-- | A symbol identifier following the format [a-z][a-zA-Z0-9_-]*
type Identifier = Text

-- | 'AST's encode the various types of expressions in the language.
data AST = ASTValue | ASTExpression deriving (Show, Eq)

data ASTConjunction = ASTAnd [AST] | ASTOr [AST] deriving (Show, Eq)

data ASTValue = ASTRoot [AST] -- ^ A series of sub-ASTs
         | ASTLiteral Value -- ^ A literal that does not require evaluation
         | ASTFunc Identifier [ASTValue]
         -- ^ A function call and list of arguments
         | ASTVar Identifier -- ^ Variable dereference
         | ASTIndex ASTValue [Identifier] -- ^ Nested index into an object
         | ASTArray (V.Vector ASTValue)
         -- ^ A literal array (may contain non-literals)
         deriving (Show, Eq)

data ASTExpression = ASTIf ASTConjunction ASTValue (Maybe ASTValue)
         -- ^ If - condition, true branch and optional false branch
         | ASTFor (Maybe Identifier) Identifier ASTValue ASTValue (Maybe ASTValue)
         -- ^ for([k,]v in expr) body separator
  deriving (Show, Eq)