(* This file is part of the Catala compiler, a specification language for tax and social benefits computation rules. Copyright (C) 2022 Inria, contributor: Aymeric Fromherz Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. *) open Utils open Dcalc open Ast open Z3 module StringMap : Map.S with type key = String.t = Map.Make (String) type context = { ctx_z3 : Z3.context; (* The Z3 context, used to create symbols and expressions *) ctx_decl : decl_ctx; (* The declaration context from the Catala program, containing information to precisely pretty print Catala expressions *) ctx_var : typ Marked.pos VarMap.t; (* A map from Catala variables to their types, needed to create Z3 expressions of the right sort *) ctx_funcdecl : FuncDecl.func_decl VarMap.t; (* A map from Catala function names (represented as variables) to Z3 function declarations, used to only define once functions in Z3 queries *) ctx_z3vars : Var.t StringMap.t; (* A map from strings, corresponding to Z3 symbol names, to the Catala variable they represent. Used when to pretty-print Z3 models when a counterexample is generated *) ctx_z3datatypes : Sort.sort EnumMap.t; (* A map from Catala enumeration names to the corresponding Z3 sort, from which we can retrieve constructors and accessors *) ctx_z3matchsubsts : Expr.expr VarMap.t; (* A map from Catala temporary variables, generated when translating a match, to the corresponding enum accessor call as a Z3 expression *) ctx_z3structs : Sort.sort StructMap.t; (* A map from Catala struct names to the corresponding Z3 sort, from which we can retrieve the constructor and the accessors *) ctx_z3unit : Sort.sort * Expr.expr; (* A pair containing the Z3 encodings of the unit type, encoded as a tuple of 0 elements, and the unit value *) ctx_z3constraints : Expr.expr list; (* A list of constraints about the created Z3 expressions accumulated during their initialization, for instance, that the length of an array is an integer which always is greater than 0 *) } (** The context contains all the required information to encode a VC represented as a Catala term to Z3. The fields [ctx_decl] and [ctx_var] are computed before starting the translation to Z3, and are thus unmodified throughout the translation. The [ctx_z3] context is an OCaml abstraction on top of an underlying C++ imperative implementation, it is therefore only created once. Unfortunately, the maps [ctx_funcdecl], [ctx_z3vars], and [ctx_z3datatypes] are computed dynamically during the translation requiring us to pass the context around in a functional way **) (** [add_funcdecl] adds the mapping between the Catala variable [v] and the Z3 function declaration [fd] to the context **) let add_funcdecl (v : Var.t) (fd : FuncDecl.func_decl) (ctx : context) : context = { ctx with ctx_funcdecl = VarMap.add v fd ctx.ctx_funcdecl } (** [add_z3var] adds the mapping between [name] and the Catala variable [v] to the context **) let add_z3var (name : string) (v : Var.t) (ctx : context) : context = { ctx with ctx_z3vars = StringMap.add name v ctx.ctx_z3vars } (** [add_z3enum] adds the mapping between the Catala enumeration [enum] and the corresponding Z3 datatype [sort] to the context **) let add_z3enum (enum : EnumName.t) (sort : Sort.sort) (ctx : context) : context = { ctx with ctx_z3datatypes = EnumMap.add enum sort ctx.ctx_z3datatypes } (** [add_z3var] adds the mapping between temporary variable [v] and the Z3 expression [e] representing an accessor application to the context **) let add_z3matchsubst (v : Var.t) (e : Expr.expr) (ctx : context) : context = { ctx with ctx_z3matchsubsts = VarMap.add v e ctx.ctx_z3matchsubsts } (** [add_z3struct] adds the mapping between