How deeply does Learn Haskell by Example cover field?

Defines the type and demonstrates repeated use, but stops short of implementing FieldParser.

Field

As explained in Learn Haskell by Example

field is a sqlite-simple function that creates a RowParser for a value whose type has a FromField instance.

field creates a RowParser for one database-column value when its type has a FromField instance. FromField supplies a FieldParser, while RowParser combines parsers for complete rows. section 16.3.2

Use field repeatedly with applicative operators to build a FromRow parser. Each field consumes the next column and converts it to the requested Haskell type. section 16.3.2

Parsing a TodoEntry row

instance FromRow TodoEntry where fromRow = TodoEntry <$> field <*> field <*> field <*> field A query can then return [TodoEntry], with each field parser handling one selected column.

How Learn Haskell by Example covers it

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Related concepts

recordpart of · A record is a structured data unit or type that groups related values into fields or properties, typically to represent one item, entity, or observation.
executeNamedused by · executeNamed is a sqlite-simple function that executes an SQL statement using named parameters supplied from a Haskell value.
attributeuses · An attribute is a named property, value, or piece of information associated with an entity, object, or program element.

This explainer was generated by Manning's knowledge graph from the text of Learn Haskell by Example. The section links point to the parts of the book it draws on.