understanding nearley with moo resulting datastructure - parsing

Question

I have this grammar:
let lexer = moo.compile({
comment: { match: /[\/\/.*?$|][^\n]+/, value: (s:string) => s.slice(1).trim() },
newline: { match: /[\n]+/, lineBreaks: true }
});
%}
#lexer lexer
main ->
element
| main %newline element
element -> comment
comment -> %comment
Now when I feed nearley the following input: //\n//\n//\n//\n// I get this result:
[
[
[
[
[
[
[
[
{
"type": "comment",
"value": "/",
"text": "//",
"offset": 0,
"lineBreaks": 0,
"line": 1,
"col": 1
}
]
]
],
{
"type": "newline",
"value": "\n",
"text": "\n",
"offset": 2,
"lineBreaks": 1,
"line": 1,
"col": 3
},
[
[
{
"type": "comment",
"value": "/",
"text": "//",
"offset": 3,
"lineBreaks": 0,
"line": 2,
"col": 1
}
]
]
],
{
"type": "newline",
"value": "\n",
"text": "\n",
"offset": 5,
"lineBreaks": 1,
"line": 2,
"col": 3
},
[
[
{
"type": "comment",
"value": "/",
"text": "//",
"offset": 6,
"lineBreaks": 0,
"line": 3,
"col": 1
}
]
]
],
{
"type": "newline",
"value": "\n",
"text": "\n",
"offset": 8,
"lineBreaks": 1,
"line": 3,
"col": 3
},
[
[
{
"type": "comment",
"value": "/",
"text": "//",
"offset": 9,
"lineBreaks": 0,
"line": 4,
"col": 1
}
]
]
],
{
"type": "newline",
"value": "\n",
"text": "\n",
"offset": 11,
"lineBreaks": 1,
"line": 4,
"col": 3
},
[
[
{
"type": "comment",
"value": "/",
"text": "//",
"offset": 12,
"lineBreaks": 0,
"line": 5,
"col": 1
}
]
]
]
]
I dont quite understand why the resulting array is so deeply nested and if theres a way to just have it flat for each elements. Like comments on the same semantic level should be part of one array and not nested.

Answer 1

Okay, so it turns out you have to pass a post-processor to each rule if you don't want them nested in arrays.
For instance like this:
main ->
element {% d => ({ type: "main_element", data: d[0]}) %}
| main %newline element {% d => ({ type: "main_element", data: d[2], main_data: d[0]}) %}
element -> %comment
{% d => ({ type: "element", data: d[0]}) %}
This will result in a flat structure as expected:
[
{
"type": "main_element",
"data": {
"type": "element",
"data": {
"type": "comment",
"value": "/",
"text": "//",
"offset": 12,
"lineBreaks": 0,
"line": 5,
"col": 1
}
},
"main_data": {
"type": "main_element",
"data": {
"type": "element",
"data": {
"type": "comment",
"value": "/",
"text": "//",
"offset": 9,
"lineBreaks": 0,
"line": 4,
"col": 1
}
},
"main_data": {
"type": "main_element",
"data": {
"type": "element",
"data": {
"type": "comment",
"value": "/",
"text": "//",
"offset": 6,
"lineBreaks": 0,
"line": 3,
"col": 1
}
},
"main_data": {
"type": "main_element",
"data": {
"type": "element",
"data": {
"type": "comment",
"value": "/",
"text": "//",
"offset": 3,
"lineBreaks": 0,
"line": 2,
"col": 1
}
},
"main_data": {
"type": "main_element",
"data": {
"type": "element",
"data": {
"type": "comment",
"value": "/",
"text": "//",
"offset": 0,
"lineBreaks": 0,
"line": 1,
"col": 1
}
}
}
}
}
}
}
]