Mopclip : human-friendly monadic parser-combinator library

Example:

Simple csv parser:

open Mopclip;

val cell = (manyC anyCharP) mapP implode;
val line = cell sepBy (charP #",");
val csv = line sepBy (charP #"\n");

(* To apply this parser, we'll use runParser function *)
runParser csv "meow,meow\nmeow,nmeow";
- val it = Success ([["meow","meow"],["meow","nmeow"]],"")

Overview of MLB files

• lib/github.com/poipoiPIO/mopclip/mopclip.mlb:

  • signature Mopclip

Use of the package

This library is set up to work well with the SML package manager smlpkg. To use the package, in the root of your project directory, execute the command:

$ smlpkg add github.com/poipoiPIO/mopclip

And then sync your packages locally using the following command:

$ smlpkg sync

You can now reference the mlb-file using relative paths from within your project's mlb-files.

API reference:

Types:

pResult:

datatype 'a pResult = Failure of string | Success of 'a

The result type of parsing application

parser type:

datatype 'a parser = Parser of string -> ('a * string)

Generalized type of any parser in a library.

Parsers:

charP:

charP : char -> char parser;

simply parses character, for example: val eol = charP #"\n";

anyOf:

anyOf : char list -> char parser;

Simply parse one of the characters in a list

digitP:

digitP : char parser;

Parsing a digit:

val string_to_parse = "1,2,meow";

runParser digitP string_to_parse;
- val it = Success (#"1",",2,meow")

stringP:

stringP : string -> string parser;

Parses string: val meowP = stringP "meow";

anyCharP:

anyCharP : char parser

Parse an alphabet character in any register

Combinators:

errorC:

errorC : string -> 'a parser -> 'a parser

Adds a label to parser Failure message:

val string_to_parse = ",2,meow";
val digit_parser_with_error = errorC "Digit" digitP;

runParser digit_parser_with_error string_to_parse;
- val it = Failure "Digit :: Excepted character: 9, But: , was found"

(* let's fail parser without the error label*)
runParser digitP string_to_parse;
- val it = Failure "Excepted character: 9, But: , was found"

Basic parser combinators:

infix andThen : 'a parser -> 'b parser -> ('a * 'b) parser

Sequentially run parsers and returns the result of parser application

infix orElse : 'a parser -> 'a parser -> 'a parser

Run the first parser and if it fails return the result of the second one

infix orElseL : (unit -> 'a parser) -> (unit -> 'a parser) -> 'a parser

Run the first parser and if it fails return the result of the second one Similar to orElse parser, but uses arguments wrapped in the lambda abstraction for lazy-semantics needed for combinators recursion.

mapP:

infix mapP : 'a parser -> ('a -> 'b) -> 'b parser

Applies a function to the parser result and wraps it in parser type

manyC:

manyC : 'a parser -> 'a list parser

Applies parser as many as it succeeds and returns the list of results as the result

val manyDigits = manyC digitP;

many1C : 'a parser -> 'a list parser

It has the same behavior as the manyC combinator, but required at least one successful 'a parser application to parse successefully

sepBy:

infix sepBy : 'a parser -> 'b parser -> 'a list parser

Parse sequence of parsers separated by the parser. As the demo, you might look in the csv-parser example above.

infix sepBy1 : 'a parser -> 'b parser -> 'a list parser

It has the same behavior as the sepBy, but required at least one sepBy unit to parse successfully

Applicatives:

Let's write some parsers using applicative operations!

- val digitArrayP = 
    ((charP #"[")
      *> (manyC (digitP <* (charP #",")))
      <* (charP #"]"))
      mapP (map (fn c => (ord c) - 48));


##### Applicatives:
runParser digitArrayP "[1,2,3,]";
- val it = Success ([1,2,3],"")

p1 <* p2 - means that we apply p1, then apply p2, and return the result of p1 and the rest of the parsing

p1 *> p2 - apply the first parser, apply the second parser, and return the result of the second one

Monadic operations:

Just a bunch of standard monadic operations needed to combine parsers

infix >>= : 'a parser -> ('a -> 'b parser) -> 'b parser

infix >>> : 'a parser -> 'b parser -> 'b parser

Simple interpreter using Mopclip:

https://gist.github.com/poipoiPIO/e202cba9d08dfa4d7a3b9556384950ee