(* This module transforms [Front.grammar], an abstract syntax tree for
the grammar, into an internal representation of the grammar that is
more usable. *)
(* ------------------------------------------------------------------------ *)
(* Nonterminals. *)
module Nonterminal : sig
(* The type of nonterminals. *)
type t
(* The number of nonterminals. This includes the extra nonterminals
that are internally generated for the grammar's entry points. *)
val n: int
(* [lookup] maps an identifier to a nonterminal, or raises [Not_found]. *)
val lookup : string -> t
(* Nonterminals can be converted to integers. This feature is
exploited in the table-based back-end. *)
val n2i: t -> int
(* This produces a string representation of a nonterminal. It should
in principle never be applied to one of the internally generated
nonterminals, as we do not wish users to become aware of the
existence of these extra nonterminals. However, we do sometimes
violate this rule when it is difficult to do otherwise.
The Boolean parameter tells whether the string representation
should be normalized, that is, whether parentheses and commas
should be eliminated. This is necessary if the string is intended
for use as a valid nonterminal name or as a valid Objective Caml
identifier. *)
val print: bool -> t -> string
(* This is the Objective Caml type associated with a nonterminal
symbol. It is known only if a %type declaration was provided.
This function is not applicable to the internally generated
nonterminals. *)
val ocamltype: t -> Stretch.ocamltype option
(* A start symbol always has a type. This allows us to define
a simplified version of [ocamltype] for start symbols. *)
val ocamltype_of_start_symbol: t -> Stretch.ocamltype
(* Iteration over nonterminals. The order in which elements are
examined, and the order of [map]'s output list, correspond to the
numeric indices produced by [n2i] above. *)
val iter: (t -> unit) -> unit
val fold: (t -> 'a -> 'a) -> 'a -> 'a
val map: (t -> 'a) -> 'a list
(* Iteration over all nonterminals, except the start nonterminals. *)
val iterx: (t -> unit) -> unit
val foldx: (t -> 'a -> 'a) -> 'a -> 'a
(* Tabulation of a function over nonterminals. *)
val tabulate: (t -> 'a) -> (t -> 'a)
(* [positions nt] is a list of the positions associated with the
definition of [nt]. There can be more than one position because
definitions can be split over multiple files. *)
val positions: t -> Positions.t list
(* This tells whether a non-terminal symbol is one of the start
symbols. *)
val is_start: t -> bool
end
(* ------------------------------------------------------------------------ *)
(* Terminals. *)
module Terminal : sig
(* The type of terminals. *)
type t
(* The number of terminals. This includes the two pseudo-tokens
[#] and [error]. *)
val n: int
(* Comparison. *)
val equal: t -> t -> bool
(* [lookup] maps an identifier to a terminal, or raises [Not_found]. *)
val lookup : string -> t
(* Terminals can be converted to integers. This feature is exploited
in the table-based back-end. *)
val t2i: t -> int
(* This produces a string representation of a terminal. *)
val print: t -> string
(* This is the Objective Caml type associated with a terminal
symbol. It is known only if the %token declaration was
accompanied with a type. *)
val ocamltype: t -> Stretch.ocamltype option
(* These are the two pseudo-tokens [#] and [error]. The former is
used to denote the end of the token stream. The latter is
accessible to the user and is used for handling errors. *)
val sharp: t
val error: t
(* This is the programmer-defined [EOF] token, if there is one. It
is recognized based solely on its name, which is fragile, but
this behavior is documented. This token is assumed to represent
