unison/unison-src/transcripts/docs.md

Documenting Unison code

.> builtins.merge

Unison documentation is written in Unison. Documentation is a value of the following type:

.> view builtin.Doc

You can create these Doc values with ordinary code, or you can use the special syntax. A value of type Doc can be created via syntax like:

use .builtin

doc1 = [: This is some documentation.

It can span multiple lines.

Can link to definitions like @List.drop or @List

:]

Syntax:

[: starts a documentation block; :] finishes it. Within the block:

• Links to definitions are done with @List. \@ (and \:]) if you want to escape.
• @[signature] List.take expands to the type signature of List.take
• @[source] List.map expands to the full source of List.map
• @[include] someOtherDoc, inserts a value someOtherDoc : Doc here.
• @[evaluate] someDefinition expands to the result of evaluating someDefinition, which must be a pre-existing definition in the codebase (can't be an arbitrary expression).

An example

We are going to document List.take using some verbiage and a few examples. First we have to add the examples to the codebase:

List.take.ex1 = take 0 [1,2,3,4,5]
List.take.ex2 = take 2 [1,2,3,4,5]

.> add

And now let's write our docs and reference these examples:

use .builtin

docs.List.take = [:
`@List.take n xs` returns the first `n` elements of `xs`. (No need to add line breaks manually. The display command will do wrapping of text for you.  Indent any lines where you don't want it to do this.)

## Examples:

  @[source] List.take.ex1
  🔽
  @List.take.ex1 = @[evaluate] List.take.ex1


  @[source] List.take.ex2
  🔽
  @List.take.ex2 = @[evaluate] List.take.ex2
:]

Let's add it to the codebase, and link it to the definition:

.> add
.> link docs.List.take builtin.List.take

Now that documentation is linked to the definition. We can view it if we like:

.> links builtin.List.take builtin.Doc
.> display 1

Or there's also a convenient function, docs, which shows the Doc values that are linked to a definition. It's implemented in terms of links and display:

.> docs builtin.List.take

Note that if we view the source of the documentation, the various references are not expanded.

.> view docs.List.take