How do I make two rules with equal precedence. The obvious example is
true||false&&false
should return false because the true||false is evaluated first, then
&&false.
but also
true&&false||true
should return true because true&&false is false, but then the ||true is
evaluated.
[email protected] wrote:
[Note: parts of this message were removed to make it a legal post.]
How do I make two rules with equal precedence. The obvious example is
true||false&&false
should return false because the true||false is evaluated first, then &&false.
but also
true&&false||true
should return true because true&&false is false, but then the ||true is evaluated.
I don’t understand how your example relates to the way you worded your
question,
but if you have two or more operators at the same level of precedence,
just use
a sequence. For example, a sum of 1 or more terms can be expressed as:
rule sum
term ( (‘+’/‘-’) term )*
end
(with white-space skipping stripped out). If you want to evaluate the
result,
say by providing and calling a value() method, here’s the idiom I use:
rule add_op
‘+’ { def operate(a, b); a+b; end }
/ ‘-’ { def operate(a, b); a-b; end }
end
rule sum
term seq:(add_op term)* {
def value
seq.inject(term.value) { |s, e| e.add_op.operate(s,
e.term.value) }
end
}
end
A working example of this is in my Treetop presentation, available as
audio,
slides, and example programs, at my blog,
http://dataconstellation.com/blog.
Clifford H., Data Constellation.