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+open Core
+
+(* Binary operators *)
+type binary_op =
+  | Plus
+  | Minus
+  | Mult
+  | Div
+  | Gt
+  | Lt
+  | Lte
+  | Gte
+  | Eq
+  | Neq
+  | Or
+  | And
+  | Impl
+  | Merge
+  | Concat
+[@@deriving sexp_of]
+
+(* Unary operators *)
+type unary_op = Negate | Not [@@deriving sexp_of]
+
+(* The top-level expression type *)
+type expr =
+  | BinaryOp of binary_op * expr * expr
+  | UnaryOp of unary_op * expr
+  | Cond of expr * expr * expr
+  | With of expr * expr
+  | Assert of expr * expr
+  | Test of expr * expr list
+  | SetLet of binding list
+  | Let of binding list * expr
+  | Val of value
+  | Id of id
+  | Select of expr * expr list * expr option
+  | Apply of expr * expr
+  | Aquote of expr
+[@@deriving sexp_of]
+
+(* Possible values *)
+and value =
+  (* Str is a string start, followed by arbitrary number of antiquotations and
+     strings that separate them *)
+  | Str of string * (expr * string) list
+  (* IStr is an indented string, so it has the extra integer component which
+     indicates the indentation *)
+  | IStr of int * string * (expr * string) list
+  | Int of string
+  | Float of string
+  | Path of string
+  | SPath of string
+  | HPath of string
+  | Uri of string
+  | Lambda of pattern * expr
+  | List of expr list
+  | AttSet of recursivity * binding list
+[@@deriving sexp_of]
+
+(* Patterns in lambda definitions *)
+and pattern = Alias of id | ParamSet of id option * param_set
+[@@deriving sexp_of]
+
+and param_set = param list * match_kind [@@deriving sexp_of]
+and param = id * expr option [@@deriving sexp_of]
+and recursivity = Rec | Nonrec
+and match_kind = Exact | Loose
+
+(* Bindings in attribute sets and let expressions *)
+and binding =
+  (* The first expr should be attrpath, which is the same as in Select *)
+  | AttrPath of expr list * expr
+  | Inherit of expr option * expr list
+[@@deriving sexp_of]
+
+(* Identifiers *)
+and id = string
+
+(* Precedence levels of binary operators *)
+let prec_of_bop = function
+  | Concat -> 5
+  | Mult | Div -> 6
+  | Plus | Minus -> 7
+  | Merge -> 9
+  | Gt | Lt | Lte | Gte -> 10
+  | Eq | Neq -> 11
+  | And -> 12
+  | Or -> 13
+  | Impl -> 14
+
+type assoc = Left | Right
+
+let assoc_of_bop = function
+  | Mult | Div | Plus | Minus -> Some Left
+  | Concat | Merge | And | Or -> Some Right
+  | Gt | Lt | Lte | Gte | Eq | Neq | Impl -> None
+
+(* Precedence levels of unary operators *)
+let prec_of_uop = function Negate -> 3 | Not -> 8
+
+(* Precedence level of expressions
+   (assuming that the constituents have higher levels) *)
+let prec_of_expr = function
+  | Val (Lambda _) -> 15
+  | Val _ | Id _ | Aquote _ -> 0
+  | BinaryOp (op, _, _) -> prec_of_bop op
+  | UnaryOp (op, _) -> prec_of_uop op
+  | Cond _ | With _ | Assert _ | Let _ | SetLet _ -> 15
+  | Test _ -> 4
+  | Select _ -> 1
+  | Apply _ -> 2