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+(** This module defines the AST which is to be extracted to generate code.
+    This AST is voluntarily as simple as possible, so that the extraction
+    can focus on pretty-printing and on the syntax specific to the different
+    provers.
+ *)
+
+type constant_value = Pure.constant_value
+
+type pattern =
+  | PatVar of string
+  | PatDummy
+  | PatEnum of string * pattern list
+      (** Enum: the constructor name (tuple if `None`) and the fields.
+          Note that we never use structures as patters: we access the fields one
+          by one.
+       *)
+  | PatTuple of pattern list
+
+(** We want to keep terms a little bit structured, for pretty printing.
+    See the `FieldProj` and the `Record` cases, for instance.
+ *)
+type term =
+  | Constant of constant_value
+  | Var of string
+  | FieldProj of term * term
+      (** `x.y`
+
+           Of course, we can always use projectors like `record_get_y x`:
+           this variant is for pretty-printing.
+           
+           Note that `FieldProj` are generated when translating `place` from
+           the "pure" AST.
+       *)
+  | App of term * term
+  | Let of bool * pattern * term * term
+  | If of term * term * term
+  | Switch of term * (pattern * term) list
+  | Ascribed of term * term  (** `x <: ty` *)
+  | Tuple of term list
+  | Record of (string * term) list
+      (** In case a record has named fields, we try to use them, to generate
+          code like: `{ x = 3; y = true; }`
+          Otherwise, we can use `App` (with the record constructor).
+       *)
+
+type fun_def = {
+  name : string;
+  inputs : pattern list;
+      (** We can match over the inputs, hence the use of [pattern]. In practice,
+          we use [PatVar] and [PatDummy].
+       *)
+  input_tys : term list;
+  output_ty : term;
+  body : term;
+}