How to use same token in multiple expressions?

[riej]

I'm trying to implement custom language plugin (Linden Script Language) for IntelliJ IDE. I already implemented parsing using YACC before, but have a problem while trying to do the same using GrammarKit.

The language has XYZ vector type, you can create vector using such construction:

<X, Y, Z>
<1.0, 2.0, 3.0>

But this construction is also valid:

<1, 2 < 3 > 4, 5> // same as <1, (2 < 3 > 4), 5>

But I don't know how to specify such syntax using GrammarKit. Here's short BNF file for example:

{
  parserClass="org.example.SomeParser"

  extends="com.intellij.extapi.psi.ASTWrapperPsiElement"

  psiClassPrefix="Some"
  psiImplClassSuffix="Impl"
  psiPackage="org.example.psi"
  psiImplPackage="org.example.psi.impl"

  elementTypeHolderClass="org.example.psi.SomeTypes"
  elementTypeClass="org.example.psi.SomeElementType"
  tokenTypeClass="org.example.psi.SomeTokenType"

  generateTokenAccessors=true

  tokens=[
    INTEGER = 'regexp:[+-]?[0-9]+'
    FLOAT = 'regexp:[+-]?([0-9]*\.[0-9]+|[0-9]+\.[0-9]*|[0-9]+)([Ee][+-]?[0-9]+)?[Ff]?'

    IDENTIFIER = 'regexp:[a-zA-Z_][a-zA-Z0-9_]*'

    space='regexp:\s+'
    comment='regexp://.*'
    id='regexp:\p{Alpha}\w*'
  ]
}

SomeFile ::= Statement*

Statement ::= (
    StatementVariableDeclaration
    | StatementIf
    | StatementAssign
)

StatementVariableDeclaration ::= TypeName IDENTIFIER ('=' Expression)? ';' {pin=1 recoverWhile=StatementRecover extends=Statement}
StatementIf ::= 'if' '(' Expression ')' Statement {pin=1 recoverWhile=StatementRecover extends=Statement}
StatementAssign ::= LValue '=' Expression ';' {recoverWhile=StatementRecover extends=Statement}

private StatementRecover ::= !(TypeName | 'if' | IDENTIFIER)

Expression ::= (
    ConstantValue
    | LValue
    | ExpressionPlus
    | ExpressionMinus
    | ExpressionGreater
    | ExpressionLesser
    | ExpressionVector
    | ExpressionParentheses
)

ExpressionVector ::= '<' Expression ',' Expression ',' Expression '>' {pin=1 extends=Expression}
ExpressionPlus ::= Expression '+' Expression {pin=2 extends=Expression}
ExpressionMinus ::= Expression '-' Expression {pin=2 extends=Expression}
ExpressionGreater ::= Expression '>' Expression {pin=2 extends=Expression}
ExpressionLesser ::= Expression '<' Expression {pin=2 extends=Expression}
ExpressionParentheses ::= '(' Expression ')' {pin=1 extends=Expression}

LValue ::= IDENTIFIER ('.' IDENTIFIER)? {extends=Expression}
ConstantValue ::= (INTEGER | FLOAT) {extends=Expression}

TypeName ::= 'vector'

Everything works fine like that:

vector a = <1, 2, 3>;
if (a.x > a.y) a.z = a.x;
vector d = <1, (2 > 3 < 4), 5>;

But shows errors in such case, without parentheses:

vector a = <1, 2, 3>;
if (a.x > a.y) a.z = a.x;
vector d = <1, 2 > 3 < 4, 5>;

Can someone help me please and tell how to make it work?