elpi.trace.ppx provides the following syntax extensions:

type t = a : T; b : S [@trace]

let rec f x (w@trace) = %trace "f" (fun fmt -> .. x ..) begin match x with | K1 -> ... | K2 x -> [%tcall f x] | K2(x,y) -> let z = f x in [%spy "z" ~rid ~gid ~cond (fun fmt z -> .. z ..) z]; [%spyl "z" ~rid ~gid ~cond (fun fmt z -> .. z ..) zs]; [%log "K2" "whatever" 37]; let x[@trace] = ... in e let w = { a; b = b[@trace ] } in match w with | { a; b = b [@trace] } -> z + f y (b[@trace]) end

If --cookie "elpi_trace=\"true\"" is not passed to the ppx rewriter:

  • %trace "foo" pp code ---> code
  • %tcall f x ---> f x
  • %spy ... %spyl ... and %log ... ---> ()
  • f x (y@trace) z ---> f x z
  • let x@trace = .. in e ---> e
  • type x = a : T; b : T [@trace] ---> type x = a : T
  • a; b = b [@trace] ---> a (in both patterns and expressions)
  • T -> (S@trace) -> U ---> T -> U

In records, the shorcut "x" to mean "x = x" does not work, you have to use the longer form.

val err : loc:Ppxlib.Location.t -> string -> 'a
val enabled : bool ref
val has_iftrace_attribute : Ppxlib.attributes -> bool
val has_iftrace : Ppxlib.core_type -> bool
val map_trace : Ppxlib.Ast_traverse.map
val is_string_literal : Ppxlib.expression -> bool
val is_gid : Ppxlib.arg_label -> bool
val is_rid : Ppxlib.arg_label -> bool
val is_cond : Ppxlib.arg_label -> bool
val pull : ('a -> bool) -> ('a * 'b) list -> 'b option * ('a * 'b) list
val err_spy : loc:Ppxlib.Location.t -> unit -> 'a
val spyl_expand_function : loc:Ppxlib.location -> path:'a -> Ppxlib.expression -> Ppxlib_ast.Ast.expression
val spyl_extension : Ppxlib.Extension.t
val spy_expand_function : loc:Ppxlib.location -> path:'a -> Ppxlib.expression -> Ppxlib_ast.Ast.expression
val spy_extension : Ppxlib.Extension.t
val tcall_expand_function : loc:Ppxlib.location -> path:'a -> Ppxlib.expression -> Ppxlib_ast.Ast.expression
val tcall_extension : Ppxlib.Extension.t
val trace_expand_function : loc:Ppxlib.location -> path:'a -> Ppxlib.expression -> Ppxlib_ast.Ast.expression
val trace_extension : Ppxlib.Extension.t
val cur_pred_expand_function : loc:Ppxlib.location -> path:'a -> Ppxlib_ast.Ast.expression -> Ppxlib_ast.Ast.expression
val cur_pred_extension : Ppxlib.Extension.t
val cur_pred_rule : Ppxlib.Context_free.Rule.t
val log_expand_function : loc:Ppxlib.location -> path:'a -> Ppxlib_ast.Ast.expression -> Ppxlib_ast.Ast.expression
val log_extension : Ppxlib.Extension.t
val arg_trace : Ppxlib.Driver.Cookies.t -> unit