Module Fmlib_parse.Position

Represent a position in a text file.

A position in a text file is represented by a line number and a column number, both starting with zero. So the first line is line number zero and the first column is column number zero.

Sometimes the absolute byte offset since the beginning of the file is important. Therefore the absolute byte offset for the last newline is included as well.

Furthermore it is important to distinguish between the byte position and the character position within a line. Therefore a correction offset is needed which is added to the byte column to get the character column.

An object of type Position.t has the following content:

By default all bytes between space and ascii 126 and between decimal 128 and decimal 255 are treated as one character. The tab character is treated as 4 characters and the newline character increments the line number and resets the column number. All other bytes between decimal 0 and before the space are treated as zero characters.

This default handling is done by the function next. For more special treatments (e.g. unicode characters) there is the function correct to adapt the character position with respect to the by position and the functions advance and newline for find granular control of the position.

Basics

type t

Position in a text file.

val start : t

Position with points to the start of a textfile (line = 0, column = 0).

Line and column number

val line : t -> int

line pos The line number corresponding to the position p. Note: The first line is line 0.

val column : t -> int

column pos The character position within the current line of pos.

For differences between column and byte_column see byte_column.

Note: The first column is column 0.

Byte offsets

val byte_offset_bol : t -> int

byte_offset_bol pos The byte offset since the beginning of the file at the last newline.

val byte_column : t -> int

byte_column pos The byte column number corresponding to the position p.

Note: If the line up to the position has only printable ascii or latin-1 characters, then the byte_column p is the same as column p. If the line has some multibyte unicode characters, then both columns might be different. Notprintable ascii characters i.e. characters before the space character increase the byte column, but not the column.

val byte_offset : t -> int

byte_offset pos The byte offset of the current position since the beginning of the file.

Increment position

val next : char -> t -> t

next next_char pos: Advance the position by using the next character. If the next character is a newline, then the line number is increment and the column number is reset to 0.

val correct : int -> t -> t

correct n pos Correct the column by n. In case of multibyte characters like unicode characters the correction must be negative.

val advance : int -> int -> t -> t

advance byte_width width pos Advance the position by byte_width and character width width.

val newline : int -> t -> t

newline byte_width pos Start a new line i.e. set the character position and byte position to zero and increment the line number.

Compare positions

val is_less_equal : t -> t -> bool

is_less_equal p1 p2 Are p1 and p2 in the correct order i.e. p2 is not before p1.

Ranges (i.e. pairs of positions)

type range = t * t
val is_valid_range : range -> bool

Is the range a valid range in a file i.e. are both positions valid and is the first position before or at the second position?

val merge : range -> range -> range

merge range_1 range_2

Merge the ranges range_1 and range_2 the result range has the maximum span of both. I.e. the merges selects as start position the lowest position of both and as end position the highest position of both. I.e. the merges selects as start position the lowest position of both and as end position the highest position of both.