the Catala struct [s] and the corresponding Z3 datatype [sort] to the context **) let add_z3struct (s : StructName.t) (sort : Sort.sort) (ctx : context) : context = { ctx with ctx_z3structs = StructMap.add s sort ctx.ctx_z3structs } let add_z3constraint (e : Expr.expr) (ctx : context) : context = { ctx with ctx_z3constraints = e :: ctx.ctx_z3constraints } (** For the Z3 encoding of Catala programs, we define the "day 0" as Jan 1, 1900 **) let base_day = CalendarLib.Date.make 1900 1 1 (** [unique_name] returns the full, unique name corresponding to variable [v], as given by Bindlib **) let unique_name (v : 'm var) : string = Format.asprintf "%s_%d" (Bindlib.name_of v) (Bindlib.uid_of v) (** [date_to_int] translates [date] to an integer corresponding to the number of days since Jan 1, 1900 **) let date_to_int (d : Runtime.date) : int = (* Alternatively, could expose this from Runtime as a (noop) coercion, but would allow to break abstraction more easily elsewhere *) let date : CalendarLib.Date.t = CalendarLib.Printer.Date.from_string (Runtime.date_to_string d) in let period = CalendarLib.Date.sub date base_day in CalendarLib.Date.Period.nb_days period (** [date_of_year] translates a [year], represented as an integer into an OCaml date corresponding to Jan 1st of the same year *) let date_of_year (year : int) = Runtime.date_of_numbers year 1 1 (** Returns the date (as a string) corresponding to nb days after the base day, defined here as Jan 1, 1900 **) let nb_days_to_date (nb : int) : string = CalendarLib.Printer.Date.to_string (CalendarLib.Date.add base_day (CalendarLib.Date.Period.day nb)) (** [print_z3model_expr] pretty-prints the value [e] given by a Z3 model according to the Catala type [ty], corresponding to [e] **) let rec print_z3model_expr (ctx : context) (ty : typ Marked.pos) (e : Expr.expr) : string = let print_lit (ty : typ_lit) = match ty with (* TODO: Print boolean according to current language *) | TBool -> Expr.to_string e (* TUnit is only used for the absence of an enum constructor argument. Hence, when pretty-printing, we print nothing to remain closer from Catala sources *) | TUnit -> "" | TInt -> Expr.to_string e | TRat -> Arithmetic.Real.to_decimal_string e !Cli.max_prec_digits (* TODO: Print the right money symbol according to language *) | TMoney -> let z3_str = Expr.to_string e in (* The Z3 model returns an integer corresponding to the amount of cents. We reformat it as dollars *) let to_dollars s = Runtime.money_to_string (Runtime.money_of_cents_string s) in if String.contains z3_str '-' then Format.asprintf "-%s $" (to_dollars (String.sub z3_str 3 (String.length z3_str - 4))) else Format.asprintf "%s $" (to_dollars z3_str) (* The Z3 date representation corresponds to the number of days since Jan 1, 1900. We pretty-print it as the actual date *) (* TODO: Use differnt dates conventions depending on the language ? *) | TDate -> nb_days_to_date (int_of_string (Expr.to_string e)) | TDuration -> Format.asprintf "%s days" (Expr.to_string e) in match Marked.unmark ty with | TLit ty -> print_lit ty | TTuple (_, Some name) -> let s = StructMap.find name ctx.ctx_decl.ctx_structs in let get_fieldname (fn : StructFieldName.t) : string = Marked.unmark (StructFieldName.get_info fn) in let fields = List.map2 (fun (fn, ty) e -> Format.asprintf "-- %s : %s" (get_fieldname fn) (print_z3model_expr ctx ty e)) s (Expr.get_args e) in let fields_str = String.concat " " fields in Format.asprintf "%s { %s }" (Marked.unmark (StructName.get_info name)) fields_str | TTuple (_, None) -> failwith "[Z3 model]: Pretty-printing of unnamed structs not supported" | TEnum (_tys, name) -> (* The value associated to the enum