package containers

  1. Overview
  2. Docs
package containers
Legend:
Library
Module
Module type
Parameter
Class
Class type

Very Simple Parser Combinators

open CCParse;;

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 *>
    ( (try_ (char '(') *> (pure mk_node <*> self <*> self) <* char ')')
      <|>
        (U.int >|= mk_leaf) )
;;

parse_string_exn ptree "(1 (2 3))" ;;
parse_string_exn ptree "((1 2) (3 (4 5)))" ;;
Parse a list of words
open Containers.Parse;;
let p = U.list ~sep:"," U.word;;
parse_string_exn p "[abc , de, hello ,world  ]";;
Stress Test

This makes a list of 100_000 integers, prints it and parses it back.

let p = CCParse.(U.list ~sep:"," U.int);;

let l = CCList.(1 -- 100_000);;
let l_printed =
  CCFormat.(to_string (within "[" "]" (list ~sep:(return ",@,") int))) l;;

let l' = CCParse.parse_string_exn p l_printed;;

assert (l=l');;
type 'a or_error = ('a, string) Stdlib.result
type line_num = int
type col_num = int
type parse_branch
val string_of_branch : parse_branch -> string
exception ParseError of parse_branch * unit -> string

parsing branch * message.

Input

type position
type state
val state_of_string : string -> state

Combinators

type 'a t = state -> ok:('a -> unit) -> err:(exn -> unit) -> unit

Takes the input and two continuations:

  • ok to call with the result when it's done
  • err to call when the parser met an error
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 map : ('a -> 'b) -> 'a t -> 'b t
val map2 : ('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t
val map3 : ('a -> 'b -> 'c -> 'd) -> 'a t -> 'b t -> 'c t -> 'd t
val (>>=) : 'a t -> ('a -> 'b t) -> 'b t

Monadic bind. p >>= f results in a new parser which behaves as p then, in case of success, applies f to the result.

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 failf : ('a, unit, string, 'b t) Stdlib.format4 -> 'a

Format.sprintf version of fail.

val parsing : string -> 'a t -> 'a t

parsing s p behaves the same as p, with the information that we are parsing s, if p fails.

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 character 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

Like chars_if, but only non-empty strings.

val endline : char t

Parse '\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

Is the char a letter or a digit?

val is_space : char -> bool

True on ' ' and '\t'.

val is_white : char -> bool

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

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

a <|> b tries to parse a, and if a fails without consuming any input, backtracks and tries to parse b, otherwise it fails as a. See try_ to ensure a does not consume anything (but it is best to avoid wrapping large parsers with try_).

val (<?>) : 'a t -> string -> 'a t

a <?> msg behaves like a, but if a fails without consuming any input, it fails with msg instead. Useful as the last choice in a series of <|>: a <|> b <|> c <?> "expected a|b|c".

val try_ : 'a t -> 'a t

try_ p tries to parse like p, but backtracks if p fails. Useful in combination with <|>.

val suspend : (unit -> 'a t) -> 'a t

suspend f is the same as f (), but evaluates f () only when needed.

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

Parse a non-empty list.

val skip : _ t -> unit t

skip p parses zero or more times 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.

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

Like fix, but the fixpoint is memoized.

val get_lnum : int t

Reflect the current line number.

val get_cnum : int t

Reflect the current column number.

val get_pos : (int * int) t

Reflect the current (line, column) numbers.

Parse

Those functions have a label ~p on the parser, since 0.14.

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

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

val parse_exn : 'a t -> state -> 'a

Unsafe version of parse.

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

Specialization of parse for string inputs.

val parse_string_exn : 'a t -> string -> 'a
val parse_file : 'a t -> string -> 'a or_error

parse_file p file parses file with p by opening the file and reading it whole.

val parse_file_exn : 'a t -> string -> 'a

Infix

module Infix : sig ... end

Utils

This is useful to parse OCaml-like values in a simple way.

module U : sig ... end

Let operators on OCaml >= 4.08.0, nothing otherwise

  • since 2.8
include CCShimsMkLet_.S with type 'a t_let := 'a t
OCaml

Innovation. Community. Security.

GitHub Discord Twitter Peertube RSS
About
Changelog Releases Industrial Users Academic Users Why OCaml
Ecosystem
Packages Community Events OCaml Planet Jobs
Resources
Install OCaml Get Started Platform Tools Language Manual Standard Library API Books Exercises Papers OCaml Playground Logo
Policies
Carbon Footprint Governance Privacy Code of Conduct