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 ;
57
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  co-re‐
91       sponsible  for  properly  updating the position fields, as described in
92       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 en‐
101       gine  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 set_position : lexbuf -> position -> unit
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139       Set  the  initial  tracked input position for lexbuf to a custom value.
140       Ignores pos_fname . See Lexing.set_filename for changing this field.
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143       Since 4.11
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147       val set_filename : lexbuf -> string -> unit
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149       Set filename in the initial tracked position to file in lexbuf .
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152       Since 4.11
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156       val with_positions : lexbuf -> bool
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158       Tell whether the lexer buffer keeps track of position fields lex_curr_p
159       /  lex_start_p  ,  as determined by the corresponding optional argument
160       for functions that create lexer buffers (whose default value is true ).
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162       When with_positions is false , lexer actions should not modify position
163       fields.   Doing  it nevertheless could re-enable the with_position mode
164       and degrade performances.
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169   Functions for lexer semantic actions
170       The following functions can be called  from  the  semantic  actions  of
171       lexer  definitions  (the  ML  code enclosed in braces that computes the
172       value returned by lexing functions). They give access to the  character
173       string  matched  by the regular expression associated with the semantic
174       action. These functions must be applied to the argument lexbuf , which,
175       in the code generated by ocamllex , is bound to the lexer buffer passed
176       to the parsing function.
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178       val lexeme : lexbuf -> string
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181       Lexing.lexeme lexbuf returns the string matched by the regular  expres‐
182       sion.
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186       val lexeme_char : lexbuf -> int -> char
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189       Lexing.lexeme_char  lexbuf  i returns character number i in the matched
190       string.
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194       val lexeme_start : lexbuf -> int
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197       Lexing.lexeme_start lexbuf returns the offset in the  input  stream  of
198       the  first character of the matched string.  The first character of the
199       stream has offset 0.
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203       val lexeme_end : lexbuf -> int
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206       Lexing.lexeme_end lexbuf returns the offset in the input stream of  the
207       character following the last character of the matched string. The first
208       character of the stream has offset 0.
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212       val lexeme_start_p : lexbuf -> position
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214       Like lexeme_start , but return a complete position instead of  an  off‐
215       set.    When  position  tracking  is  disabled,  the  function  returns
216       dummy_pos .
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220       val lexeme_end_p : lexbuf -> position
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222       Like lexeme_end , but return a complete position instead of an  offset.
223       When position tracking is disabled, the function returns dummy_pos .
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227       val new_line : lexbuf -> unit
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229       Update the lex_curr_p field of the lexbuf to reflect the start of a new
230       line.  You can call this function in the semantic action  of  the  rule
231       that matches the end-of-line character.  The function does nothing when
232       position tracking is disabled.
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235       Since 3.11.0
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240   Miscellaneous functions
241       val flush_input : lexbuf -> unit
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243       Discard the contents of the buffer and reset the current position to 0.
244       The next use of the lexbuf will trigger a refill.
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250OCamldoc                          2021-01-26                  Stdlib.Lexing(3)
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