Headline

An ANTLR-based parser with semantic actions

Characteristics

An Technology:ANTLR-based parser for a concrete syntax of companies is provided. The underlying grammar is LL(1). The parser uses semantics actions to implement Feature:Total.

Illustration

The data model is implemented as plain textual files:

company "ACME Corporation" { department "Research" { manager "Craig" { address "Redmond" salary 123456.0 } employee "Erik" { address "Utrecht" salary 12345.0 } employee "Ralf" { address "Koblenz" salary 1234.0 } } department "Development" { manager "Ray" { address "Redmond" salary 234567.0 } department "Dev1" { manager "Klaus" { address "Boston" salary 23456.0 } department "Dev1.1" { manager "Karl" { address "Riga" salary 2345.0 } employee "Joe" { address "Wifi City" salary 2344.0 } } } } }

A Parser for Feature:Company will be generated by Technology:ANTLR using src/main/antlr/Company.g.

A Company is defined by:

company :
  'company' STRING '{' department* '}' EOF;
  
department :
  'department' STRING '{' 
    'manager' employee
    ('employee' employee)* 
    department*
  '}';

employee :
  STRING '{'
    'address' STRING
    'salary' FLOAT 
    { total += Double.parseDouble($FLOAT.text); }
  '}';

STRING  :   '"' (~'"')* '"';
FLOAT   :   ('0'..'9')+ ('.' ('0'..'9')+)?;
WS      :   (' '|'\r'? '\n'|'\t')+ {skip();};

Feature:Parsing is implemented using the generated Parser:

package org.softlang.company.features;

import org.softlang.company.antlr.CompanyLexer;
import org.softlang.company.antlr.CompanyParser;

import org.antlr.runtime.*;

import java.io.FileInputStream;
import java.io.IOException;

public class Parsing {

    public static CompanyParser parse(String s)
            throws IOException, RecognitionException {
        FileInputStream stream = new FileInputStream(s);
        ANTLRInputStream antlr = new ANTLRInputStream(stream);
        CompanyLexer lexer = new CompanyLexer(antlr);
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        CompanyParser parser = new CompanyParser(tokens);
        parser.company();
        if (parser.error) throw new RecognitionException();
        return parser;
    }

}

Feature:Total is implemented as part of Feature:Parsing with a semantic action (see Company.g):

employee :
  STRING '{'
    'address' STRING
    'salary' FLOAT 
    { total += Double.parseDouble($FLOAT.text); }
  '}';

    public static double total(String s)
            throws IOException, RecognitionException {
        /* 
         * Total is implemented by the generated Parser 
         * See src/main/antlr/Company.g
         */
        CompanyParser parser = Parsing.parse(s);
        return parser.total;
    }

Test cases are implemented for all Namespace:Features. There is also an invalid input:

company "foobar" { department "barfoo" { } }

Relationships

This contribution shows Feature:Parsing with semantic actions using Technology:ANTLR and Language:Java

For an ANTLER4 version see Contribution:antlr4Parser.

For plain syntax checking see Contribution:antlrAcceptor.

For a basic example of lexing/tokenization see Contribution:antlrLexer.

For Object-Text mapping with Technology:ANTLR see Contribution:antlrObjects.

For walking a parsed Feature:Company-tree with Technology:ANTLR see Contribution:antlrTrees.

Architecture

The contribution follows a standardized structure:

  • inputs contains input files for tests
  • src/main/antlr contains grammar files for Technology:ANTLR.
  • src/main/java contains the following packages:
  • src/test/java contains the following packages:

Usage

This contribution uses Technology:Gradle for building. Technology:Eclipse is supported.

See https://github.com/101companies/101simplejava/blob/master/README.md

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