A constant is
attribute
Selections are to be written as
\sigma[predicate](relation)
And are parsed into a Selection js object. The predicate itself consists of a boolean formula that is composed by formula with ∧, ∨, or ¬. Or it is the evaluation of left θ right with left and right either constants or attributes.
θ can be one of ('==' / '!=' / '<=' / '>=' / '<' / '>') and is named predicateOp.
The attribute is referenced via the getAttr attribute.
selection = '\sigma'pred:predicate'' { return new Selection(pred, rel) } predicate = fst:predicateEl [ ]* p:predicateOp [ ]* snd:predicateEl { return Function("tuple", "return " + fst + p + snd) } predicateOp = ('==' / '!=' / '<=' / '>=' / '<' / '>') predicateEl = a:attrName { return "tuple['"+ a +"']"; } /* An attribute / / """a:[^"]+""" { return """ + a.join("") + """; } / A constant string */ / digits:[0-9]+ { return parseInt(digits.join(""), 10); }