[ocamllex]'s [eof] pattern. It is used only by the reference
interpreter, and in a rather non-essential way. *)
val eof: t option
(* This returns [true] if and only if the token at hand is one of
[#] or [error]. *)
val pseudo: t -> bool
(* Iteration over terminals. The order in which elements are
examined, and the order of [map]'s output list, correspond to the
numeric indices produced by [t2i] above. [mapx] offers iteration
over all terminals except [#]. *)
val iter: (t -> unit) -> unit
val fold: (t -> 'a -> 'a) -> 'a -> 'a
val map: (t -> 'a) -> 'a list
val mapx: (t -> 'a) -> 'a list
end
(* ------------------------------------------------------------------------ *)
(* Sets and maps over terminals. *)
module TerminalSet : sig
(* All of the operations documented in [GSet] are available. *)
include GSet.S with type element = Terminal.t
(* This offers a string representation of a set of terminals. The
symbols are simply listed one after the other and separated with
spaces. *)
val print: t -> string
(* This is the set of all terminal symbols except the pseudo-tokens
[#] and [error]. *)
val universe: t
end
(* All of the operations documented in [GMap] are available. *)
module TerminalMap : GMap.S with type key = Terminal.t
(* ------------------------------------------------------------------------ *)
(* Symbols. *)
module Symbol : sig
(* A symbol is either a nonterminal or a terminal. *)
type t =
| N of Nonterminal.t
| T of Terminal.t
(* Comparison. *)
val equal: t -> t -> bool
val lequal: t list -> t list -> bool
(* These produce a string representation of a symbol, of a list of
symbols, or of an array of symbols. The symbols are simply listed
one after the other and separated with spaces. [printao] prints
an array of symbols, starting at a particular offset. [printaod]
is analogous, but can also print a single dot at a particular
position between two symbols. *)
val print: t -> string
val printl: t list -> string
val printa: t array -> string
val printao: int -> t array -> string
val printaod: int -> int -> t array -> string
end
(* ------------------------------------------------------------------------ *)
(* Sets and maps over symbols. *)
(* All of the operations documented in [Set] are available. *)
module SymbolSet : Set.S with type elt = Symbol.t
module SymbolMap : sig
(* All of the operations documented in [Map] are available. *)
include Map.S with type key = Symbol.t
val domain: 'a t -> key list
(* This returns [true] if and only if all of the symbols in
the domain of the map at hand are nonterminals. *)
val purelynonterminal: 'a t -> bool
end
(* ------------------------------------------------------------------------ *)
(* Productions. *)
module Production : sig
(* This is the type of productions. This includes user-defined
productions as well as the internally generated productions
associated with the start symbols. *)
type index
(* Productions can be converted to integers and back. This is unsafe
and should be avoided as much as possible. This feature is
exploited, for efficiency, in the encoding of items. *)
val p2i: index -> int
val i2p: int -> index
(* The number of productions. *)
val n: int
(* These map a production index to the production's definition, that
is, a nonterminal (the left-hand side) and an array of symbols
(the right-hand side). *)
val def: index -> Nonterminal.t * Symbol.t array
val nt: index -> Nonterminal.t
val rhs: index -> Symbol.t array
val length: index -> int
(* This maps a production index to an array of the identifiers that
should be used for naming the semantic values of the symbols in
the right-hand side. *)
val identifiers: index -> Syntax.identifier array
(* This maps a production index to the production's semantic action.