is a single argument *) let e' = List.hd (Expr.get_args e) in let fd = Expr.get_func_decl e in let fd_name = Symbol.to_string (FuncDecl.get_name fd) in let enum_ctrs = EnumMap.find name ctx.ctx_decl.ctx_enums in let case = List.find (fun (ctr, _) -> String.equal fd_name (Marked.unmark (EnumConstructor.get_info ctr))) enum_ctrs in Format.asprintf "%s (%s)" fd_name (print_z3model_expr ctx (snd case) e') | TArrow _ -> failwith "[Z3 model]: Pretty-printing of arrows not supported" | TArray _ -> (* For now, only the length of arrays is modeled *) Format.asprintf "(length = %s)" (Expr.to_string e) | TAny -> failwith "[Z3 model]: Pretty-printing of Any not supported" (** [print_model] pretty prints a Z3 model, used to exhibit counter examples where verification conditions are not satisfied. The context [ctx] is useful to retrieve the mapping between Z3 variables and Catala variables, and to retrieve type information about the variables that was lost during the translation (e.g., by translating a date to an integer) **) let print_model (ctx : context) (model : Model.model) : string = let decls = Model.get_decls model in Format.asprintf "%a" (Format.pp_print_list ~pp_sep:(fun fmt () -> Format.fprintf fmt "\n") (fun fmt d -> if FuncDecl.get_arity d = 0 then (* Constant case *) match Model.get_const_interp model d with (* TODO: Better handling of this case *) | None -> failwith "[Z3 model]: A variable does not have an associated Z3 solution" (* Print "name : value\n" *) | Some e -> let symbol_name = Symbol.to_string (FuncDecl.get_name d) in let v = StringMap.find symbol_name ctx.ctx_z3vars in Format.fprintf fmt "%s %s : %s" (Cli.with_style [ANSITerminal.blue] "%s" "-->") (Cli.with_style [ANSITerminal.yellow] "%s" (Bindlib.name_of (Var.get v))) (print_z3model_expr ctx (VarMap.find v ctx.ctx_var) e) else (* Declaration d is a function *) match Model.get_func_interp model d with (* TODO: Better handling of this case *) | None -> failwith "[Z3 model]: A variable does not have an associated Z3 solution" (* Print "name : value\n" *) | Some f -> let symbol_name = Symbol.to_string (FuncDecl.get_name d) in let v = StringMap.find symbol_name ctx.ctx_z3vars in Format.fprintf fmt "%s %s : %s" (Cli.with_style [ANSITerminal.blue] "%s" "-->") (Cli.with_style [ANSITerminal.yellow] "%s" (Bindlib.name_of (Var.get v))) (* TODO: Model of a Z3 function should be pretty-printed *) (Model.FuncInterp.to_string f))) decls (** [translate_typ_lit] returns the Z3 sort corresponding to the Catala literal type [t] **) let translate_typ_lit (ctx : context) (t : typ_lit) : Sort.sort = match t with | TBool -> Boolean.mk_sort ctx.ctx_z3 | TUnit -> fst ctx.ctx_z3unit | TInt -> Arithmetic.Integer.mk_sort ctx.ctx_z3 | TRat -> Arithmetic.Real.mk_sort ctx.ctx_z3 | TMoney -> Arithmetic.Integer.mk_sort ctx.ctx_z3 (* Dates are encoded as integers, corresponding to the number of days since Jan 1, 1900 *) | TDate -> Arithmetic.Integer.mk_sort ctx.ctx_z3 | TDuration -> Arithmetic.Integer.mk_sort ctx.ctx_z3 (** [translate_typ] returns the Z3 sort correponding to the Catala type [t] **) let rec translate_typ (ctx : context) (t : typ) : context * Sort.sort = match t with | TLit t -> ctx, translate_typ_lit ctx t | TTuple (_, Some name) -> find_or_create_struct ctx name | TTuple (_, None) -> failwith "[Z3 encoding] TTuple type of unnamed struct not supported" | TEnum (_, e) -> find_or_create_enum ctx e | TArrow _ -> failwith "[Z3 encoding] TArrow type not supported" | TArray _ -> (* For now, we are only encoding the (symbolic) length of an array. Ultimately, the type of an array should also contain its elements *) ctx, Arithmetic.Integer.mk_sort ctx.ctx_z3 | TAny -> failwith "[Z3 encoding] TAny type not supported" (** [find_or_create_enum] attempts to retrieve the Z3 sort corresponding to the Catala enumeration [enum]. If no such sort exists yet, it constructs it by creating a Z3 constructor for each Catala constructor of [enum], and adds it to the context *) and find_or_create_enum (ctx : context) (enum : EnumName.t) : context * Sort.sort = (* Creates a Z3 constructor corresponding to the Catala constructor [c] *) let create_constructor (ctx : context) (c : EnumConstructor.t * typ Marked.pos) : context * Datatype.Constructor.constructor = let name, ty = c in let name = Marked.unmark (EnumConstructor.get_info name) in let ctx, arg_z3_ty = translate_typ ctx (Marked.unmark ty) in (* The mk_constructor_s Z3 function is not so well documented. From my understanding, its argument are: - a string corresponding to the name of the constructor - a recognizer as a symbol corresponding to the name (unsure why) - a list of symbols corresponding to the arguments of the constructor - a list of types, that must be of the same length as the list of arguments - a list of sort_refs, of the same length as the list of arguments. I'm unsure what this corresponds to *) ( ctx, Datatype.mk_constructor_s ctx.ctx_z3 name (Symbol.mk_string ctx.ctx_z3 name) (* We need a name for the argument of the constructor, we arbitrary pick the name of the constructor to which we append the special character "!" and the integer 0 *) [Symbol.mk_string ctx.ctx_z3 (name ^ "!0")] (* The type of the argument, translated to a Z3 sort *) [Some arg_z3_ty] [Sort.get_id arg_z3_ty] ) in match EnumMap.find_opt enum ctx.ctx_z3datatypes with | Some e -> ctx, e | None -> let ctrs = EnumMap.find enum ctx.ctx_decl.ctx_enums in let ctx, z3_ctrs = List.fold_left_map create_constructor ctx ctrs in let z3_enum = Datatype.mk_sort_s ctx.ctx_z3 (Marked.unmark (EnumName.get_info enum)) z3_ctrs in add_z3enum enum z3_enum ctx, z3_enum (** [find_or_create_struct] attemps to retrieve the Z3 sort corresponding to the struct [s]. If no such sort exists yet, we construct it as a datatype with one constructor taking all the fields as arguments, and add it to the context *) and find_or_create_struct (ctx : context) (s : StructName.t) : context * Sort.sort = match StructMap.find_opt s ctx.ctx_z3structs with | Some s -> ctx, s | None -> let s_name = Marked.unmark (StructName.get_info s) in let fields = StructMap.find s ctx.ctx_decl.ctx_structs in let z3_fieldnames = List.map (fun f -> Marked.unmark (StructFieldName.get_info (fst f)) |> Symbol.mk_string ctx.ctx_z3) fields in let ctx, z3_fieldtypes = List.fold_left_map (fun ctx f -> Marked.unmark (snd f) |> translate_typ ctx) ctx fields in let z3_sortrefs = List.map Sort.get_id z3_fieldtypes in let mk_struct_s = "mk!" ^ s_name in let z3_mk_struct = Datatype.mk_constructor_s ctx.ctx_z3 mk_struct_s (Symbol.mk_string ctx.ctx_z3 mk_struct_s) z3_fieldnames (List.map (fun x -> Some x) z3_fieldtypes) z3_sortrefs in let z3_struct = Datatype.mk_sort_s ctx.ctx_z3 s_name [z3_mk_struct] in add_z3struct s z3_struct ctx, z3_struct (** [translate_lit] returns the Z3 expression as a literal corresponding to [lit] **) let translate_lit (ctx : context) (l : lit) : Expr.expr = match l with | LBool b -> if b then Boolean.mk_true ctx.ctx_z3 else Boolean.mk_false ctx.ctx_z3 | LEmptyError -> failwith "[Z3 encoding] LEmptyError literals not supported" | LInt n -> Arithmetic.Integer.mk_numeral_i ctx.ctx_z3 (Runtime.integer_to_int n) | LRat r -> Arithmetic.Real.mk_numeral_s ctx.ctx_z3 (string_of_float (Runtime.decimal_to_float r)) | LMoney m -> let z3_m = Runtime.integer_to_int (Runtime.money_to_cents m) in Arithmetic.Integer.mk_numeral_i