Help in Defining Access methods for nodes in treetop
Swapna
I am new to treetop parser. I was looking for an asm parser for which
i have a well defined grammar. I wrote the grammar and the parser is
able to parse through all the intructions. But I am having issues
while writing methods for these rules. An example code is provided
below.
rule Expression
Instruction / comment
{
def to_array
return self.elements.to_array
end
}
end
rule Instruction
Unary / Tri / Binary
{
def to_array
return self.elements.map {|e| e.to_array}
end
}
end
rule Unary
UnaryInst space?
def_to_array
self.elements[0].to_array # I get an error here saying
self.elements is nil. But my parser successfully parses the
instruction. I am unable to call the function beyond this point.
end
end
rule UnaryInst
UnaryOp sat?
{
def to_array()
return 1
end
}
end
Looks like something basic. Thanks in advance for the help.
Swapna
rule assignment
identifier '=' number {
def ast ()
Operation.new(:assignment, identifier.ast, number.ast)
end
}
end
rule identifier
[a-zA-Z_] [a-zA-Z0-9_]* { def ast () Identifier.new(text_value)
end }
end
What I tried was following
rule Instruction
Unary / Tri / Binary
{
def to_array
return self.elements.map {|e| e.to_array}
end
}
end
rule Unary
UnaryInst space?
def to_array
UnaryInst.to_array # I am unable to call this function here. I
cann access it through self.elements[0].to_array. how to i access
methods of particular rules directly?
end
}
end
rule UnaryInst
UnaryOp space?
{
def to_array
return 1
end
}
end
even in I access UnaryInst.to_array using self.elements[0].to-array. i
would like to call UnaryOp.to_array in the next step. What i see is an
error : uninitialized constant ASM::UnaryInst1::UnaryOp (NameError)
Clifford Heath
> I am having issues while writing methods for these rules. An example code is provided
> below.
>
> rule Expression
> Instruction / comment
> {
This block only applies to comment, not to Instruction. Use parentheses around (Instruction/comment) to make it apply to both.
> def to_array
> return self.elements.to_array
You don't need to say "self".
"elements" is already an array. Did you mean "elements.map{|e| e.to_array}"?
> end
> }
> end
>
> rule Instruction
> Unary / Tri / Binary
Use parentheses.
> {
> def to_array
> return self.elements.map {|e| e.to_array}
> end
> }
>
> end
>
> rule Unary
> UnaryInst space?
>
> def_to_array
> self.elements[0].to_array # I get an error here saying
> self.elements is nil. But my parser successfully parses the
> instruction. I am unable to call the function beyond this point.
I don't understand that. elements[1] might be nil, because it's optional, but not elements[0].
Normally you should use the element names (or tags) to access the elements, so instead of saying "elements[0]" you can just say "UnaryInst".
Try these things and report back.
Clifford Heath.
> end
> end
>
> rule UnaryInst
> UnaryOp sat?
> {
> def to_array()
> return 1
> end
> }
> end
>
>
> Looks like something basic. Thanks in advance for the help.
>
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Swapna Raj
Clifford Heath
> Anyways, those issues are resolved now. UnaryOp was a set of terminals which I had defines as "abc"/"cde"/"efg"...
> The issue got resolved when I changed this to ("abc"/"cde"/"efg"...). Now I am able to use UnaryOp.to_array. Not sure how this matters, since we are defining the method inside {..}
rule
A / B / C { def foo; …; end }
end
defines foo only for the C path. You can even do this:
rule
(A / B / C { def foo; …; end }) { def bar; …; end}
end
which defines foo for C, but bar for all paths. Note that
the two modules will be mixed in to the same SyntaxNode
in this case.
> Another issue I had was in accessing methods for optional non-terminals.
This is a known trap. The accessor method for C is defined
only if the rule was matched. I think this is a bug; the method
should be defined regardless, but return nil if C was not
matched. You can work around it using labels and .empty?,
because the label is always defined.
A fix for this would be welcome, if anyone has time.
Clifford Heath.