command  = action [ query ] [ return ]
action   = ("/" word)+
query    = "where" expr
expr     = expr "and" expr | expr "or" expr | "not" expr | hasExpr | eqExpr | lessExpr | moreExpr | notExpr | nestedExpr
hasExpr  = name
eqExpr   = name "=" value
lessExpr = name "<" value
moreExpr = name ">" value
notExpr  = name "!=" value
nestedExpr = "(" expr ")" 
return   = "return" (name)+