ctx.ctx_z3 z3_m | LUnit -> snd ctx.ctx_z3unit (* Encoding a date as an integer corresponding to the number of days since Jan 1, 1900 *) | LDate d -> Arithmetic.Integer.mk_numeral_i ctx.ctx_z3 (date_to_int d) | LDuration d -> let y, m, d = Runtime.duration_to_years_months_days d in if y <> 0 || m <> 0 then failwith "[Z3 encoding]: Duration literals containing years or months not \ supported"; Arithmetic.Integer.mk_numeral_i ctx.ctx_z3 d (** [find_or_create_funcdecl] attempts to retrieve the Z3 function declaration corresponding to the variable [v]. If no such function declaration exists yet, we construct it and add it to the context, thus requiring to return a new context *) let find_or_create_funcdecl (ctx : context) (v : Var.t) : context * FuncDecl.func_decl = match VarMap.find_opt v ctx.ctx_funcdecl with | Some fd -> ctx, fd | None -> ( (* Retrieves the Catala type of the function [v] *) let f_ty = VarMap.find v ctx.ctx_var in match Marked.unmark f_ty with | TArrow (t1, t2) -> let ctx, z3_t1 = translate_typ ctx (Marked.unmark t1) in let ctx, z3_t2 = translate_typ ctx (Marked.unmark t2) in let name = unique_name (Var.get v) in let fd = FuncDecl.mk_func_decl_s ctx.ctx_z3 name [z3_t1] z3_t2 in let ctx = add_funcdecl v fd ctx in let ctx = add_z3var name v ctx in ctx, fd | TAny -> failwith "[Z3 Encoding] A function being applied has type TAny, the type was \ not fully inferred" | _ -> failwith "[Z3 Encoding] Ill-formed VC, a function application does not have a \ function type") (** [translate_op] returns the Z3 expression corresponding to the application of [op] to the arguments [args] **) let rec translate_op (ctx : context) (op : operator) (args : 'm marked_expr list) : context * Expr.expr = match op with | Ternop _top -> let _e1, _e2, _e3 = match args with | [e1; e2; e3] -> e1, e2, e3 | _ -> failwith (Format.asprintf "[Z3 encoding] Ill-formed ternary operator application: %a" (Print.format_expr ctx.ctx_decl) ( EApp ( (EOp op, Untyped { pos = Pos.no_pos }), List.map untype_expr args ), Untyped { pos = Pos.no_pos } )) in failwith "[Z3 encoding] ternary operator application not supported" | Binop bop -> ( (* Special case for GetYear comparisons *) match bop, args with | Lt KInt, [(EApp ((EOp (Unop GetYear), _), [e1]), _); (ELit (LInt n), _)] -> let n = Runtime.integer_to_int n in let ctx, e1 = translate_expr ctx e1 in let e2 = Arithmetic.Integer.mk_numeral_i ctx.ctx_z3 (date_to_int (date_of_year n)) in (* e2 corresponds to the first day of the year n. GetYear e1 < e2 can thus be directly translated as < in the Z3 encoding using the number of days *) ctx, Arithmetic.mk_lt ctx.ctx_z3 e1 e2 | Lte KInt, [(EApp ((EOp (Unop GetYear), _), [e1]), _); (ELit (LInt n), _)] -> let n = Runtime.integer_to_int n in let ctx, e1 = translate_expr ctx e1 in let nb_days = if CalendarLib.Date.is_leap_year n then 365 else 364 in (* We want that the year corresponding to e1 is smaller or equal to n. We encode this as the day corresponding to e1 is smaller or equal than the last day of the year [n], which is Jan 1st + 365 days if [n] is a leap year, Jan 1st + 364 else *) let e2 = Arithmetic.Integer.mk_numeral_i ctx.ctx_z3 (date_to_int (date_of_year n) + nb_days) in ctx, Arithmetic.mk_le ctx.ctx_z3 e1 e2 | Gt KInt, [(EApp ((EOp (Unop GetYear), _), [e1]), _); (ELit (LInt n), _)] -> let n = Runtime.integer_to_int n in let ctx, e1 = translate_expr ctx e1 in let nb_days = if CalendarLib.Date.is_leap_year n then 365 else 364 in (* We want that the year corresponding to e1 is greater to n. We encode this as the day corresponding to e1 is greater than the last day of the year [n], which is Jan 1st + 365 days if [n] is a leap year, Jan 