with ID `imports` in the file
`lib.md` (see further below)

```ts
// @ts-ignore
import type { Fn } from "@thi.ng/api";
```

Next we transclude the contents of the code block with ID `foo` and perform some
other computation. This block (and the next one too) will be tangled to the same
target file (concatenated):

```ts
const foo = 23;

const bar = 42;

console.log(foo + bar);
```

Finally, here's a demonstration of how transcluded code blocks can also receive
parameters (supplied via an options object as argument):

```ts
export const hello = "Hi, world!";
```

## Misc

The following block will be only transcluded in the first one, however has its
`publish` flag disabled so that it will **not** be included in the published
version of this file.

Editor integrations

VSCode

Using the Run On Save extension, tangling can be automatically performed on each save of an Literate Programming source file. E.g. this configuration (add to your VSCode workspace settings.json) runs the tangle command on each save of a *.lit.md file.

"emeraldwalk.runonsave": {
    "commands": [
        {
            "match": "\\.lit\\.md$",
            "cmd": "${workspaceFolder}/node_modules/.bin/tangle ${file}"
        }
    ]
}

Note: This also assumes you have this package (@thi.ng/tangle) added to your dependencies...

Other editors

Accepting PRs with instructruction for other editors & IDEs.

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Installation

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Dependencies

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API

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In addition to the CLI wrapper, the package provides the tangleFile() and tangleString() functions. See /test/index.ts for usage examples.