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also update the README with the toplevel printers documentation

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Anil Madhavapeddy 2019-01-31 10:37:01 +00:00
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README.md
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@ -206,6 +206,34 @@ correctly:
It shall point to the directory `stublibs` inside your ocaml installation.
Automatically installing toplevel printers
------------------------------------------
Utop will automatically install toplevel printers for custom
types if their interface file is marked with an
`[@@ocaml.toplevel_printer]` attribute. Adding this annotation to
your libraries will remove the need to have a separate `top` package
to install the printers.
For example, in the [uri](https://github.com/mirage/ocaml-uri)
library, the old printing function for `Uri.t` was:
```
val pp_hum : Format.formatter -> t -> unit
```
Just adding this annotation results in `Uri.t` values being automatically
pretty printed in this version of utop.
```
val pp_hum : Format.formatter -> t -> unit [@@ocaml.toplevel_printer]
```
There should be no downsides to adding this attribute to your
libraries, so we encourage community library maintainers to
use this attribute to improve the out-of-the-box experience
for users of their libraries within utop.
Creating a custom utop-enabled toplevel
---------------------------------------