This module builds on http://hackage.haskell.org/package/cassava to provide support for simpler mapping of records to and from CSV.

This is primarily achieved by use of modern GHC features such as HasField and OverloadedLabels.

Defining a record

First, we define a record with which we want to map to and from our csv data

data TestItem = TestItem
 { field1 :: Int
 , field2 :: SomeItem
 , field3 :: String
 } deriving Generic

Declaring a CsvMapped instance

The class provides a CsvMap, which is a list of either:

• A bidirectional mapping from header to field selector, or
• The field selector of a record (also implementing CsvMapped to nest

Each mapping can be mapped in either direction using the Profunctor instance functions lmap to map encoding, rmap to map decoding, or dimap for both. Refer to examples to see this in practice.

instance CsvMapped TestItem where
 csvMap = mkCsvMap
   [ "Field 1" := #field1
   , #field2
   , "Field 3" := #field3
   ]

instance CsvMapped SomeItem where ...

Encoding and decoding

The encode and decode functions will infer our CsvMapped type and perform the mapping. Type applications may be needed on decode depending on the use context.

To encode to csv:

encode WithHeader testItems

To decode from csv:

decode @TestItem WithHeader csvByteString