package containers

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package containers
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Very Simple Parser Combinators

Examples:

parse recursive structures
open Containers_string.Parse;;

type tree = L of int | N of tree * tree;;

let mk_leaf x = L x
let mk_node x y = N(x,y)

let ptree = fix @@ fun self ->
  skip_space *>
  ( (char '(' *> (pure mk_node <*> self <*> self) <* char ')')
    <|>
    (U.int >|= mk_leaf) )
;;

parse_string_exn "(1 (2 3))" ptree;;
parse_string_exn "((1 2) (3 (4 5)))" ptree;;
Parse a list of words
open Containers_string.Parse;;
let p = U.list ~sep:"," U.word;;
parse_string_exn "[abc , de, hello ,world  ]" p;;
  • since 0.11
type 'a or_error = [
  1. | `Ok of 'a
  2. | `Error of string
]
type line_num = int
  • since 0.13
type col_num = int
  • since 0.13
  • since 0.13
exception ParseError of line_num * col_num * unit -> string

position * message

This type changed at 0.13

Input

module MemoTbl : sig ... end
type input = {
  1. is_done : unit -> bool;
    (*

    End of input?

    *)
  2. cur : unit -> char;
    (*

    Current char

    *)
  3. next : unit -> char;
    (*

    Returns current char; if not is_done, move to next char, otherwise throw ParseError

    *)
  4. pos : unit -> int;
    (*

    Current pos

    *)
  5. lnum : unit -> line_num;
    (*

    Line number

    • since 0.13
    *)
  6. cnum : unit -> col_num;
    (*

    column number

    • since 0.13
    *)
  7. memo : MemoTbl.t;
    (*

    memoization table, if any

    *)
  8. backtrack : int -> unit;
    (*

    Restore to previous pos

    *)
  9. sub : int -> int -> string;
    (*

    sub pos len extracts slice from pos with len

    *)
}

The type of input, which must allow for backtracking somehow. This type is unstable and its details might change.

val input_of_string : string -> input

Parse the string

val input_of_chan : ?size:int -> in_channel -> input

input_of_chan ic reads lazily the content of ic as parsing goes. All content that is read is saved to an internal buffer for backtracking.

  • parameter size

    number of bytes read at once from ic

  • since 0.13

Combinators

type 'a t = input -> 'a
val return : 'a -> 'a t

Always succeeds, without consuming its input

val pure : 'a -> 'a t

synonym to return

val (>|=) : 'a t -> ('a -> 'b) -> 'b t

Map

val (>>=) : 'a t -> ('a -> 'b t) -> 'b t

Monadic bind

val (<*>) : ('a -> 'b) t -> 'a t -> 'b t

Applicative

val (<*) : 'a t -> _ t -> 'a t

a <* b parses a into x, parses b and ignores its result, and returns x

val (*>) : _ t -> 'a t -> 'a t

a *> b parses a, then parses b into x, and returns x. The results of a is ignored.

val fail : string -> 'a t

fail msg fails with the given message. It can trigger a backtrack

val eoi : unit t

Expect the end of input, fails otherwise

val nop : unit t

Succeed with ()

val char : char -> char t

char c parses the char c and nothing else

val char_if : (char -> bool) -> char t

char_if f parses a character c if f c = true

val chars_if : (char -> bool) -> string t

chars_if f parses a string of chars that satisfy f

val chars1_if : (char -> bool) -> string t

Same as chars_if, but only non-empty strings

val endline : char t

Parses '\n'

val space : char t

tab or space

val white : char t

tab or space or newline

val skip_chars : (char -> bool) -> unit t

Skip 0 or more chars satisfying the predicate

val skip_space : unit t

Skip ' ' and '\t'

val skip_white : unit t

Skip ' ' and '\t' and '\n'

val is_alpha : char -> bool

Is the char a letter?

val is_num : char -> bool

Is the char a digit?

val is_alpha_num : char -> bool
val is_space : char -> bool

True on ' ' and '\t'

val is_white : char -> bool

True on ' ' and '\t' and '\n'

  • since 0.13
val (~~~) : (char -> bool) -> char -> bool

Negation on predicates

val (|||) : (char -> bool) -> (char -> bool) -> char -> bool

Disjunction on predicates

val (&&&) : (char -> bool) -> (char -> bool) -> char -> bool

Conjunction on predicates

val (<|>) : 'a t -> 'a t -> 'a t

a <|> b tries to parse a, and if a fails, backtracks and tries to parse b. Therefore, it succeeds if either succeeds

val string : string -> string t

string s parses exactly the string s, and nothing else

val many : 'a t -> 'a list t

many p parses a list of p, eagerly (as long as possible)

val many1 : 'a t -> 'a list t

parses a non empty list

val skip : _ t -> unit t

skip p parses p and ignores its result

val sep : by:_ t -> 'a t -> 'a list t

sep ~by p parses a list of p separated by by

val sep1 : by:_ t -> 'a t -> 'a list t

sep1 ~by p parses a non empty list of p, separated by by

val fix : ('a t -> 'a t) -> 'a t

Fixpoint combinator

val memo : 'a t -> 'a t

Memoize the parser. memo p will behave like p, but when called in a state (read: position in input) it has already processed, memo p returns a result directly. The implementation uses an underlying hashtable. This can be costly in memory, but improve the run time a lot if there is a lot of backtracking involving p.

This function is not thread-safe.

  • since 0.13
val fix_memo : ('a t -> 'a t) -> 'a t

Same as fix, but the fixpoint is memoized.

  • since 0.13

Parse

val parse : input:input -> 'a t -> 'a or_error

parse ~input p applies p on the input, and returns `Ok x if p succeeds with x, or `Error s otherwise

val parse_exn : input:input -> 'a t -> 'a
val parse_string : string -> 'a t -> 'a or_error

Specialization of parse for string inputs

val parse_string_exn : string -> 'a t -> 'a
val parse_file : ?size:int -> file:string -> 'a t -> 'a or_error

parse_file ~file p parses file with p by opening the file and using input_of_chan.

  • parameter size

    size of chunks read from file

  • since 0.13
val parse_file_exn : ?size:int -> file:string -> 'a t -> 'a

Unsafe version of parse_file

  • since 0.13

Utils

module U : sig ... end
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