Module Analysis.Unparse

Implementation of the "unparsing" functionality. The goal of this feature is to enable parsers to be used as printers by manually providing a Common.bindings object with a structure matching those returned by Parse.run_parse.

Fundamentally, unparsing relies on the placement of Common.parseable.Bind operators to disambiguate between Common.parseable.Or alternatives.

To make a parseable which is suitable for unparsing, you have two options when using Or operators:

• (1) Place the Or directly within a Bind, recording the result of the Or as a new binding. This is most suitable where the Or alternatives are simple literals. Binding complex expressions in this way makes it more difficult to construct the bindings needed by Unparse.unparse.
• (2) Use distinct Bind names within each Or alternative. The unparsing will choose the alternative which is most applicable given the available bindings. When using this, you should ensure that the binding names, together with the number of times they're bound, is sufficient to disambiguate alternatives. The unparse will fail if it cannot determine a unique best alternative.

Furthermore, a Common.parseable.Bind should not be nested within a Common.parseable.Bind with the same binding name. This will cause leftover bindings as the unparse will not visit the inner Bind. Repeating the same binding name in a manner which is not conceptually a repetition is discouraged.

Both approaches are demonstrated in this example:

# let spec_around_or = bind "Xd" (literals ["x1"; "x2"])
val spec_around_or : parseable =
  Bind {name = "Xd"; syntax = Or [Lit "x1"; Lit "x2"] }
# let spec_within_or = Or [bind "case1" (literals ["x1"]); bind "case2" (literals ["x2"])]
val spec_within_or : parseable =
  Or
   [Bind {name = "case1"; syntax = Lit "x1"};
    Bind {name = "case2"; syntax = Lit "x2"} ]

# let print_unparse p bs = show_parse_output @@ unparse_with_bindings p bs
val print_unparse : parseable -> Lang__.Common.bindings -> string = <fun>

# print_unparse spec_around_or @@ binding "Xd" (output_str "x1")
- : string = "tokens=[\"x1\"] bindings={ Xd=[] }"
# print_unparse spec_around_or @@ binding "Xd" (output_str "anything");
- : string = "tokens=[\"anything\"] bindings={ Xd=[] }"

# print_unparse spec_within_or @@ binding "case1" (output_str "x1");
- : string = "tokens=[\"x1\"] bindings={ case1=[] }"
# print_unparse spec_within_or @@ binding "case2" (output_str "anything");
- : string = "tokens=[\"anything\"] bindings={ case2=[] }"