This function is not applicable to a start production. *)
val action: index -> Syntax.action
(* [positions prod] is a list of the positions associated with
production [prod]. This is usually a singleton list, but there
can be more than one position for start productions when the
definition of the corresponding start symbol is split over
multiple files. *)
val positions: index -> Positions.t list
(* Iteration over all productions. The order in which elements
are examined, and the order of [map]'s output list, correspond
to the numeric indices produced by [p2i] above. *)
val iter: (index -> unit) -> unit
val fold: (index -> 'a -> 'a) -> 'a -> 'a
val map: (index -> 'a) -> 'a list
val amap: (index -> 'a) -> 'a array
(* Iteration over all productions, except the start productions. *)
val iterx: (index -> unit) -> unit
val foldx: (index -> 'a -> 'a) -> 'a -> 'a
val mapx: (index -> 'a) -> 'a list
(* This maps a (user) non-terminal start symbol to the corresponding
start production. *)
val startsymbol2startprod: Nonterminal.t -> index
(* Iteration over the productions associated with a specific
nonterminal. *)
val iternt: Nonterminal.t -> (index -> unit) -> unit
val foldnt: Nonterminal.t -> 'a -> (index -> 'a -> 'a) -> 'a
(* This allows determining whether a production is a start
production. If it is a start production, the start symbol that it
is associated with is returned. If it is a regular production,
nothing is returned. *)
val classify: index -> Nonterminal.t option
(* [is_start] is easier to use than [classify] when the start symbol
is not needed. *)
val is_start: index -> bool
(* The integer [start] is published so as to allow the table back-end
to produce code for [is_start]. It should not be used otherwise. *)
val start: int
(* This produces a string representation of a production. It should
never be applied to a start production, as we do not wish users
to become aware of the existence of these extra productions. *)
val print: index -> string
(* Tabulation of a Boolean function over productions. [tabulateb f]
returns a tabulated version of [f] as well as the number of
productions where [f] is true. *)
val tabulate: (index -> 'a) -> (index -> 'a)
val tabulateb: (index -> bool) -> (index -> bool) * int
end
(* ------------------------------------------------------------------------ *)
(* Maps over productions. *)
module ProductionMap : sig
include GMap.S with type key = Production.index
(* Iteration over the start productions only. *)
val start: (Production.index -> 'a) -> 'a t
end
(* ------------------------------------------------------------------------ *)
(* Analysis of the grammar. *)
module Analysis : sig
(* [nullable nt] is the NULLABLE flag of the non-terminal symbol [nt].
That is, it is true if and only if this symbol produces the empty
word [epsilon]. *)
val nullable: Nonterminal.t -> bool
(* [first nt] is the FIRST set of the non-terminal symbol [nt]. *)
val first: Nonterminal.t -> TerminalSet.t
(* [nullable_first_prod prod i] considers the suffix of the the production
[prod] defined by offset [i]. It returns its NULLABLE flag as well
as its FIRST set. The offset [i] must be contained between [0] and
[n], inclusive, where [n] is the length of production [prod]. *)
val nullable_first_prod: Production.index -> int -> bool * TerminalSet.t
(* [explain_first_rhs tok rhs i] explains why the token [tok] appears
in the FIRST set for the string of symbols found at offset [i] in
the array [rhs]. *)
val explain_first_rhs: Terminal.t -> Symbol.t array -> int -> string
(* [follow nt] is the FOLLOW set of the non-terminal symbol [nt], that
is, the set of terminal symbols that could follow an expansion of
[nt] in a valid sentence. *)
val follow: Nonterminal.t -> TerminalSet.t
end
(* ------------------------------------------------------------------------ *)
(* Conflict resolution via precedences. *)
module Precedence : sig
(* Shift/reduce conflicts require making a choice between shifting a
token and reducing a production. How these choices are made is of
no concern to the back-end, but here is a rough explanation.
Shifting is preferred when the token has higher precedence than
the production, or they have same precedence and the token is
right-associative.
Reducing is preferred when the token has lower precedence than
the production, or they have same precedence and the token is
left-associative.
Neither is allowed when the token and the production have same
precedence and the token is non-associative.
No preference is explicitly specified when the token or the
production has undefined precedence. In that case, the default
choice is to prefer shifting, but a conflict will be reported. *)
type choice =
| ChooseShift
| ChooseReduce
| ChooseNeither
| DontKnow
val shift_reduce: Terminal.t -> Production.index -> choice
(* Reduce/reduce conflicts require making a choice between reducing
two distinct productions. This is done by exploiting a partial
order on productions.
For compatibility with ocamlyacc, this order should be total and
should correspond to textual order when the two productions
originate in the same source file. When they originate in
different source files, the two productions should be
incomparable. *)
val reduce_reduce: Production.index -> Production.index -> Production.index option
end
(* ------------------------------------------------------------------------ *)
(* Diagnostics. *)
(* This function prints diagnostics about precedence declarations that
are never consulted. It is called after the automaton is
constructed. *)
val diagnostics: unit -> unit