I have a data type called EntrySearchableInfo
written like this
type EntryDate = UTCTime -- From Data.Time
type EntryTag = Tag -- String
type EntryName = Name -- String
type EntryDescription = Description -- String
type EntryId = Int
data EntrySearchableInfo
= SearchableEntryDate EntryDate
| SearchableEntryTag EntryTag
| SearchableEntryName EntryName
| SearchableEntryDescription EntryDescription
| SearchableEntryId EntryId
Basically represents things that make sense in 'search' context.
I want to write a function with this type
entrySearchableInfoParser :: Parser (Either String EntrySearchableInfo)
which (I think) will be a combination of several primitive Parser <Type>
functions I have already written
entryDateParser :: Parser (Either String UTCTime)
entryDateParser = parseStringToUTCTime <$> strOption
(long "date" <> short 'd' <> metavar "DATE" <> help entryDateParserHelp)
searchableEntryDateParser :: Parser (Either String EntrySearchableInfo)
searchableEntryDateParser = SearchableEntryDate <$$> entryDateParser -- <$$> is just (fmap . fmap)
searchableEntryTagParser :: Parser (Either String EntrySearchableInfo)
searchableEntryTagParser = ...
...
So I have two questions:
How do I combine those parsers to make entrySearchableInfoParser
functions.
EntrySearchableInfo
type is a part of a larger Entry
type defined like this
data Entry
= Add EntryDate EntryInfo EntryTag EntryNote EntryId
| Replace EntrySearchableInfo Entry
| ...
...
I already have a function with type
entryAdd :: Parser (Either String Entry)
which constructs Entry
using Add
.
But I'm not sure how to make Entry
type using Replace
with entrySearchableInfoParser
and entryAdd
.
So combining those parsers were a lot simpler than I imagined.
I just had to use <|>
entrySearchableInfoParser :: Parser (Either String EntrySearchableInfo)
entrySearchableInfoParser =
searchableEntryDateParser
<|> searchableEntryTagParser
<|> searchableEntryNameParser
<|> searchableEntryDescriptionParser
<|> searchableEntryIdParser
and constructing Entry
type using Replace
with entrySearchableInfoParser
and entryAdd
was too.
entryAdd :: Parser (Either String Entry)
entryAdd = ...
entryReplace :: Parser (Either String Entry)
entryReplace = liftA2 Edit <$> entrySearchableInfoParser <*> entryAdd
Now it works perfectly!