refactor: PgArg to ProcParam

Clarify the difference between arguments and parameters.
Parameters are part of the function definition, arguments are the values
passed to the function.

Also clarify the findProc function comments and error message.

src/PostgREST/DbStructure/Proc.hs

@@ -2,16 +2,16 @@
 {-# LANGUAGE DeriveGeneric  #-}
 
 module PostgREST.DbStructure.Proc
-  ( PgArg(..)
-  , PgType(..)
+  ( PgType(..)
   , ProcDescription(..)
+  , ProcParam(..)
   , ProcVolatility(..)
   , ProcsMap
   , RetType(..)
   , procReturnsScalar
   , procReturnsSingle
   , procTableName
-  , specifiedProcArgs
+  , specifiedProcParams
   ) where
 
 import qualified Data.Aeson          as JSON
@@ -24,15 +24,6 @@ import PostgREST.DbStructure.Identifiers (FieldName,
 
 import Protolude
 
-
-data PgArg = PgArg
-  { pgaName :: Text
-  , pgaType :: Text
-  , pgaReq  :: Bool
-  , pgaVar  :: Bool
-  }
-  deriving (Eq, Ord, Generic, JSON.ToJSON)
-
 data PgType
   = Scalar
   | Composite QualifiedIdentifier
@@ -53,19 +44,27 @@ data ProcDescription = ProcDescription
   { pdSchema      :: Schema
   , pdName        :: Text
   , pdDescription :: Maybe Text
-  , pdArgs        :: [PgArg]
+  , pdParams      :: [ProcParam]
   , pdReturnType  :: RetType
   , pdVolatility  :: ProcVolatility
   , pdHasVariadic :: Bool
   }
   deriving (Eq, Generic, JSON.ToJSON)
 
--- Order by least number of args in the case of overloaded functions
+data ProcParam = ProcParam
+  { ppName :: Text
+  , ppType :: Text
+  , ppReq  :: Bool
+  , ppVar  :: Bool
+  }
+  deriving (Eq, Ord, Generic, JSON.ToJSON)
+
+-- Order by least number of params in the case of overloaded functions
 instance Ord ProcDescription where
-  ProcDescription schema1 name1 des1 args1 rt1 vol1 hasVar1 `compare` ProcDescription schema2 name2 des2 args2 rt2 vol2 hasVar2
-    | schema1 == schema2 && name1 == name2 && length args1 < length args2  = LT
-    | schema2 == schema2 && name1 == name2 && length args1 > length args2  = GT
-    | otherwise = (schema1, name1, des1, args1, rt1, vol1, hasVar1) `compare` (schema2, name2, des2, args2, rt2, vol2, hasVar2)
+  ProcDescription schema1 name1 des1 prms1 rt1 vol1 hasVar1 `compare` ProcDescription schema2 name2 des2 prms2 rt2 vol2 hasVar2
+    | schema1 == schema2 && name1 == name2 && length prms1 < length prms2  = LT
+    | schema2 == schema2 && name1 == name2 && length prms1 > length prms2  = GT
+    | otherwise = (schema1, name1, des1, prms1, rt1, vol1, hasVar1) `compare` (schema2, name2, des2, prms2, rt2, vol2, hasVar2)
 
 -- | A map of all procs, all of which can be overloaded(one entry will have more than one ProcDescription).
 -- | It uses a HashMap for a faster lookup.
@@ -75,9 +74,9 @@ type ProcsMap = M.HashMap QualifiedIdentifier [ProcDescription]
   Search the procedure parameters by matching them with the specified keys.
   If the key doesn't match a parameter, a parameter with a default type "text" is assumed.
 -}
-specifiedProcArgs :: S.Set FieldName -> ProcDescription -> [PgArg]
-specifiedProcArgs keys proc =
-  (\k -> fromMaybe (PgArg k "text" True False) (find ((==) k . pgaName) (pdArgs proc))) <$> S.toList keys
+specifiedProcParams :: S.Set FieldName -> ProcDescription -> [ProcParam]
+specifiedProcParams keys proc =
+  (\k -> fromMaybe (ProcParam k "text" True False) (find ((==) k . ppName) (pdParams proc))) <$> S.toList keys
 
 procReturnsScalar :: ProcDescription -> Bool
 procReturnsScalar proc = case proc of