[#5] Write some README (#14)

* [#5] Write some README

Resolves #5

* Update src/PgNamed.hs

Co-Authored-By: Dmitrii Kovanikov <[email protected]>

* Update README.md

Co-Authored-By: Dmitrii Kovanikov <[email protected]>

* Update README.md

Co-Authored-By: Dmitrii Kovanikov <[email protected]>

* Update README.md

Co-Authored-By: Dmitrii Kovanikov <[email protected]>

* Fix after review

Author: vrom911

README.md

@@ -1,12 +1,70 @@
 # postgresql-simple-named
 
+[![Build status](https://img.shields.io/travis/Holmusk/postgresql-simple-named.svg?logo=travis)](https://travis-ci.org/Holmusk/postgresql-simple-named)
 [![Hackage](https://img.shields.io/hackage/v/postgresql-simple-named.svg?logo=haskell)](https://hackage.haskell.org/package/postgresql-simple-named)
-[![MPL-2.0 license](https://img.shields.io/badge/license-MPL--2.0-blue.svg)](LICENSE)
 [![Stackage Lts](http://stackage.org/package/postgresql-simple-named/badge/lts)](http://stackage.org/lts/package/postgresql-simple-named)
 [![Stackage Nightly](http://stackage.org/package/postgresql-simple-named/badge/nightly)](http://stackage.org/nightly/package/postgresql-simple-named)
-[![Build status](https://img.shields.io/travis/Holmusk/postgresql-simple-named.svg?logo=travis)](https://travis-ci.org/Holmusk/postgresql-simple-named)
+[![MPL-2.0 license](https://img.shields.io/badge/license-MPL--2.0-blue.svg)](LICENSE)
+
+This library introduces the implementation of named parameters for the
+[`postgresql-simple`][pgs] library. `postgresql-simple-named` is considered to
+be used along with the [`postgresql-simple`][pgs] library, so you could refer
+there for the original documentation of primary functions. This package solves
+exclusively one particular problem — gives the ability to use named parameters
+instead of `?` in quasi-quoter queries and offers essential functions for substituting
+variables in queries (`queryNamed`, `executeNamed`).
+
+## Example
+
+Operator `=?` binds named parameters with the corresponding values. Named
+parameters inside SQL query start with the '?' character and can contain
+lowercase and uppercase letters, digits and underscore. Below you can find a
+basic example of how query with named parameters could look like:
+
+```haskell
+queryNamed dbConnection [sql|
+    SELECT
+        id, name, city
+    FROM users
+    WHERE name = ?nameParam
+      AND age  = ?ageParam
 
-Implementation of named parameters for `postgresql-simple` library
+|] [ "nameParam" =? "John"
+   , "ageParam"  =? 42
+   ]
+```
+
+This feature can be extremely helpful when the query uses some parameters more than once:
+
+```haskell
+query dbConnection [sql|
+    SELECT
+        col1, col2
+    FROM my_table
+    WHERE id = ?
+      AND (? IS NULL OR id > ? )
+      AND (? IS NULL OR id < ? )
+
+|] (someId, minId, minId, maxId, maxId)
+```
+
+This is how the query looks like with the `postgresql-simple` library. You can
+rewrite it the following way using the `postgresql-simple-named` library:
+
+```haskell
+queryNamed dbConnection [sql|
+    SELECT
+        col1, col2
+    FROM my_table
+    WHERE id = ?someId
+      AND (?minId IS NULL OR id > ?minId )
+      AND (?maxId IS NULL OR id < ?maxId )
+
+|] [ "someId" =? 42
+   , "minId"  =? 1
+   , "maxId"  =? 100
+   ]
+```
 
