PEG.js help - optional free text followed by key value pairs - regex

Question

I wrote the following parser (paste into http://pegjs.org/online and it works):
Expression = Pairs / FullTextWithPairs
Pairs = (';'? _ p:Pair { return p; })*
FullTextWithPairs = fto:FullText po:Pairs
{
var arr = [];
if (fto) {
arr.push(fto);
}
return arr.concat(po);
}
FullText = ft:ValueString ';'
{
return {'key' : 'fullText', 'op': '=', 'value': ft};
}
Pair = k:Field op:Operator v:ValueString
{
var res = {'key' : k, 'op': op, 'value': v};
console.log(res);
return res;
}
Operator = ('<>' / [=><])
ValueString = vs:[^;]+ {return vs.join('');}
Field = 'location' / 'application' / 'count'
_ = ' '*
It parses this string of key-value pairs: location=USA; application<>app; count>5
to this:
[
{
"key": "location",
"op": "=",
"value": "USA"
},
{
"key": "application",
"op": "<>",
"value": "app"
},
{
"key": "count",
"op": ">",
"value": "5"
}
]
The problem is I want to enable a free-text search as well, which is entered before the key-value pairs, for example:
this: free text foobar; location=USA; application<>app; count>5
and get this:
[
{
"key": "fullText",
"op": "=",
"value": "free text foobar"
},
{
"key": "location",
"op": "=",
"value": "USA"
},
{
"key": "application",
"op": "<>",
"value": "app"
},
{
"key": "count",
"op": ">",
"value": "5"
}
]
The parser should recognize that the first part is not a key-value pair (according to "Pair" rule) and insert it as "fullText" object.
Basically "Expression" rule should do it, according to what I read in the docs - A / B means if A doesn't pass the B is tried. In the second case "Paris" is faild because "free text foobar" doesn't pass the Pairs rule, but it just throws an exception instead of moving on.
Congrats to whomever survived up to here, what am I doing wrong? :)
Thank you

Answer 1

Played with the grammar some more, the solution was to use !Pair and (for some reason) to change the order of the "Expression" rule:
Expression = FullTextWithPairs / Pairs
Pairs = (';'? _ p:Pair { return p; })*
FullTextWithPairs = fto:FullText po:Pairs
{
var arr = [];
if (fto) {
arr.push(fto);
}
return arr.concat(po);
}
FullText = !Pair ft:ValueString ';'
{
return {'key' : 'fullText', 'op': '=', 'value': ft};
}
Pair = _? k:Field op:Operator v:ValueString
{
var res = {'key' : k, 'op': op, 'value': v};
console.log(res);
return res;
}
Operator = ('<>' / [=><])
ValueString = vs:[^;]+ {return vs.join('');}
Field = 'location' / 'application' / 'count'
_ = ' '*