civicaml/phases/typecheck.ml

open Printf
open Ast
open Util
open Stringify

(*
 * Do a number of checks:
 * x A void function must not return a value.
 * x A non-void function must return a value of the correct type.
 * - Array indices must be of type integer.
 * - The number of array indices must match the number of array dimensions.
 * x The type on the right-hand side of an assignment must match the type on
 *   the left-hand side.
 * - The number of arguments used for a function call must match the number of
 *   parameters for that function.
 * - The types of the function arguments must match the types of parameters.
 * x The operands of a unary or binary operation must have valid types.
 * x The predicate expression of an if, while, or do-while statement must be
 *   a boolean.
 * x Only values having a basic type can be type cast.
 *)

let check_type ?(msg="") expected = function
    | Type (node, got) when got != expected ->
        let msg = match msg with
            | "" -> sprintf "expected type %s, got %s"
                            (type2str expected) (type2str got)
            | _ -> msg
        in
        raise (NodeError (node, msg))
    | Type _ -> ()
    | _ -> raise InvalidNode

let op_types = function
    | Not | And | Or                      -> [Bool]
    | Mod                                 -> [Int]
    | Neg | Sub | Div | Lt | Le | Gt | Ge -> [Int; Float]
    | Add | Mul | Eq | Ne                 -> [Bool; Int; Float]

let op_result_type operand_type = function
    | Not | And | Or | Eq | Ne | Lt | Le | Gt | Ge -> Bool
    | Neg | Add | Sub | Mul | Div | Mod            -> operand_type

(* Check if the given operator can be applied to the given type *)
let check_type_op allowed_types desc = function
    | Type (node, ctype) when not (List.mem ctype allowed_types) ->
        let msg =
            sprintf "%s cannot be applied to type %s, only to %s"
                    desc (type2str ctype) (types2str allowed_types)
        in
        raise (NodeError (node, msg))
    | Type _ -> ()
    | _ -> raise InvalidNode

let rec typecheck node = match node with
    | BoolConst (value, _)    -> Type (node, Bool)
    | IntConst (value, _)     -> Type (node, Int)
    | FloatConst (value, _)   -> Type (node, Float)
    | VarUse (_, ctype, _)    -> Type (node, ctype)
    | FunUse (_, ret_type, _) -> Type (node, ret_type)

    | Monop (op, (Type (_, vtype) as value), _) ->
        let desc = sprintf "unary operator \"%s\"" (op2str op) in
        check_type_op (op_types op) desc value;
        Type (node, op_result_type vtype op)
    | Monop (op, value, loc) ->
        typecheck (Monop (op, typecheck value, loc))

    | Binop (op, (Type (_, ltype) as left), right, loc) ->
        let desc = sprintf "binary operator \"%s\"" (op2str op) in
        check_type_op (op_types op) desc left;
        check_type ltype right;
        Type (node, op_result_type ltype op)
    | Binop (op, left, right, loc) ->
        typecheck (Binop (op, typecheck left, typecheck right, loc))

    | Cond (Type (cond, condtype), Type (texpr, ttype), fexpr, loc) ->
        check_type ttype fexpr;
        Type (node, ttype)

    | VarLet (_, (Type (_, vtype) as value), dec_type, depth) ->
        check_type dec_type value;
        Type (node, vtype)
    | VarLet (assign, value, dec_type, depth) ->
        typecheck (VarLet (assign, typecheck value, dec_type, depth))

    | TypeCast (ctype, (Type _ as value), loc) ->
        check_type_op [Bool; Int; Float] "typecast" value;
        Type (node, ctype)
    | TypeCast (ctype, value, loc) ->
        typecheck (TypeCast (ctype, typecheck value, loc))

    | Return (Type _, _) ->
        node
    | Return (value, loc) ->
        typecheck (Return (typecheck value, loc))

    | FunDef (export, ret_type, name, params, body, loc) ->
        let params = transform_all typecheck params in
        let body = typecheck body in
        let rec find_return = function
            | []                                   -> None
            | [Return (Type (_, rtype), _) as ret] -> Some (ret, rtype)
            | hd :: tl                             -> find_return tl
        in (
        match (ret_type, find_return (block_body body)) with
            | (Void, Some (ret, _)) ->
                raise (NodeError (ret, "void function should not have a return value"))
            | ((Bool | Int | Float), None) ->
                let msg =
                    sprintf "expected return value of type %s for function \"%s\""
                            (type2str ret_type) name
                in
                raise (NodeError (node, msg))
            | ((Bool | Int | Float), Some (ret, t)) when t != ret_type ->
                let msg =
                    sprintf "function \"%s\" has return type %s, got %s"
                            name (type2str ret_type) (type2str t)
                in
                raise (NodeError (ret, msg))
            | _ ->
                FunDef (export, ret_type, name, params, body, loc)
        )

    (* Conditions in if-statements and loop must be type bool *)
    | If (Type _ as cond, _, _)
    | IfElse (Type _ as cond, _, _, _)
    | While (Type _ as cond, _, _)
    | DoWhile (Type _ as cond, _, _) ->
        check_type Bool cond (*~msg:"condition should have type bool"*);
        node
    | If (cond, body, loc) ->
        typecheck (If (typecheck cond, typecheck body, loc))
    | IfElse (cond, tbody, fbody, loc) ->
        typecheck (IfElse (typecheck cond, typecheck tbody, typecheck fbody, loc))
    | While (cond, body, loc) ->
        typecheck (While (typecheck cond, typecheck body, loc))
    | DoWhile (cond, body, loc) ->
        typecheck (DoWhile (typecheck cond, typecheck body, loc))

    | _ -> transform_children typecheck node

let rec phase input =
    prerr_endline "- Type checking";
    match input with
    | Ast (node, args) ->
        Ast (typecheck node, args)
    | _ -> raise (InvalidInput "typecheck")