Expressions.hs

module Expressions where

-- A command which performs something - can be a command that takes arguments
-- or an assignment.
data Cmd = Cmd { name :: Expr -- The command name (can be a variable)
				, args :: [Expr] -- The command arguments
				, inDir :: Maybe Expr -- A redirected input fp
				, outDir :: Maybe Expr -- A redirected output fp
				, append :: Bool -- If redirected, is it appending?
				}
		| Assign { var :: Expr -- Assignment target
				, val :: Expr -- A value to assign to a variable
				}
				deriving Show

-- A bottom-level expression
data Expr = Var String -- A named variable
			| Str String -- A mere string, the peasant of expressions
			deriving (Eq, Show)

-- A comparison operation
data Comp = CEQ Expr Expr -- ==
			| CNE Expr Expr -- /=
			| CGE Expr Expr -- >=
			| CGT Expr Expr -- >
			| CLE Expr Expr -- <=
			| CLT Expr Expr -- <
			| CLI Expr -- A wrapped expression literal - True if nonempty
			deriving (Eq, Show)
-- Something that evaluates to a truth value
data Pred = Pred Comp -- A wrapped comparison
			| Not Pred -- Negation
			| And Pred Pred -- A binary logical and
			| Or Pred Pred -- A binary logical or
			| Parens Pred -- An expression in parentheses
			deriving (Eq, Show)
-- A conditional branching expression - if-then or if-then-else
-- If-then with a condition and a list of actions
data Conditional = If {cond :: Pred -- Predicate to satisfy
						, cthen :: [Cmd] -- Actions if satisfied
						}
-- An if-then-else with a condition and two possible paths
			| IfElse { cond :: Pred -- Predicate to satisfy
						, cthen :: [Cmd] -- Actions if satisfied
						, celse :: [Cmd] -- Actions otherwise
						}
						deriving Show
-- A top-level expression, wrapping either a conditional expression or a
-- command
data TLExpr = TLCmd Cmd
			| TLCnd Conditional
			deriving Show