1st + 364 else *) let e2 = Arithmetic.Integer.mk_numeral_i ctx.ctx_z3 (date_to_int (date_of_year n) + nb_days) in ctx, Arithmetic.mk_gt ctx.ctx_z3 e1 e2 | Gte KInt, [(EApp ((EOp (Unop GetYear), _), [e1]), _); (ELit (LInt n), _)] -> let n = Runtime.integer_to_int n in let ctx, e1 = translate_expr ctx e1 in let e2 = Arithmetic.Integer.mk_numeral_i ctx.ctx_z3 (date_to_int (date_of_year n)) in (* e2 corresponds to the first day of the year n. GetYear e1 >= e2 can thus be directly translated as >= in the Z3 encoding using the number of days *) ctx, Arithmetic.mk_ge ctx.ctx_z3 e1 e2 | Eq, [(EApp ((EOp (Unop GetYear), _), [e1]), _); (ELit (LInt n), _)] -> let n = Runtime.integer_to_int n in let ctx, e1 = translate_expr ctx e1 in let min_date = Arithmetic.Integer.mk_numeral_i ctx.ctx_z3 (date_to_int (date_of_year n)) in let max_date = Arithmetic.Integer.mk_numeral_i ctx.ctx_z3 (date_to_int (date_of_year (n + 1))) in ( ctx, Boolean.mk_and ctx.ctx_z3 [ Arithmetic.mk_ge ctx.ctx_z3 e1 min_date; Arithmetic.mk_lt ctx.ctx_z3 e1 max_date; ] ) | _ -> ( let ctx, e1, e2 = match args with | [e1; e2] -> let ctx, e1 = translate_expr ctx e1 in let ctx, e2 = translate_expr ctx e2 in ctx, e1, e2 | _ -> failwith (Format.asprintf "[Z3 encoding] Ill-formed binary operator application: %a" (Print.format_expr ctx.ctx_decl) ( EApp ( (EOp op, Untyped { pos = Pos.no_pos }), List.map untype_expr args ), Untyped { pos = Pos.no_pos } )) in match bop with | And -> ctx, Boolean.mk_and ctx.ctx_z3 [e1; e2] | Or -> ctx, Boolean.mk_or ctx.ctx_z3 [e1; e2] | Xor -> ctx, Boolean.mk_xor ctx.ctx_z3 e1 e2 | Add KInt | Add KRat | Add KMoney | Add KDate | Add KDuration -> ctx, Arithmetic.mk_add ctx.ctx_z3 [e1; e2] | Sub KInt | Sub KRat | Sub KMoney | Sub KDate | Sub KDuration -> ctx, Arithmetic.mk_sub ctx.ctx_z3 [e1; e2] | Mult KInt | Mult KRat | Mult KMoney | Mult KDate | Mult KDuration -> ctx, Arithmetic.mk_mul ctx.ctx_z3 [e1; e2] | Div KInt | Div KRat | Div KMoney -> ctx, Arithmetic.mk_div ctx.ctx_z3 e1 e2 | Div _ -> failwith "[Z3 encoding] application of non-integer binary operator Div not \ supported" | Lt KInt | Lt KRat | Lt KMoney | Lt KDate | Lt KDuration -> ctx, Arithmetic.mk_lt ctx.ctx_z3 e1 e2 | Lte KInt | Lte KRat | Lte KMoney | Lte KDate | Lte KDuration -> ctx, Arithmetic.mk_le ctx.ctx_z3 e1 e2 | Gt KInt | Gt KRat | Gt KMoney | Gt KDate | Gt KDuration -> ctx, Arithmetic.mk_gt ctx.ctx_z3 e1 e2 | Gte KInt | Gte KRat | Gte KMoney | Gte KDate | Gte KDuration -> ctx, Arithmetic.mk_ge ctx.ctx_z3 e1 e2 | Eq -> ctx, Boolean.mk_eq ctx.ctx_z3 e1 e2 | Neq -> ctx, Boolean.mk_not ctx.ctx_z3 (Boolean.mk_eq ctx.ctx_z3 e1 e2) | Map -> failwith "[Z3 encoding] application of binary operator Map not supported" | Concat -> failwith "[Z3 encoding] application of binary operator Concat not supported" | Filter -> failwith "[Z3 encoding] application of binary operator Filter not supported")) | Unop uop -> ( let ctx, e1 = match args with | [e1] -> translate_expr ctx e1 | _ -> failwith (Format.asprintf "[Z3 encoding] Ill-formed unary operator application: %a" (Print.format_expr ctx.ctx_decl) ( EApp ( (EOp op, Untyped { pos = Pos.no_pos }), List.map untype_expr args ), Untyped { pos = Pos.no_pos } )) in match uop with | Not -> ctx, Boolean.mk_not ctx.ctx_z3 e1 | Minus _ -> failwith "[Z3 encoding] application of unary operator Minus not supported" (* Omitting the log from the VC *) | Log _ -> ctx, e1 | Length -> (* For now, an array is only its symbolic length. We simply return it *) ctx, e1 | IntToRat -> failwith "[Z3 encoding] application of unary operator IntToRat not supported" | GetDay -> failwith "[Z3 encoding] application of unary operator GetDay not supported" | GetMonth -> failwith "[Z3 encoding] application of unary operator GetMonth not supported" | GetYear -> failwith "[Z3 encoding] GetYear operator only supported in comparisons with \ literal" | RoundDecimal -> failwith "[Z3 encoding] RoundDecimal operator not implemented yet" | RoundMoney -> failwith "[Z3 encoding] RoundMoney operator not implemented yet") (** [translate_expr] translate the expression [vc] to its corresponding Z3 expression **) and translate_expr (ctx : context) (vc : 'm marked_expr) : context * Expr.expr = let translate_match_arm (head : Expr.expr) (ctx : context) (e : 'm marked_expr * FuncDecl.func_decl list) : context * Expr.expr = let e, accessors = e in match Marked.unmark e with | EAbs (e, _) -> (* Create a fresh Catala variable to substitue and obtain the body *) let fresh_v = new_var "arm!tmp" in let fresh_e = EVar fresh_v in (* Invariant: Catala enums always have exactly one argument *) let accessor = List.hd accessors in let proj = Expr.mk_app ctx.ctx_z3 accessor [head] in (* The fresh variable should be substituted by a projection into the enum in the body, we add this to the context *) let ctx = add_z3matchsubst (Var.t fresh_v) proj ctx in let body = Bindlib.msubst e [| fresh_e |] in translate_expr ctx body (* Invariant: Catala match arms are always lambda*) | _ -> failwith "[Z3 encoding] : Arms branches inside VCs should be lambdas" in match Marked.unmark vc with | EVar v -> ( match VarMap.find_opt (Var.t v) ctx.ctx_z3matchsubsts with | None -> (* We are in the standard case, where this is a true Catala variable *) let t = VarMap.find (Var.t v) ctx.ctx_var in let name = unique_name v in let ctx = add_z3var name (Var.t v) ctx in let ctx, ty = translate_typ ctx (Marked.unmark t) in let z3_var = Expr.mk_const_s ctx.ctx_z3 name ty in let ctx = match Marked.unmark t with (* If we are creating a new array, we need to log that its length is greater than 0 *) | TArray _ -> add_z3constraint (Arithmetic.mk_ge ctx.ctx_z3 z3_var (Arithmetic.Integer.mk_numeral_i ctx.ctx_z3 0)) ctx | _ -> ctx in ctx, z3_var | Some e -> (* This variable is a temporary variable generated during VC translation of a match. It actually corresponds to applying an accessor to an enum, the corresponding Z3 expression was previously stored in the context *) ctx, e) | ETuple _ -> failwith "[Z3 encoding] ETuple unsupported" | ETupleAccess (s, idx, oname, _tys) -> let name = match oname with | None -> failwith "[Z3 encoding]: ETupleAccess of unnamed struct unsupported" | Some n -> n in let ctx, z3_struct = find_or_create_struct ctx name in (* This datatype should have only one constructor, corresponding to mk_struct. The accessors of this constructor correspond to the field accesses *) let accessors = List.hd (Datatype.get_accessors z3_struct) in let accessor = List.nth accessors idx in let ctx, s = translate_expr ctx s in ctx, Expr.mk_app ctx.ctx_z3 accessor [s] | EInj (e, idx, en, _tys) -> (* This node corresponds to creating a value for the enumeration [en], by calling the [idx]-th constructor of enum [en], with argument [e] *) let ctx, z3_enum = find_or_create_enum ctx en in let ctx, z3_arg = translate_expr ctx e in let ctrs = Datatype.get_constructors z3_enum in (* This should always succeed if the expression is well-typed in dcalc *) let ctr = List.nth ctrs idx in ctx, Expr.mk_app ctx.ctx_z3 ctr [z3_arg] | EMatch (arg, arms, enum) -> let ctx, z3_enum = find_or_create_enum ctx enum in let ctx, z3_arg = translate_expr ctx arg in let _ctx, z3_arms = List.fold_left_map (translate_match_arm z3_arg) ctx (List.combine arms (Datatype.get_accessors z3_enum)) in let z3_arms = List.map2 (fun r arm -> (* Encodes A? arg ==> body *) let