IncrementalEngine.ml 7.68 KB
Newer Older
1 2 3 4 5 6 7 8 9 10
(* This signature describes the incremental LR engine. *)

(* In this mode, the user controls the lexer, and the parser suspends
   itself when it needs to read a new token. *)

module type INCREMENTAL_ENGINE = sig

  type token

  (* The type ['a result] represents an intermediate or final result of the
11 12 13 14 15 16 17 18 19 20 21
     parser. An intermediate result is a suspension: it records the parser's
     current state, and allows parsing to be resumed. The parameter ['a] is
     the type of the semantic value that will eventually be produced if the
     parser succeeds. *)

  (* [Accepted] and [Rejected] are final results. [Accepted] carries a
     semantic value. *)

  (* [InputNeeded] is an intermediate result. It means that the parser wishes
     to read one token before continuing. *)

22 23 24 25 26 27 28 29 30 31
  (* [AboutToReduce] is an intermediate result. It means that the parser is
     about to perform a reduction step. It does not need more input at this
     point. The parser suspends itself at this point only in order to give the
     user an opportunity to observe this reduction step. *)

  (* [HandlingError] is an intermediate result. It means that the parser has
     detected an error and is currently handling it, in several steps. It does
     not need more input at this point. The parser suspends itself at this
     point only in order to give the user an opportunity to handle this error
     in a different manner, if desired. *)
32

33
  type env
34

35 36
  type production

37 38 39 40
  type 'a result = private
    | InputNeeded of env
    | AboutToReduce of env * production
    | HandlingError of env
41 42 43 44
    | Accepted of 'a
    | Rejected

  (* [offer] allows the user to resume the parser after it has suspended
45 46 47
     itself with a result of the form [InputNeeded env]. [offer] expects the
     old result as well as a new token and produces a new result. It does not
     raise any exception. *)
48 49

  val offer:
50
    'a result ->
51 52 53
    token * Lexing.position * Lexing.position ->
    'a result

54 55 56 57
  (* [resume] allows the user to resume the parser after it has suspended
     itself with a result of the form [AboutToReduce (env, prod)] or
     [HandlingError env]. [resume] expects the old result and produces a new
     result. It does not raise any exception. *)
58

59 60
  val resume:
    'a result ->
61 62
    'a result

63 64 65 66 67 68 69 70 71 72 73 74 75 76 77
  (* The abstract type ['a lr1state] describes the non-initial states of the
     LR(1) automaton. The index ['a] represents the type of the semantic value
     associated with this state's incoming symbol. *)

  type 'a lr1state

  (* A stream is a list whose elements are produced on demand. *)

  type 'a stream =
      'a head Lazy.t

  and 'a head =
    | Nil
    | Cons of 'a * 'a stream

78 79 80 81 82 83 84 85
  (* The length of a stream. *)

  val length: 'a stream -> int

  (* Folding over a stream. *)

  val foldr: ('a -> 'b -> 'b) -> 'a stream -> 'b -> 'b

86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101
  (* An element is a pair of a non-initial state [s] and a semantic value [v]
     associated with the incoming symbol of this state. The idea is, the value
     [v] was pushed onto the stack just before the state [s] was entered. Thus,
     for some type ['a], the type [s] has type ['a lr1state] and the value [v]
     has type ['a]. In other words, the type [element] is an existential type. *)

  type element =
    | Element: 'a lr1state * 'a * Lexing.position * Lexing.position -> element

  (* The parser's stack is (or, more precisely, can be viewed as) a stream of
     elements. *)

  type stack =
    element stream

  (* The parser's stack, a stream of elements, can be examined. This stream is
POTTIER Francois's avatar
POTTIER Francois committed
102
     empty if the parser is in an initial state; otherwise, it is non-empty.
103 104
     The LR(1) automaton's current state is the one found in the top element
     of the stack. *)
105

106
  val stack: env -> stack
107

108
end
109

110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139
(* This signature is a fragment of the inspection API that is made available
   to the user when [--inspection] is used. This fragment contains type
   definitions for symbols. *)

module type SYMBOLS = sig

  (* The type ['a terminal] represents a terminal symbol. The type ['a
     nonterminal] represents a nonterminal symbol. In both cases, the index
     ['a] represents the type of the semantic values associated with this
     symbol. The concrete definitions of these types are generated. *)

  type 'a terminal
  type 'a nonterminal

  (* The type ['a symbol] represents a terminal or nonterminal symbol. It is
     the disjoint union of the types ['a terminal] and ['a nonterminal]. *)

  type 'a symbol =
    | T : 'a terminal -> 'a symbol
    | N : 'a nonterminal -> 'a symbol

