1 files changed, 78 insertions, 36 deletions

diff --git a/src/Language/SimpleShell/AST.hs b/src/Language/SimpleShell/AST.hs
index 7549626..5a222c3 100644
--- a/src/Language/SimpleShell/AST.hs
+++ b/src/Language/SimpleShell/AST.hs
@@ -1,24 +1,22 @@
 {-# LANGUAGE GADTs #-}
-{-# LANGUAGE TypeSynonymInstances #-}
-{-# LANGUAGE FlexibleInstances #-}
-{-# LANGUAGE MultiParamTypeClasses #-}
 
 module Language.SimpleShell.AST
 where
 
-class SimpleType a
-instance SimpleType Integer
-instance SimpleType String
-instance SimpleType Bool
+data SimpleType a where
+  IntType :: SimpleType Integer
+  StringType :: SimpleType String
+  BoolType :: SimpleType Bool
 
-class Castable a b
-instance Castable Integer String
-instance Castable String Integer
+data SimpleTypeList a where
+  NilTs :: SimpleTypeList ()
+  ConsTs :: SimpleType a -> SimpleTypeList as -> SimpleTypeList (a, as)
 
+-- | Pure expression (no side effects).
 data Expr a where
-  Literal :: (SimpleType a) => a -> Expr a
+  Literal :: SimpleType a -> a -> Expr a
   VarE :: Var a -> Expr a
-  FunctionCall :: Function a args -> ExprList args -> Expr a
+  FunctionCall :: FunctionRef a args -> ExprList args -> Expr a
   And :: Expr Bool -> Expr Bool -> Expr Bool
   Or  :: Expr Bool -> Expr Bool -> Expr Bool
   Not :: Expr Bool -> Expr Bool
@@ -28,35 +26,79 @@ data Expr a where
   Ge  :: Expr Integer -> Expr Integer -> Expr Bool
   Lt  :: Expr Integer -> Expr Integer -> Expr Bool
   Le  :: Expr Integer -> Expr Integer -> Expr Bool
-  Ternary :: (SimpleType a) => Expr Bool -> Expr a -> Expr a -> Expr a
-  Cast :: (Castable a b) => Expr a -> Expr b
+  Ternary :: Expr Bool -> Expr a -> Expr a -> Expr a
+  Length :: Expr String -> Expr Integer
+  StrToInt :: Expr String -> Expr Integer
+  IntToStr :: Expr Integer -> Expr String
+
+data FunctionRef a args = FunctionRef String
+
+data Function a args
+  = Function
+      (Args args)
+      (Expr a)
+
+data Function' where
+  Function'
+    :: SimpleType a
+    -> SimpleTypeList as
+    -> Function a as
+    -> Function'
 
 data ExprList a where
   NilE :: ExprList ()
   ConsE :: Expr a -> ExprList as -> ExprList (a, as)
 
-data Var a where
-  Var :: (SimpleType a) => String -> Var a
+data Var a = Var (SimpleType a) String
+
+data Var' where
+  Var' :: Var a -> Var'
 
 data Args args where
   NilArgs :: Args ()
-  ConsArgs :: (SimpleType a) => Var a -> Args as -> Args (a, as)
-
-data Statement a where
-  Declare :: Var a -> Statement b
-  Assign :: Var a -> Expr a -> Statement b
-  Print :: Expr String -> Statement b
-  Command
-    :: (Maybe (Var Integer))  -- shell return value
-    -> (Maybe (Var String))   -- stdout
-    -> (Maybe (Var String))   -- stderr
-    -> Command a
-    -> Statement a
-  Return :: Expr a -> Statement a
-
-data Command a where
-  ExtCmd :: Expr String -> [Expr String] -> Command b
-  CompundCmd :: [Statement a] -> Command a
-
-data Function a args where
-  Function :: (SimpleType a) => Args args -> Command a -> Function a args
+  ConsArgs :: Var a -> Args as -> Args (a, as)
+
+data Statement ret
+  = AssignExpr ExprAssignment'
+  | Print (Expr String)
+  | PrintErr (Expr String)
+  | If (Expr Bool) [Statement ret] [Statement ret]
+  | While (Expr Bool) [Statement ret]
+  | RunCommand
+      (Maybe (Var Integer))  -- shell return value
+      (Maybe (Var String))   -- stdout
+      (Maybe (Var String))   -- stderr
+      (Command ret)
+  | RunProcedure ProcAssignment'
+  | Return (Expr ret)
+
+data ExprAssignment' where
+  ExprAssignment' :: Var a -> Expr a -> ExprAssignment'
+
+data ProcAssignment' where
+  ProcAssignment'
+    :: Maybe (Var a)        -- procedure return value
+    -> Maybe (Var String)   -- stdout
+    -> Maybe (Var String)   -- stderr
+    -> ProcRef a args
+    -> Args args
+    -> ProcAssignment'
+
+data Command ret
+  = ExtCmd (Expr String) [Expr String]
+  | CompoundCmd [Statement ret]
+
+data Procedure ret args
+  = Procedure
+      (Args args)
+      [Var']    -- ^ variable declarations
+      (Command ret)
+
+data ProcRef ret args = ProcRef String
+
+data Procedure' where
+  Procedure'
+    :: SimpleType ret
+    -> SimpleTypeList args
+    -> Procedure ret args
+    -> Procedure'