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

6       Lexing - The run-time library for lexers generated by ocamllex.
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Module

9       Module   Lexing
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Documentation

12       Module Lexing
13        : sig end
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16       The run-time library for lexers generated by ocamllex .
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24       === Positions ===
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27       type position = {
28        pos_fname : string ;
29        pos_lnum : int ;
30        pos_bol : int ;
31        pos_cnum : int ;
32        }
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35       A value of type position describes a point in a source file.  pos_fname
36       is the file name; pos_lnum is the line number; pos_bol is the offset of
37       the  beginning  of the line (number of characters between the beginning
38       of the lexbuf and the beginning of the line); pos_cnum is the offset of
39       the  position (number of characters between the beginning of the lexbuf
40       and the position).  The difference between pos_cnum and pos_bol is  the
41       character offset within the line (i.e. the column number, assuming each
42       character is one column wide).
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44       See the documentation of type lexbuf for information about how the lex‐
45       ing engine will manage positions.
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49       val dummy_pos : position
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51       A  value  of  type position , guaranteed to be different from any valid
52       position.
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57       === Lexer buffers ===
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60       type lexbuf = {
61        refill_buff : lexbuf -> unit ;
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63       mutable lex_buffer : bytes ;
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65       mutable lex_buffer_len : int ;
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67       mutable lex_abs_pos : int ;
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69       mutable lex_start_pos : int ;
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71       mutable lex_curr_pos : int ;
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73       mutable lex_last_pos : int ;
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75       mutable lex_last_action : int ;
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77       mutable lex_eof_reached : bool ;
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79       mutable lex_mem : int array ;
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81       mutable lex_start_p : position ;
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83       mutable lex_curr_p : position ;
84        }
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87       The type of lexer buffers. A lexer buffer is the argument passed to the
88       scanning functions defined by the generated scanners.  The lexer buffer
89       holds the current state of the scanner, plus a function to  refill  the
90       buffer from the input.
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92       At  each token, the lexing engine will copy lex_curr_p to lex_start_p ,
93       then change the pos_cnum field of lex_curr_p by updating  it  with  the
94       number  of  characters  read since the start of the lexbuf .  The other
95       fields are left unchanged by the lexing engine.  In order to keep  them
96       accurate,  they must be initialised before the first use of the lexbuf,
97       and updated by the relevant lexer actions (i.e. at each end of line  --
98       see also new_line ).
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102       val from_channel : Pervasives.in_channel -> lexbuf
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104       Create  a lexer buffer on the given input channel.  Lexing.from_channel
105       inchan returns a lexer buffer which reads from the input channel inchan
106       , at the current reading position.
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110       val from_string : string -> lexbuf
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112       Create a lexer buffer which reads from the given string. Reading starts
113       from the first character in the string. An  end-of-input  condition  is
114       generated when the end of the string is reached.
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118       val from_function : (bytes -> int -> int) -> lexbuf
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120       Create  a  lexer  buffer with the given function as its reading method.
121       When the scanner needs more characters, it will call  the  given  func‐
122       tion,  giving  it  a  byte sequence s and a byte count n . The function
123       should put n bytes or fewer in s , starting at index 0, and return  the
124       number of bytes provided. A return value of 0 means end of input.
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129       === Functions for lexer semantic actions ===
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132       ===  The following functions can be called from the semantic actions of
133       lexer definitions (the ML code enclosed in  braces  that  computes  the
134       value  returned by lexing functions). They give access to the character
135       string matched by the regular expression associated with  the  semantic
136       action.  These functions must be applied to the argument lexbuf, which,
137       in the code generated by ocamllex, is bound to the lexer buffer  passed
138       to the parsing function. ===
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141       val lexeme : lexbuf -> string
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144       Lexing.lexeme  lexbuf returns the string matched by the regular expres‐
145       sion.
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149       val lexeme_char : lexbuf -> int -> char
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152       Lexing.lexeme_char lexbuf i returns character number i in  the  matched
153       string.
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157       val lexeme_start : lexbuf -> int
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160       Lexing.lexeme_start  lexbuf  returns  the offset in the input stream of
161       the first character of the matched string.  The first character of  the
162       stream has offset 0.
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166       val lexeme_end : lexbuf -> int
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169       Lexing.lexeme_end  lexbuf returns the offset in the input stream of the
170       character following the last character of the matched string. The first
171       character of the stream has offset 0.
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175       val lexeme_start_p : lexbuf -> position
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177       Like  lexeme_start  , but return a complete position instead of an off‐
178       set.
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182       val lexeme_end_p : lexbuf -> position
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184       Like lexeme_end , but return a complete position instead of an offset.
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188       val new_line : lexbuf -> unit
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190       Update the lex_curr_p field of the lexbuf to reflect the start of a new
191       line.   You  can  call this function in the semantic action of the rule
192       that matches the end-of-line character.
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195       Since 3.11.0
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200       === Miscellaneous functions ===
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203       val flush_input : lexbuf -> unit
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205       Discard the contents of the buffer and reset the current position to 0.
206       The next use of the lexbuf will trigger a refill.
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212OCamldoc                          2019-02-02                         Lexing(3)