Legivel Features

Legivel is split into two parts:

  • Legivel.Parser: parses any Yaml-1.2, into a generic native structure (representation graph)
  • Legivel.Mapper: maps the output of Legivel.Parser to specific native types.


The Legivel.Parser can parse any Yaml1.2 string to a native format - this includes any Yaml construct which may not be supported by the F# or C# languages. The yaml string may contain any number of yaml documents, as demonstrated in example 2.8.

The parser implements all recommended schema's. The (not official name) YamlExtended schema implements all tags from the Yaml Tag Repository except !!yaml.

The parser is found in Legivel.Parser, and you can invoke it with any of the given Yaml schema's, found in Legivel.TagResolution, or a customized one.

open Legivel.Parser
open Legivel.TagResolution

let YamlParse s =
    let parser = Yaml12Parser(YamlExtended.Schema)
    let repr = (parser.``l-yaml-stream`` s)

Note, even though it is trivial to inject your own schema, it is not trivial to create your own schema. Please refer to the TagResolution source code to find your example. Also read the Yaml specification here and here, as the Legivel parser follows these specifications.

The source code in the Legivel.Parser is directly related to the Yaml rules from the specification. The function name of each rule implementation has the same name as in the specification. So you can copy/paste and use a Find function in the code, or on the spec-page. All spec-examples have been implemented as a unit test.


The Legivel.Mapper takes the Legivel.Parser's output and maps it to native types, as sofar is supported. As Yaml has no contract or metadata facility, the mapper requires a target native type, which is considered as contract for the yaml conversion.

Conversion happens in a contract-first fashion; ie the mapper tries to search the input yaml for contract requirements. Any extra yaml, foreign to the contract (target type), is ignored.

The Legivel mapper supports the following F# native types, which may be nested without any limit:

  • Primitive types: int, float, bool, string
  • F# list type
  • F# record type
  • F# option type
  • F# discriminated union type
  • F# Map type

Please refer to the Tutorials, for mapping specifications.

The Legivel.Mapper has been designed with customization in mind. You can add your own yaml to native mappers, discard current mappers. You can even decide not to use this component at all.

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