Path: Module for Substitutions within S-expressions
Types
type el = 
|Pos of int
Pos n denotes nth element in a tuple
|Match of string * int
Match (tag, n) denotes nth argument of sum matching tag
|Rec of string
Rec name denotes the record field having name
Type of substitution elements
type t = el list
Type of substitution paths
High-level functions
val parse : string -> t
parse str Raises Failure if the path is syntactically invalid.
Returns a substitution path represented by string str.

Syntax:

"." -> separates path elements; must be present at start of string.

"[4]" -> specifies the 4th element in a tuple.

"some_tag[4]" -> tries to match some_tag, then denotes its 4th argument.

"name" -> denotes record field having name

Example from test code:

".t.x.B1" -> choose record field with name t, then subfield x. Match this value against B, and denote its first argument.

val get : ?path:t -> ?str:string -> Sexp.t -> Sexp.t
get ?path ?str sexp if path is provided, use it as path. Otherwise, if str is provided, parse it as a path. If neither is provided, assume an empty path. Raises Failure if path is syntactically invalid or if the path structure clashes with the structure of the data.
Returns the sub-expression from S-expression sexp denoted by the path.
val replace : ?path:t -> ?str:string -> Sexp.t -> subst:Sexp.t -> Sexp.t
replace ?path ?str sexp ~subst like get, but does not extract a sub-expression but substitutes it with subst. Raises Failure if path is syntactically invalid or if the path structure clashes with the structure of the data.
Returns resulting S-expression.
val replace_no_path : str:string -> Sexp.t -> subst:Sexp.t -> Sexp.t
replace_no_path ~str sexp ~subst like replace, but does not take optional arguments. str must be specified. Raises Failure if path is syntactically invalid or if the path structure clashes with the structure of the data.
val subst_path : Sexp.t -> t -> (Sexp.t -> Sexp.t) * Sexp.t
subst_path sexp path Raises Failure if path is syntactically invalid or if the path structure clashes with the structure of the data.
Returns the tuple (subst, sub), where subst is a function that returns an S-expression in which the subexpression denoted by path in sexp has been substituted by its argument. sub is the denoted subexpression. Note that subst sub = sexp.
Low-level functions
val extract_pos : int -> Sexp.t -> (Sexp.t option -> Sexp.t) * Sexp.t
extract_pos n sexp Raises Failure if the position cannot be resolved within the given S-expression.
Returns the tuple (subst, sub), where subst is a function that returns an S-expression in which the subexpression denoted at position n in sexp, which must be a list, has been substituted by value if the optional argument is Some value, or removes the denoted subexpression if the optional argument is None. sub is the denoted subexpression. Note that subst (Some sub) = sexp.
val extract_match : string -> int -> Sexp.t -> (Sexp.t option -> Sexp.t) * Sexp.t
extract_match tag n sexp Raises Failure if the S-expression does not represent a sum tag.
Returns the tuple (subst, sub), where subst is a function that returns an S-expression in which the subexpression denoted by matching tag and taking its nth argument in sexp has been substituted by value if the argument is Some value, or removes the denoted subexpression if the optional argument is None. sub is the denoted subexpression. Note that subst (Some sub) = sexp.
val extract_rec : string -> Sexp.t -> (Sexp.t -> Sexp.t) * Sexp.t
extract_rec name sexp Raises Failure if the S-expression does not represent a record.
Returns the tuple (subst, sub), where subst is a function that returns an S-expression in which the subexpression denoted by matching field name name in sexp has been substituted by its argument. sub is the denoted subexpression. Note that subst (Some sub) = sexp.