 ## How to build
 
@@ -19,3 +77,6 @@ Build the library with either `cabal new-build` or `stack build`.
   docker run -p 5432\:5432 -e POSTGRES_USER=postgres -e POSTGRES_DB=pg_named postgres\:10.5-alpine
   ```
 * Run tests using `cabal new-test` or `stack test`
+
+
+[pgs]: https://hackage.haskell.org/package/postgresql-simple

postgresql-simple-named.cabal

@@ -3,7 +3,7 @@ name:                postgresql-simple-named
 version:             0.0.0.0
 synopsis:            Implementation of named parameters for `postgresql-simple` library
 description:
-    Implementation of named parameters for `postgresql-simple` library.
+    Implementation of named parameters for @postgresql-simple@ library.
     .
     Here is an exaple of how it could be used in your code:
     .
@@ -21,8 +21,8 @@ homepage:            https://github.com/Holmusk/postgresql-simple-named
 bug-reports:         https://github.com/Holmusk/postgresql-simple-named/issues
 license:             MPL-2.0
 license-file:        LICENSE
-author:              Holmusk
-maintainer:          Holmusk<[email protected]>
+author:              Dmitrii Kovanikov, Veronika Romashkina
+maintainer:          Holmusk <[email protected]>
 copyright:           2019 Holmusk
 category:            Database
 build-type:          Simple

src/PgNamed.hs

@@ -4,18 +4,19 @@
 
 {- | Introduces named parameters for @postgresql-simple@ library.
 It uses @?@ question mark symbol as the indicator of the named parameter which
-is replaced with the standard syntax with question marks. Check out the example
-of usage:
+is replaced with the standard syntax with question marks.
+
+Check out the example of usage:
 
 @
-queryNamed [sql|
+'queryNamed' [sql|
     SELECT *
     FROM users
     WHERE foo = ?foo
       AND bar = ?bar
       AND baz = ?foo
-|] [ "foo" =? "fooBar"
-   , "bar" =? "barVar"
+|] [ "foo" '=?' "fooBar"
+   , "bar" '=?' "barVar"
    ]
 @
 -}
@@ -28,6 +29,7 @@ module PgNamed
 
          -- * Errors
        , PgNamedError (..)
+       , WithNamedError
 
          -- * Functions to deal with named parameters
        , extractNames
@@ -71,15 +73,15 @@ data NamedParam = NamedParam
 data PgNamedError
     -- | Named parameter is not specified.
     = PgNamedParam Name
-    -- | Query has no names inside but was called with named functions,
+    -- | Query has no names inside but was called with named functions.
     | PgNoNames PG.Query
     -- | Query contains an empty name.
     | PgEmptyName PG.Query
   deriving (Eq)
 
 
 -- | Type alias for monads that can throw errors of the 'PgNamedError' type.
-type WithError = MonadError PgNamedError
+type WithNamedError = MonadError PgNamedError
 
 instance Show PgNamedError where
     show e = "PostgreSQL named parameter error: " ++ case e of
@@ -99,8 +101,8 @@ lookupName n = lookup n . map (\NamedParam{..} -> (namedParamName, namedParamPar
 SELECT name, user FROM users WHERE id = ?id
 @
 
-and returns either the error or query with all all names replaced by
-questiosn marks @?@ with list of the names in the order of their appearance.
+and returns either the error or the query with all names replaced by
+question marks @?@ with the list of the names in the order of their appearance.
 
 For example:
 
@@ -132,9 +134,11 @@ extractNames qr = go (PG.fromQuery qr) >>= \case
     isNameChar c = isAlphaNum c || c == '_'
 
 
--- | Returns the list of values to use in query by given list of 'Name's.
+{- | Returns the list of values to use in query by given list of 'Name's.
+Throws 'PgNamedError' if any named parameter is not specified.
+-}
 namesToRow
-    :: forall m . WithError m
+    :: forall m . WithNamedError m
     => NonEmpty Name  -- ^ List of the names used in query
     -> [NamedParam]   -- ^ List of the named parameters
     -> m (NonEmpty PG.Action)
@@ -176,7 +180,7 @@ queryNamed dbConnection [sql|
 @
 -}
 queryNamed
-    :: (MonadIO m, WithError m, PG.FromRow res)
+    :: (MonadIO m, WithNamedError m, PG.FromRow res)
     => PG.Connection  -- ^ Database connection
     -> PG.Query       -- ^ Query with named parameters inside
     -> [NamedParam]   -- ^ The list of named parameters to be used in the query
@@ -197,7 +201,7 @@ executeNamed dbConnection [sql|
 @
 -}
 executeNamed
-    :: (MonadIO m, WithError m)
+    :: (MonadIO m, WithNamedError m)
     => PG.Connection  -- ^ Database connection
     -> PG.Query       -- ^ Query with named parameters inside
     -> [NamedParam]   -- ^ The list of named parameters to be used in the query
@@ -208,7 +212,7 @@ executeNamed conn qNamed params =
 
 -- | Helper to use named parameters.
 withNamedArgs
-    :: WithError m
+    :: WithNamedError m
     => PG.Query
     -> [NamedParam]
     -> m (PG.Query, NonEmpty PG.Action)