180 lines
7.2 KiB
OCaml
180 lines
7.2 KiB
OCaml
module Utility = Utility
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open Types;;
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Random.self_init ()
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let (let*) = Result.bind
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let rec evaluate_type (program: t_exp) (context: ftype VariableMap.t) : (ftype, error) result =
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match program with
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Integer _ -> Ok IntegerType
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| Boolean _ -> Ok BooleanType
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| Variable x -> ( (* check for the type in the context *)
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match VariableMap.find_opt x context with
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None -> Error (`AbsentAssignment
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("The variable " ^ x ^ " is not defined."))
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| Some t -> Ok t
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)
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| Function (xs, typef, fbody) -> (
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(* first check that the function has the right specified type then check
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that the number of inputs are the right number, finally eval the type
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of the body using the bindings for the inputs *)
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match typef with
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FunctionType (tin, tout) -> (
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if List.length xs <> List.length tin then
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Error (`WrongTypeSpecification
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("Type specification for function has wrong arity."))
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else
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let context1 = List.fold_left2
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(fun acc x t -> VariableMap.add x t acc)
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context
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xs
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tin
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in
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let* typefbody = evaluate_type fbody context1 in
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if (typefbody = tout) then
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Ok typef
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else
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Error (`WrongTypeSpecification
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("Function does not return specified type."))
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)
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| _ -> Error (`WrongTypeSpecification
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("Specification of function is not a function type."))
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)
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| Application (f, xs) -> (
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(* check that the type is actually a function, then checks that the
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supplied inputs are of the right type, returns the return type if all
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inputs are supplied, otherwise a function from the remaining inputs to
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the output types *)
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let* evalf = evaluate_type f context in
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match evalf with
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FunctionType (tin, tout) -> (
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let rec helper (params: t_exp list) (typeparams: ftype list) =
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(* consumes until params are exausted *)
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match (params, typeparams) with
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([], _) -> Ok typeparams
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| (_, []) -> Error (`WrongArity ("Function application has arity " ^
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(List.length tin |> string_of_int) ^
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", but was applied to " ^
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(List.length xs |> string_of_int) ^
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" parameters"))
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| (p::tlparams, v::tltypeparams) ->
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if evaluate_type p context = Ok v then
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helper tlparams tltypeparams
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else
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Error (`WrongType "Argument with wrong type.")
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in
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let* typesremaining = helper xs tin in
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match typesremaining with
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[] -> Ok tout
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| t -> Ok (FunctionType (t, tout))
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)
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| _ -> Error (`WrongType "Applying to a non function type")
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)
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| Plus (x, y)
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| Minus (x, y)
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| Times (x, y)
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| Division (x, y)
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| Modulo (x, y)
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| Power (x, y) -> (
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let* typex = evaluate_type x context in
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let* typey = evaluate_type y context in
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match typex, typey with
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| (IntegerType, IntegerType) -> Ok IntegerType
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| (IntegerType, _) -> Error (`WrongType "Second term is not an integer.")
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| (_, _) -> Error (`WrongType "First term is not an integer.")
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)
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| PowerMod (x, y, z) -> (
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let* typex = evaluate_type x context in
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let* typey = evaluate_type y context in
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let* typez = evaluate_type z context in
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match typex, typey, typez with
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| (IntegerType, IntegerType, IntegerType) -> Ok IntegerType
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| (IntegerType, IntegerType, _) -> Error (`WrongType ("Third term is " ^
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"not an integer."))
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| (IntegerType, _, _) -> Error (`WrongType
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("Second term is not an integer."))
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| (_, _, _) -> Error (`WrongType "First term is not an integer.")
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)
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| Rand (x) -> (
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let* typex = evaluate_type x context in
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match typex with
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| (IntegerType) -> Ok IntegerType
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| (_) -> Error (`WrongType "Term is not an integer.")
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)
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| BAnd (x, y)
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| BOr (x, y) -> (
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let* typex = evaluate_type x context in
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let* typey = evaluate_type y context in
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match typex, typey with
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| (BooleanType, BooleanType) -> Ok BooleanType
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| (BooleanType, _) -> Error (`WrongType "Second term is not a boolean.")
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| (_, _) -> Error (`WrongType "First term is not a boolean.")
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)
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| BNot (x) -> (
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let* typex = evaluate_type x context in
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match typex with
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| (BooleanType) -> Ok BooleanType
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| (_) -> Error (`WrongType "Term is not a boolean.")
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)
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| Cmp (x, y)
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| CmpLess (x, y)
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| CmpLessEq (x, y)
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| CmpGreater (x, y)
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| CmpGreaterEq (x, y) -> (
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let* typex = evaluate_type x context in
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let* typey = evaluate_type y context in
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match typex, typey with
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| (IntegerType, IntegerType) -> Ok BooleanType
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| (IntegerType, _) -> Error (`WrongType "Second term is not an integer.")
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| (_, _) -> Error (`WrongType "First term is not an integer.")
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)
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| IfThenElse (guard, if_exp, else_exp) -> (
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let* typeguard = evaluate_type guard context in
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let* typeif_exp = evaluate_type if_exp context in
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let* typeelse_exp = evaluate_type else_exp context in
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match typeguard, typeif_exp, typeelse_exp with
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(BooleanType, t1, t2) -> (
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if t1 = t2 then
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Ok t1
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else
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Error (`WrongType "If branches do not have the same type.")
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)
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| (_, _, _) -> Error (`WrongType "If guard is not a boolean.")
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)
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| LetIn (x, xval, rest) ->
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(* bind the type to the variable name in the context *)
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let* typex = evaluate_type xval context in
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evaluate_type rest (VariableMap.add x typex context)
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| LetFun (f, xs, typef, fbody, rest) ->
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(* like with the function type, but also add f itself to the bindings *)
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match typef with
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FunctionType (tin, tout) -> (
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if List.length xs <> List.length tin then
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Error (`WrongArity "Type specification for function has wrong arity.")
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else
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let context1 = VariableMap.add f typef context in
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let context2 = List.fold_left2
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(fun acc x t -> VariableMap.add x t acc)
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context1
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xs
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tin
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in
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let* typefbody = evaluate_type fbody context2 in
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let* typerest = evaluate_type rest context1 in
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match (typefbody = tout, typerest) with
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(false, _) -> Error (`WrongTypeSpecification
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"Function does not return specified type.")
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| (true, t) -> Ok t
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)
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| _ -> Error (`WrongTypeSpecification
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"Specification of function is not a function type.")
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let typecheck (program: t_exp) : (ftype, error) result =
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let* typeprogram = evaluate_type program VariableMap.empty in
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match typeprogram with
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FunctionType ([IntegerType], IntegerType) -> (
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Ok (FunctionType ([IntegerType], IntegerType))
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)
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| _ -> Error (`WrongType "Program is not a function from int to int.")
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