syntax.Expressions.txt

expr ::= 
    term 
    | '(' expr ')' 
    | UnOp expr 
    | expr BinOp expr 
    | expr '.' Field
    | expr '[' field_assign ']'

field_assign ::=
    ( Field ':=' expr (',' Field ':=' expr)* )?

field_set ::=
    ( Field ':' expr (',' Field ':' expr)* )?

term ::= 
    Command ('{' expr '}')*
    | '[' field_assign ']'
    | '[' field_set ']'
    | Quantifier '{' ids '}' '{' expr? '}' '{' expr '}'
    | '\cast' '{' expr '}' '{' type '}'
    | Var
    | Number

type ::= ...

ids ::= Ident ( ',' Ident )*

tokens:
    UnOp
    BinOp
    Field
    Var
    Ident
    Number
    Command