https://github.com/Ahnfelt/parsercombinator

A parser combinator for Java 8. Proof of concept.
https://github.com/Ahnfelt/parsercombinator

Last synced: 21 days ago
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A parser combinator for Java 8. Proof of concept.

• Host: GitHub
• URL: https://github.com/Ahnfelt/parsercombinator
• Owner: Ahnfelt
• Created: 2015-03-03T05:56:49.000Z (over 9 years ago)
• Default Branch: master
• Last Pushed: 2020-10-13T11:16:11.000Z (about 4 years ago)
• Last Synced: 2024-07-31T21:54:48.880Z (4 months ago)
• Language: Java
• Size: 13.7 KB
• Stars: 13
• Watchers: 2
• Forks: 3
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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• awesome-combinator-parsers - Ahnfelt/parsercombinator

README

        
# parsercombinator

A parser combinator for Java 8. Working, but mostly a proof of concept.

```java

import static dk.ahnfelt.parsercombinator.Parsers.*;

```

```java

Parser parseFoo = string("foo");

parseFoo.parse("foo") // returns "foo"

parseFoo.parse("bar") // throws Parsers.Failure

```

```java

Parser parseIntegerMatch = regex("[0-9]+").map(m -> Integer.parseInt(m.group()));

parseFoo.parse("42") // returns "42"

parseFoo.parse("bar") // throws Parsers.Failure

```

```java

Parser> parseFooN = parseFoo.then(parseInteger);

parseFoo.parse("foo7") // returns ("foo", 7)

```

```java

Parser parseFooN2 = skip(parseFoo).then(parseInteger);

parseFooN2.parse("foo7") // returns 7

```

```java

Parser parseFooOrBar = choice(string("foo"), string("bar"));

parseFoo.parse("foo") // returns "foo"

parseFoo.parse("bar") // returns "bar"

parseFoo.parse("quux") // throws Parsers.Failure

```

```java

// Alternative version of the above

Parser parseFooOrBar2 = 

    regex("[a-z]+").

    map(m -> m.group()).

    filter(t -> t.equals("foo") || t.equals("bar"));

```

```java

Parser> parsePlus = 

    parseInteger.

    skip(string("+")).

    then(parseInteger);

Parser parseAndCompute = parsePlus.map(match((x, y) -> x + y));

parseAndCompute.parse("7+3") // returns 10

```

```java

Parser> parseList = parseInteger.zeroOrMore(string(","));

parseList.parse("1,2,4,8,16,32") // returns [1, 2, 4, 8, 16, 32]

```

```java

Parser parseToken = regex("\\s*([a-z0-9]+)\\s*").map(m -> m.group(1));

Parser keyword(String name) { return parseToken.filter(t -> t.equals(name)); }

// The nested pairs can get hairy - use .map(match(...)) to get rid of them before you have to write types like this:

Parser<, Optional>> parseIf = 

    skip(keyword("if")).then(parseToken).

    skip(keyword("then")).then(parseToken).

    then(skip(keyword("else")).then(parseToken).optional()).

    skip(keyword("end"));

parseIf.parse("if x then y else z end") // returns (("x", "y"), Optional["z"])

Parser parseIfAndCompute = 

    parseIf.map(match((x, y, z) -> x.equals("true") ? y : z.orElse("void")));

parseIfAndCompute.parse("if true then y else z end") // returns "y"

parseIfAndCompute.parse("if false then y end") // returns "void"

```