FsLexYacc with WebSharper

FsLexYacc is a lexer+parser code generator from fsy and fsl files. The the official FsYacc Overview and FsLex Overview. Also see the JSON parser example for getting to know the definition languages used.

If you start from a WebSharper project, to enable the FsLexYacc code generation, add the FsLexYacc version 11.2.0 nuget package to your project. This will automatically add the build targets. Also include in your project file:

    <FsYacc Include="Parser.fsy">
      <OtherFlags>--module Parser</OtherFlags>
    </FsYacc>
    <FsLex Include="Lexer.fsl">
      <OtherFlags>--module Lexer --unicode</OtherFlags>
    </FsLex>
    <Compile Include="Parser.fsi" />
    <Compile Include="Parser.fs" />
    <Compile Include="Lexer.fs" />

(Note: Lexer.fsi seems to be producing incomplete output)

Create Parser.fsy and Lexer.fsl files to implement, the rest will be generated.

Enabling the lexer+parser for client-side use

To also use the generated code from JavaScript-enabled code, add the WebSharper.FsLexYacc nuget package too. It currently supports FsLexYacc version 11.2.0 exactly. The only remaining piece is to mark the Parser.fs and Lexer.fs files for JavaScript translation. Because these are generated files, they should not be modified as those changes would be lost. The solution that WebSharper provides is to mark files for compilation either through wsconfig.json with:

  "javascript": [ "Parser.fs", "Lexer.fs" ]

or by assembly-level attributes:

[<assembly: JavaScript("Parser.fs")>]
[<assembly: JavaScript("Lexer.fs")>]
do()

After this, you will be able to use your lexer+parser e.g.:

open FSharp.Text.Lexing
 
let lexbuf = LexBuffer<char>.FromString text
let parsed = Parser.start Lexer.tokenstream lexbuf