gherkin.berp

[
	Tokens -> #Empty,#Comment,#TagLine,#FeatureLine,#BackgroundLine,#ScenarioLine,#ScenarioOutlineLine,#ExamplesLine,#StepLine,#DocStringSeparator,#TableRow,#Language
	IgnoredTokens -> #Comment,#Empty
	ClassName -> Parser
	Namespace -> Gherkin
]

GherkinDocument! := Feature?
Feature! := Feature_Header Background? Scenario_Definition*
Feature_Header! := #Language? Tags? #FeatureLine Feature_Description

Background! := #BackgroundLine Background_Description Scenario_Step*

// we could avoid defining Scenario_Definition, but that would require regular look-aheads, so worse performance
Scenario_Definition! := Tags? (Scenario | ScenarioOutline)

Scenario! := #ScenarioLine Scenario_Description Scenario_Step*

ScenarioOutline! := #ScenarioOutlineLine ScenarioOutline_Description ScenarioOutline_Step* Examples_Definition*
// after the first "Examples" block, interpreting a tag line is ambiguous (tagline of next examples or of next scenario)
// because of this, we need a lookahead hint, that connects the tag line to the next examples, if there is an examples block ahead
Examples_Definition! [#Empty|#Comment|#TagLine->#ExamplesLine]:= Tags? Examples
Examples! := #ExamplesLine Examples_Description Examples_Table?
Examples_Table! := #TableRow #TableRow*

Scenario_Step := Step
ScenarioOutline_Step := Step

Step! := #StepLine Step_Arg?
Step_Arg := (DataTable | DocString)

DataTable! := #TableRow+
DocString! := #DocStringSeparator #Other* #DocStringSeparator

Tags! := #TagLine+

Feature_Description := Description_Helper
Background_Description := Description_Helper
Scenario_Description := Description_Helper
ScenarioOutline_Description := Description_Helper
Examples_Description := Description_Helper

// we need to explicitly mention comment, to avoid merging it into the description line's #Other token
// we also eat the leading empty lines, the tailing lines are not removed by the parser to avoid lookahead, this has to be done by the AST builder
Description_Helper := #Empty* Description? #Comment*
Description! := #Other+