is_r = Expr.mk_app ctx.ctx_z3 r [z3_arg] in Boolean.mk_implies ctx.ctx_z3 is_r arm) (Datatype.get_recognizers z3_enum) z3_arms in ctx, Boolean.mk_and ctx.ctx_z3 z3_arms | EArray _ -> failwith "[Z3 encoding] EArray unsupported" | ELit l -> ctx, translate_lit ctx l | EAbs _ -> failwith "[Z3 encoding] EAbs unsupported" | EApp (head, args) -> ( match Marked.unmark head with | EOp op -> translate_op ctx op args | EVar v -> let ctx, fd = find_or_create_funcdecl ctx (Var.t v) in (* Fold_right to preserve the order of the arguments: The head argument is appended at the head *) let ctx, z3_args = List.fold_right (fun arg (ctx, acc) -> let ctx, z3_arg = translate_expr ctx arg in ctx, z3_arg :: acc) args (ctx, []) in ctx, Expr.mk_app ctx.ctx_z3 fd z3_args | _ -> failwith "[Z3 encoding] EApp node: Catala function calls should only include \ operators or function names") | EAssert _ -> failwith "[Z3 encoding] EAssert unsupported" | EOp _ -> failwith "[Z3 encoding] EOp unsupported" | EDefault _ -> failwith "[Z3 encoding] EDefault unsupported" | EIfThenElse (e_if, e_then, e_else) -> (* Encode this as (e_if ==> e_then) /\ (not e_if ==> e_else) *) let ctx, z3_if = translate_expr ctx e_if in let ctx, z3_then = translate_expr ctx e_then in let ctx, z3_else = translate_expr ctx e_else in ( ctx, Boolean.mk_and ctx.ctx_z3 [ Boolean.mk_implies ctx.ctx_z3 z3_if z3_then; Boolean.mk_implies ctx.ctx_z3 (Boolean.mk_not ctx.ctx_z3 z3_if) z3_else; ] ) | ErrorOnEmpty _ -> failwith "[Z3 encoding] ErrorOnEmpty unsupported" (** [create_z3unit] creates a Z3 sort and expression corresponding to the unit type and value respectively. Concretely, we represent unit as a tuple with 0 elements **) let create_z3unit (ctx : Z3.context) : Z3.context * (Sort.sort * Expr.expr) = let unit_sort = Tuple.mk_sort ctx (Symbol.mk_string ctx "unit") [] [] in let mk_unit = Tuple.get_mk_decl unit_sort in let unit_val = Expr.mk_app ctx mk_unit [] in ctx, (unit_sort, unit_val) module Backend = struct type backend_context = context type vc_encoding = Z3.Expr.expr let print_encoding (vc : vc_encoding) : string = Expr.to_string vc type model = Z3.Model.model type solver_result = ProvenTrue | ProvenFalse of model option | Unknown let solve_vc_encoding (ctx : backend_context) (encoding : vc_encoding) : solver_result = let solver = Z3.Solver.mk_solver ctx.ctx_z3 None in (* We take the negation of the query to check for possible counterexamples *) let query = Boolean.mk_not ctx.ctx_z3 encoding in (* Add all the hypotheses stored in the context *) let query_and_hyps = query :: ctx.ctx_z3constraints in Z3.Solver.add solver query_and_hyps; match Z3.Solver.check solver [] with | UNSATISFIABLE -> ProvenTrue | SATISFIABLE -> ProvenFalse (Z3.Solver.get_model solver) | UNKNOWN -> Unknown let print_model (ctx : backend_context) (m : model) : string = print_model ctx m let is_model_empty (m : model) : bool = List.length (Z3.Model.get_decls m) = 0 let translate_expr (ctx : backend_context) (e : 'm marked_expr) = translate_expr ctx e let init_backend () = Cli.debug_print "Running Z3 version %s" Version.to_string let make_context (decl_ctx : decl_ctx) (free_vars_typ : typ Marked.pos VarMap.t) : backend_context = let cfg = (if !Cli.disable_counterexamples then [] else ["model", "true"]) @ ["proof", "false"] in let z3_ctx = mk_context cfg in let z3_ctx, z3unit = create_z3unit z3_ctx in { ctx_z3 = z3_ctx; ctx_decl = decl_ctx; ctx_var = free_vars_typ; ctx_funcdecl = VarMap.empty; ctx_z3vars = StringMap.empty; ctx_z3datatypes = EnumMap.empty; ctx_z3matchsubsts = VarMap.empty; ctx_z3structs = StructMap.empty; ctx_z3unit = z3unit; ctx_z3constraints = []; } end module Io = Io.MakeBackendIO (Backend)