  (* The type [xsymbol] is an existentially quantified version of the type
     ['a symbol]. This type is useful in situations where the index ['a]
     is not statically known. *)

  type xsymbol = 
    | X : 'a symbol -> xsymbol

end

140 141
(* This signature describes the inspection API that is made available to the
   user when [--inspection] is used. *)
142 143 144

module type INSPECTION = sig

145 146 147 148
  (* The types of symbols are described above. *)

  include SYMBOLS

149 150 151 152 153 154 155
  (* Ordering functions. *)

  val compare_terminals: _ terminal -> _ terminal -> int
  val compare_nonterminals: _ nonterminal -> _ nonterminal -> int
  val compare_symbols: xsymbol -> xsymbol -> int
  val compare_words: xsymbol list -> xsymbol list -> int

156 157
  (* The type ['a lr1state] is meant to be the same as in [INCREMENTAL_ENGINE]. *)

158
  type 'a lr1state
159

160 161 162 163
  (* The type [production] is meant to be the same as in [INCREMENTAL_ENGINE].
     It represents a production of the grammar. A production can be examined
     via the functions [lhs] and [rhs] below. *)

164 165
  type production

166 167 168 169
  (* An LR(0) item is a pair of a production [prod] and a valid index [i] into
     this production. That is, if the length of [rhs prod] is [n], then [i] is
     comprised between 0 and [n], inclusive. *)

170
  type item =
171 172 173 174 175 176 177 178
      production * int

  (* [incoming_symbol s] is the incoming symbol of the state [s], that is,
     the symbol that the parser must recognize before (has recognized when)
     it enters the state [s]. This function gives access to the semantic
     value [v] stored in a stack element [Element (s, v, _, _)]. Indeed,
     by case analysis on the symbol [incoming_symbol s], one discovers the
     type ['a] of the value [v]. *)
179

POTTIER Francois's avatar
POTTIER Francois committed
180
  val incoming_symbol: 'a lr1state -> 'a symbol
181

182 183 184
  (* [lhs prod] is the left-hand side of the production [prod]. This is
     always a non-terminal symbol. *)

185 186
  val lhs: production -> xsymbol

187 188 189
  (* [rhs prod] is the right-hand side of the production [prod]. This is
     a (possibly empty) sequence of (terminal or nonterminal) symbols. *)

190 191
  val rhs: production -> xsymbol list

192
  (* [items s] is the set of the LR(0) items in the LR(0) core of the LR(1)
POTTIER Francois's avatar
POTTIER Francois committed
193 194
     state [s]. This set is not epsilon-closed. This set is presented as a
     list, in an arbitrary order. *)
195 196

  val items: 'a lr1state -> item list
197

198 199 200 201 202 203
  (* [nullable nt] tells whether the non-terminal symbol [nt] is nullable.
     That is, it is true if and only if this symbol produces the empty
     word [epsilon]. *)

  val nullable: 'a nonterminal -> bool

204 205 206 207 208 209
  (* [first nt t] tells whether the FIRST set of the nonterminal symbol [nt]
     contains the terminal symbol [t]. That is, it is true if and only if
     [nt] produces a word that begins with [t]. *)

  val first: 'a nonterminal -> 'b terminal -> bool

210 211 212 213 214 215 216
  (* [foreach_terminal] enumerates the terminal symbols, including [error].
     [foreach_terminal_but_error] enumerates the terminal symbols, excluding
     [error]. *)

  val foreach_terminal:           (xsymbol -> 'a -> 'a) -> 'a -> 'a
  val foreach_terminal_but_error: (xsymbol -> 'a -> 'a) -> 'a -> 'a

217 218
end

219 220 221 222 223 224 225 226 227 228 229 230
(* This signature combines the incremental API and the inspection API. *)

module type EVERYTHING = sig

  include INCREMENTAL_ENGINE

  include INSPECTION
    with type 'a lr1state := 'a lr1state
    with type production := production

end