Hime - Quickstart for C#

This guide gets you started with Hime using C#. It is also available for Java and Rust. The program here is to download the tooling, get a prepared grammar, compile it with himecc and use the generated parser.

Pre-requisites for this guide are:
  • A local installation of a compatible .Net platform such as:
    • The .Net Framework 2.0 or higher on Windows (installed by default on Windows Vista and up).
    • Mono 4.6 or higher on Linux and MacOS.
    • .Net Core 2.0 or higher on a compatible OS.

Get the tooling

The toolchain for Hime can be found on the download page.
Step 1 Download and extract the toolchain package.
You may want some editing support for Hime grammars. In this case, head to the editors line-up page. For an IDE experience, we recommend the Visual Studio Code extension.

Get the grammar

Step 2 Create and open a file named MathExp.gram.
Step 3 Then copy-paste in this file the following grammar:

grammar MathExp
{
  options
  {
    Axiom = "exp"; // the top variable for this grammar
    Separator = "SEPARATOR"; // the terminal that represent white space
  }
  terminals
  {
    WHITE_SPACE -> U+0020 | U+0009 | U+000B | U+000C ;
    SEPARATOR   -> WHITE_SPACE+;

    INTEGER     -> [1-9] [0-9]* | '0' ;
    REAL        -> INTEGER? '.' INTEGER  (('e' | 'E') ('+' | '-')? INTEGER)?
                |  INTEGER ('e' | 'E') ('+' | '-')? INTEGER ;
    NUMBER      -> INTEGER | REAL ;
  }
  rules
  {
    exp_atom   -> NUMBER
               | '(' exp ')' ;
    exp_factor -> exp_atom
               |  exp_factor '*' exp_atom
               |  exp_factor '/' exp_atom ;
    exp_term   -> exp_factor
               |  exp_term '+' exp_factor
               |  exp_term '-' exp_factor ;
    exp        -> exp_term ;
  }
}

Compile the grammar

Now that we have a grammar, let's compile it to generate the parser. The toolchain package contains at its root useful front scripts that can be to invoke the himecc compiler. On Windows, you should look for the himecc.bat script. On Linux and MacOS you should look for the himecc script. If this does not suit you, you may invoke the himecc.exe assembly for your installed framework.

Step 4 Compile the MathExp.gram:

  • On Windows: himecc.bat MathExp.gram or explicitly with net461/himecc.exe MathExp.gram
  • On Linux and MacOS: ./himecc MathExp.gram
  • On any OS, explicitly with .Net Core: dotnet netcore20/himecc.dll MathExp.gram
  • On any OS, explicitly with Mono: mono net461/himecc.exe MathExp.gram

The tool will generate 4 files:

  • MathExpLexer.cs, the source file for the lexer
  • MathExpLexer.bin, the binary representation of the lexer’s automaton
  • MathExpParser.cs, the source file for the parser
  • MathExpParser.bin, the binary representation of the parser’s automaton

Note here that the default target for himecc is the .Net platform; so that we did not had to explicitly set the target. For a complete guide to the options of himecc, head to the reference page.

Setup the test project

Step 5 Setup a test project; either as a .Net Core app, or as a .Net Framework application. Use the following project layout:

test/
+-> test.csproj
+-> Program.cs
+-> MathExpLexer.cs
+-> MathExpLexer.bin
+-> MathExpParser.cs
+-> MathExpParser.bin

Step 6 Set the minimal test.csproj:

<?xml version="1.0" encoding="utf-8"?>
<Project Sdk="Microsoft.NET.Sdk">
    <PropertyGroup>
    <SchemaVersion>2.0</SchemaVersion>
    <OutputType>Exe</OutputType>
    <RootNamespace>TestHime</RootNamespace>
    <AssemblyName>TestHime</AssemblyName>
    <!-- change this to netcoreapp2.0 for a .Net Core application -->
    <TargetFrameworks>net461</TargetFrameworks>
    <Version>1.0.0</Version>
    </PropertyGroup>
    <ItemGroup>
        <!-- so that MathExpLexer.bin MathExpParser.bin are included -->
        <EmbeddedResource Include="*.bin" />
    </ItemGroup>
    <ItemGroup>
        <!-- reference to the .Net runtime for generated parsers -->
        <PackageReference Include="Hime.Redist" Version="3.4.0"/>
    </ItemGroup>
</Project>

To use produce a .Net Code application instead of a .Net Framework or Mono application, simply replace net461 by netcoreapp2.0 in the <TargetFrameworks> tag.

Step 7 Set the minimal Program.cs:

using System;
using Hime.Redist; // the namespace for the Hime Runtime
using MathExp; // default namespace for the parser is the grammar's name

namespace TestHime
{
    class Program
    {
        public static void Main(string[] args)
        {
            // Creates the lexer and parser
            MathExpLexer lexer = new MathExpLexer("2 + 3");
            MathExpParser parser = new MathExpParser(lexer);
            // Executes the parsing
            ParseResult result = parser.Parse();
            // Prints the produced syntax tree
            Print(root, new bool[] {});
        }

        private static void Print(ASTNode node, bool[] crossings)
        {
            for (int i = 0; i < crossings.Length - 1; i++)
                Console.Write(crossings[i] ? "|   " : "    ");
            if (crossings.Length > 0)
                Console.Write("+-> ");
            Console.WriteLine(node.ToString());
            for (int i = 0; i != node.Children.Count; i++)
            {
                bool[] childCrossings = new bool[crossings.Length + 1];
                Array.Copy(crossings, childCrossings, crossings.Length);
                childCrossings[childCrossings.Length - 1] = (i < node.Children.Count - 1);
                Print(node.Children[i], childCrossings);
            }
        }
    }
}

Build and execute the test project

Step 8 Build the test project:

  • Using the .Net Framework or Mono: nuget restore
    Then: msbuild
  • Using .Net Core: dotnet restore
    Then: dotnet build

Step 9 Execute the test project:

  • Using the .Net Framework or Mono: bin/Debug/net461/TestHime.exe, or with Mono mono bin/Debug/net461/TestHime.exe
  • Using .Net Core: dotnet bin/Debug/netcoreapp2.0/TestHime.dll

The output of the program should a text printout of the produced syntax tree be as follow:

exp
+-> exp_term
    +-> exp_term
    |   +-> exp_factor
    |       +-> exp_atom
    |           +-> NUMBER = 2
    +-> + = +
    +-> exp_factor
        +-> exp_atom
            +-> NUMBER = 3

This concludes this guide. For a more complete tutorial, head over to the the first C# tutorial.