I want write a haskell program to implement a simple imperative language based on its denotational semantics. I use GHCi, version 8.4.2 on windows. I encountered some issue when implementing function and procedure abstraction described below.
let me describe it. I call it IMP. First, I define abstract syntax. IMP only accept integer. and identifier will be string.
type Numeral = Int
type Ident = String
data Command =
Skip
| Assign (Ident, Expression)
| Letin (Declaration, Command )
| Cmdcmd (Command, Command )
| Ifthen (Expression, Command, Command)
| Whiledo (Expression, Command )
| IdentifierC ( ActualParameter )
data Expression =
Num Numeral
| False_
| True_
| Notexp Expression
| Id Ident
| Sumof (Expression, Expression)
| Subof (Expression, Expression)
| Prodof (Expression, Expression)
| Less (Expression, Expression)
| Leten (Declaration, Expression)
| IdentifierE ( ActualParameter )
deriving Show
type ActualParameter = Expression
data FormalParameter = Constfp Identifier
data Declaration =
Constdef (Ident, Expression)
| Vardef (Ident, TypeDef )
| Func Identifier ( FormalParameter ) ~ Expression
| Proce Identifier ( FormalParameter ) ~ Command
deriving Show
data TypeDef =
Bool | Int
deriving Show
brief explanation: in Command, Skip will do nothing. Assign will give value of the Expression to the Ident. Letin will declare some variable in command. Cmdcmd will run 2 commands sequentially. Ifthen is conditional command, if first expression is evaluated to true, then run first command, second command otherwise. Whiledo is loop. IdentifierC ( ActualParameter ): IdentifierC denotes some function in the local environment. this ActualParameter is some expression with some value. this command jus call this function on the specified value.
in Expression, from top to down are: numeral bool false bool true negate of expression get value of the Ident from the local environment. sum 2 expressions substract 2 expressions product of 2 < declare some variable in expression IdentifierE ( ActualParameter ) IdentifierE denotes some function in the local environment. this ActualParameter is some expression with some value. this command jus call this function on the specified value. finally got a new value as the result of this expression.
then is Semantic Domains
type Integer = Int
type Boolean = Bool
type Location = Int
type Function = Argument -> Store -> Value
type Procedure = Argument -> Store -> Store
-- store would be snapshot of the memory.
data Value = IntValue Int
| TruthValue Bool
deriving (Eq, Show)
-- first class value only are int and bool
type Storable = Value
data Bindable = Const Value
| Variable Location
| Function Func
| Procedure Proce
deriving (Eq, Show)
data Denotable = Unbound | Bound Bindable
deriving (Eq, Show)
type Argument = Value
data Sval = Stored Storable | Undef | Unused
-- The actual storage in a Store
type DataStore = Location -> Sval
-- --bot--- --top--- --data---
data Store = Store (Location, Location, DataStore)
type Environ = Ident -> Denotable
-- ---------- Semantic Functions -------------- --
valuation :: Int -> Value
evaluate :: Expression -> Environ -> Store -> Value
elaborate :: Declaration -> Environ -> Store -> (Environ,Store)
execute :: Command -> Environ -> Store -> Store
-- the main goal is to define these semantic functions
-- I give some examples in my source code below.
my code is here: https://github.com/sanyuwen/IMP/blob/master/DSemImp.hs. my test code is here: https://github.com/sanyuwen/IMP/blob/master/ImpTest.hs
when I use GHC to import DSemImp module, I encountered many errors.
DSemImp.hs:52:32: error:
Not in scope: type constructor or class ‘Identifier’
|
52 | data FormalParameter = Constfp Identifier | ^^^^^^^^^^
It said data FormalParameter = Constfp Identifier is not legal.
without this how can I define formal parameter ??
You didn't define Identifier. Though you defined Ident, is that what you meant?