Creating my first semantic: Missing semantic action for '_iter' in operation 'eval'.

[treimers]

Guys,

this is awesome what you create here, many thanks first of all to you!

I am totally new to lexing, parsing and Ohm but at least I managed to create my first grammar. Maybe its not perfect but I was able to create a grammar for ER diagrams with Entities and References like

Entity Sales as S {
       sold_date date
       product_id int
       amount int
}
Entity Product as P {
       id int [pk]
       name string
       Product string
}
Entity Region as R
Ref Sales > Region

Now I could parse some test input and get the expected results.

Model {
	Statements
	  = Statement*
	Statement (valid statement starting with Entity or Ref)
		= "Entity" ident ("as" ident)? Attributes*  -- entityDeclaration
		| "Ref" Refelement                          -- refDeclaration
	Refelement (valid Ref element with "entity > entity" or "entity.attribute > entity.attribute")
		= ident "." ident ">" ident "." ident       -- rowRef
		| ident ">" ident                           -- tableRef
	Attributes
        = "{" Attribute* "}" 
	Attribute
		= ident (datatype)? ("[pk]")?
	datatype
		= "date"
		| "double"
		| "int"
		| "string"
	ident  (an identifier)
		= letter (alnum | "_")*
	// the two types of comments
	comment = multiLineComment | singleLineComment
	multiLineComment = "/*" (~"*/" any)* "*/"
	singleLineComment = "//" (~lineTerminator any)*
	// the valid line terminators (used by single line comment)
	lineTerminator = "\\n" | "\\r" | "\\u2028" | "\\u2029"
	// add our comments to white spaces known to Ohm
	space += comment
}

Now I would like to create my first semantic

		const semantics = g.createSemantics().addOperation('eval', {
			Statements(e) {
				return e.eval();
			},
			Statement(e) {
				return e.eval();
			},
			Statement_entityDeclaration(entity, ident, as, ident2, attributes) {
				return ident.eval();
			},
			Statement_refDeclaration(ref, refelement) {
				return refelement.eval();
			},
			Refelement(e) {
				return e.eval();
			},
			Refelement_rowRef(entity1, dot1, attribute1, greater, entity2, dot2, attribute2) {
				return entity1.eval();
			},
			Refelement_tableRef(entity1, greater, entity2) {
				return entity1.eval();
			},
			Attributes(open, e, close) {
				return e.eval();
			},
			Attribute(e, type, pk) {
				return e.eval();
			},
			datatype(e) {
				return e.eval();
			},
			ident(letter, alnum) {
				return this.sourceString;
			},
		});

But it fails when I try to run it with:

ERROR
Missing semantic action for '_iter' in operation 'eval'.
NOTE: as of Ohm v16, there is no default action for iteration nodes — see
https://ohmjs.org/d/dsa for details.
Action stack (most recent call last):
eval > Statements
eval > _iter

I am pretty sure that I am mistaking with something basic but I was unable to understand the hints here

https://github.com/ohmjs/ohm/blob/main/doc/patterns-and-pitfalls.md

Can somebody please shine some light for me? Thanks in advance!

[treimers]

Ok, I managed to solve my issue accordings the this short section: https://github.com/ohmjs/ohm/blob/main/doc/api-reference.md#semantic-actions

I added these defintions to my grammar:
_iter(...children) {
return children.map(c => c.eval());
},
_terminal() {
return this.sourceString;
},

I am still in the phase of learning and will try to understand what I did and why it worked :)