Query.hs

module Grakn.Query
  ( IsQuery(queryString)
  , MatchQuery
  , match
  , select
  , limit
  , distinct
  ) where

import           Grakn.Pattern
import           Grakn.Property
import           Grakn.Util

class IsQuery q where
  queryString :: q -> String

-- |A Graql 'match' query that finds a pattern in the graph
data MatchQuery
  = Match [Pattern]
  | Select MatchQuery
           [Var]
  | Limit MatchQuery
          Integer
  | Distinct MatchQuery

-- |Create a match query by providing a list of patterns
match :: Convert a Pattern => [a] -> MatchQuery
match = Match . map convert

-- |Select variables from a match query, intended to be used infix
select :: [Var] -> MatchQuery -> MatchQuery
select = flip Select

-- |Limit a match query, intended to be used infix
limit :: Integer -> MatchQuery -> MatchQuery
limit = flip Limit

-- |Retrieve only distinct results from a match query
distinct :: MatchQuery -> MatchQuery
distinct = Distinct

instance Show MatchQuery where
  show (Match patts)    = "match " ++ spaces patts
  show (Select mq vars) = show mq ++ " select " ++ commas vars ++ ";"
  show (Limit mq lim)   = show mq ++ " limit " ++ show lim ++ ";"
  show (Distinct mq)    = show mq ++ " distinct;"

instance IsQuery MatchQuery where
  queryString = show

instance IsQuery String where
  queryString = id