1Stdlib.Lexing(3)                 OCaml library                Stdlib.Lexing(3)
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NAME

6       Stdlib.Lexing - no description
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Module

9       Module   Stdlib.Lexing
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Documentation

12       Module Lexing
13        : (module Stdlib__lexing)
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23   Positions
24       type position = {
25        pos_fname : string ;
26        pos_lnum : int ;
27        pos_bol : int ;
28        pos_cnum : int ;
29        }
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32       A value of type position describes a point in a source file.  pos_fname
33       is the file name; pos_lnum is the line number; pos_bol is the offset of
34       the  beginning  of the line (number of characters between the beginning
35       of the lexbuf and the beginning of the line); pos_cnum is the offset of
36       the  position (number of characters between the beginning of the lexbuf
37       and the position).  The difference between pos_cnum and pos_bol is  the
38       character offset within the line (i.e. the column number, assuming each
39       character is one column wide).
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41       See the documentation of type lexbuf for information about how the lex‐
42       ing engine will manage positions.
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46       val dummy_pos : position
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48       A  value  of  type position , guaranteed to be different from any valid
49       position.
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54   Lexer buffers
55       type lexbuf = {
56        refill_buff : lexbuf -> unit ;
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58       mutable lex_buffer : bytes ;
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60       mutable lex_buffer_len : int ;
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62       mutable lex_abs_pos : int ;
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64       mutable lex_start_pos : int ;
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66       mutable lex_curr_pos : int ;
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68       mutable lex_last_pos : int ;
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70       mutable lex_last_action : int ;
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72       mutable lex_eof_reached : bool ;
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74       mutable lex_mem : int array ;
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76       mutable lex_start_p : position ;
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78       mutable lex_curr_p : position ;
79        }
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82       The type of lexer buffers. A lexer buffer is the argument passed to the
83       scanning functions defined by the generated scanners.  The lexer buffer
84       holds the current state of the scanner, plus a function to  refill  the
85       buffer from the input.
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87       Lexers  can optionally maintain the lex_curr_p and lex_start_p position
88       fields.  This "position tracking" mode is the default,  and  it  corre‐
89       sponds  to  passing  ~with_position:true to functions that create lexer
90       buffers. In  this  mode,  the  lexing  engine  and  lexer  actions  are
91       co-responsible  for properly updating the position fields, as described
92       in the next paragraph.  When the  mode  is  explicitly  disabled  (with
93       ~with_position:false  ),  the lexing engine will not touch the position
94       fields and the lexer actions should be careful not to do it either; the
95       lex_curr_p  and  lex_start_p  field will then always hold the dummy_pos
96       invalid position.  Not tracking positions avoids allocations and memory
97       writes  and  can  significantly improve the performance of the lexer in
98       contexts where lex_start_p and lex_curr_p are not needed.
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100       Position tracking mode works as follows.  At  each  token,  the  lexing
101       engine  will  copy lex_curr_p to lex_start_p , then change the pos_cnum
102       field of lex_curr_p by updating it with the number of  characters  read
103       since the start of the lexbuf .  The other fields are left unchanged by
104       the lexing engine.  In order to keep them accurate, they must  be  ini‐
105       tialised  before  the first use of the lexbuf, and updated by the rele‐
106       vant lexer actions (i.e. at each end of line -- see also new_line ).
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110       val from_channel : ?with_positions:bool -> in_channel -> lexbuf
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112       Create a lexer buffer on the given input channel.   Lexing.from_channel
113       inchan returns a lexer buffer which reads from the input channel inchan
114       , at the current reading position.
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118       val from_string : ?with_positions:bool -> string -> lexbuf
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120       Create a lexer buffer which reads from the given string. Reading starts
121       from  the  first  character in the string. An end-of-input condition is
122       generated when the end of the string is reached.
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126       val from_function : ?with_positions:bool -> (bytes -> int  ->  int)  ->
127       lexbuf
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129       Create  a  lexer  buffer with the given function as its reading method.
130       When the scanner needs more characters, it will call  the  given  func‐
131       tion,  giving  it  a  byte sequence s and a byte count n . The function
132       should put n bytes or fewer in s , starting at index 0, and return  the
133       number of bytes provided. A return value of 0 means end of input.
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137       val with_positions : lexbuf -> bool
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139       Tell whether the lexer buffer keeps track of position fields lex_curr_p
140       / lex_start_p , as determined by the  corresponding  optional  argument
141       for functions that create lexer buffers (whose default value is true ).
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143       When with_positions is false , lexer actions should not modify position
144       fields.  Doing it nevertheless could re-enable the  with_position  mode
145       and degrade performances.
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150   Functions for lexer semantic actions
151       The  following  functions  can  be  called from the semantic actions of
152       lexer definitions (the ML code enclosed in  braces  that  computes  the
153       value  returned by lexing functions). They give access to the character
154       string matched by the regular expression associated with  the  semantic
155       action. These functions must be applied to the argument lexbuf , which,
156       in the code generated by ocamllex , is bound to the lexer buffer passed
157       to the parsing function.
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159       val lexeme : lexbuf -> string
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162       Lexing.lexeme  lexbuf returns the string matched by the regular expres‐
163       sion.
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167       val lexeme_char : lexbuf -> int -> char
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170       Lexing.lexeme_char lexbuf i returns character number i in  the  matched
171       string.
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175       val lexeme_start : lexbuf -> int
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178       Lexing.lexeme_start  lexbuf  returns  the offset in the input stream of
179       the first character of the matched string.  The first character of  the
180       stream has offset 0.
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184       val lexeme_end : lexbuf -> int
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187       Lexing.lexeme_end  lexbuf returns the offset in the input stream of the
188       character following the last character of the matched string. The first
189       character of the stream has offset 0.
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193       val lexeme_start_p : lexbuf -> position
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195       Like  lexeme_start  , but return a complete position instead of an off‐
196       set.   When  position  tracking  is  disabled,  the  function   returns
197       dummy_pos .
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201       val lexeme_end_p : lexbuf -> position
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203       Like  lexeme_end , but return a complete position instead of an offset.
204       When position tracking is disabled, the function returns dummy_pos .
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208       val new_line : lexbuf -> unit
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210       Update the lex_curr_p field of the lexbuf to reflect the start of a new
211       line.   You  can  call this function in the semantic action of the rule
212       that matches the end-of-line character.  The function does nothing when
213       position tracking is disabled.
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216       Since 3.11.0
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221   Miscellaneous functions
222       val flush_input : lexbuf -> unit
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224       Discard the contents of the buffer and reset the current position to 0.
225       The next use of the lexbuf will trigger a refill.
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231OCamldoc                          2020-02-27                  Stdlib.Lexing(3)