TOML Parser
This package implements a validating parser for TOML 1.0.0.
This package uses an alex-generated
lexer and happy-generated parser.
It also provides a pair of classes for serializing into and out of TOML.
Package Structure
---
title: Package Structure
---
stateDiagram-v2
classDef important font-weight:bold;
TOML:::important --> ApplicationTypes:::important : decode
ApplicationTypes --> TOML : encode
TOML --> [Token]: Toml.Lexer
[Token] --> [Expr]: Toml.Parser
[Expr] --> Table : Toml.Semantics
Table --> ApplicationTypes : Toml.FromValue
ApplicationTypes --> Table : Toml.ToValue
Table --> TOML : Toml.Pretty
The highest-level interface to this package is to define FromValue
and ToTable
instances for your application-specific datatypes. These can be used with encode
and decode
to convert to and from TOML.
For low-level access to the TOML format, the lexer, parser, and validator are available
for direct use. The diagram above shows how the different modules enable you to
advance through the increasingly high-level TOML representations.
Example
Consider this sample TOML text from the specification.
[[fruits]]
name = "apple"
[fruits.physical] # subtable
color = "red"
shape = "round"
[[fruits.varieties]] # nested array of tables
name = "red delicious"
[[fruits.varieties]]
name = "granny smith"
[[fruits]]
name = "banana"
[[fruits.varieties]]
name = "plantain"
Parsing using this package generates the following value
>>> Right fruitToml = parse fruitStr
>>> fruitToml
Right (fromList [
("fruits",Array [
Table (fromList [
("name",String "apple"),
("physical",Table (fromList [
("color",String "red"),
("shape",String "round")])),
("varieties",Array [
Table (fromList [("name",String "red delicious")]),
Table (fromList [("name",String "granny smith")])])]),
Table (fromList [
("name",String "banana"),
("varieties",Array [
Table (fromList [("name",String "plantain")])])])])])
We can render this parsed value back to TOML text using prettyToml fruitToml
.
In this case the input was already sorted, so the generated text will happen
to match almost exactly.
Here's an example of defining datatypes and deserializers for the TOML above.
newtype Fruits = Fruits [Fruit]
deriving (Eq, Show)
data Fruit = Fruit String (Maybe Physical) [Variety]
deriving (Eq, Show)
data Physical = Physical String String
deriving (Eq, Show)
newtype Variety = Variety String
deriving (Eq, Show)
instance FromValue Fruits where
fromValue = parseTableFromValue (Fruits <$> reqKey "fruits")
instance FroValue Fruit where
fromValue = parseTableFromValue (Fruit <$> reqKey "name" <*> optKey "physical" <*> reqKey "varieties")
instance FromValue Physical where
fromValue = parseTableFromValue (Physical <$> reqKey "color" <*> reqKey "shape")
instance FromValue Variety where
fromValue = parseTableFromValue (Variety <$> reqKey "name")
We can run this example on the original value to deserialize it into domain-specific datatypes.
>>> decode fruitToml :: Either String Fruits
Right (Fruits [
Fruit "apple" (Just (Physical "red" "round")) [Variety "red delicious", Variety "granny smith"],
Fruit "banana" Nothing [Variety "plantain"]])
Generics
Code for generating and matching tables to records can be derived
using GHC.Generics. This will generate tables using the field names
as table keys.
data ExampleRecord = ExampleRecord {
exString :: String,
exList :: [Int],
exOpt :: Maybe Bool}
deriving (Show, Generic, Eq)
instance FromValue ExampleRecord where fromValue = parseTableFromValue genericParseTable
instance ToTable ExampleRecord where toTable = genericToTable
instance ToValue ExampleRecord where toValue = defaultTableToValue
Larger Example
A demonstration of using this package at a more realistic scale
can be found in HieDemoSpec.