nushell/crates/nu-source/README.md
Ryan Blecher 23d11d5e84 Nu source overview (#1282)
* add some notes into README for more elaboration

* rewrite the overview

* remove unused first line

* add last part about tracing and debugging

* change the wording to make it easier to read

* Add example of metadata system

* Add contact information as other helpful links
2020-01-27 15:55:02 +13:00

1.6 KiB

nu-source

Overview

The nu-source crate contains types and traits used for keeping track of metadata about values being processed. Nu uses Tags to keep track of where a value came from, an AnchorLocation, as well as positional information about the value, a Span. An AchorLocation can be a Url, File, or Source text that a value was parsed from. The source Text is special in that it is a type similar to a String that comes with the ability to be cheaply cloned. A Span keeps track of a value's start and end positions. These types make up the metadata for a value and are wrapped up together in a Tagged struct, which holds everything needed to track and locate a value.

Nu's metadata system can be seen when reporting errors. In the following example Nu is able to report to the user where the typo of a column originated from.

1 | ls | get typ
  |          ^^^ did you mean 'type'?

In addition to metadata tracking, nu-source also contains types and traits related to debugging, tracing, and formatting the metadata and values it processes.

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