parse("...codez...") can be helpful too.
For (1) & (2), the single-quoted numbers are interpreted as literals rather
than symbols. It is possible to create a Symbol called `:1` with
`symbol("1")`, if needed, but that seems strange. The entry syntax `:1`
might be disallowed for efficiency and disambiguation - I'm not sure.
For (3), in general, a TopNode tells the compiler to resolve any names to
the current base module. It might be illustrative to look at the difference
between these expressions:
julia> a = 1
1
julia> :($a + 1)
:(1 + 1)
julia> :(1+:(a+2))
:(1 + :(a + 2))
julia> :(1+:($a+2))
:(1 + top(Expr)(:call,:+,a,2))
The last case asks for an interpolation which cannot be expanded at parse
time, because the interpolation is quoted. The `top(Expr)` and `call` are
generated to guarantee that `foo` - whatever the value of `foo` ends up as
in the Top module namespace - is used when the expression is evaluated.
(as an aside, eval'ing those last two examples will give errors, because it
is not possible to add an Int and an Expr)
On Fri, May 23, 2014 at 3:53 PM, Adam Smith
<[email protected]>wrote:
> I find it quite helpful to use dump() on expressions to see the first few
> levels of the parsed AST. That makes it easier to see what Julia is doing
> with your expressions.
>
>
> On Thursday, May 22, 2014 5:17:13 PM UTC-4, Andrew McKinlay wrote:
>>
>> I have been trying to grok Julia macros, so I've dived into the
>> metaprogramming docs. Whilst playing around with the interpreter, I've run
>> into some peculiarities that I don't quite understand.
>>
>> julia> versioninfo()
>> Julia Version 0.3.0-prerelease+2690
>> Commit e4c2f68* (2014-04-20 12:15 UTC)
>> ...
>>
>>
>> 1. Why is typeof( :(:(1+2)) ) == Expr, but typeof( :(:(1)) ) ==
>> QuoteNode?
>> 2. Why is typeof( :(1) ) == Int64, but again typeof( :(:(1)) ) ==
>> QuoteNode?
>> 3. Why is typeof( :(1+:($1+2)).args[3].args[1] ) == TopNode?
>>
>>
>> I was assuming that quoting was just a shorthand way for constructing
>> expressions, since the docs say:
>>
>>> There is special syntax for “quoting” code (analogous to quoting
>>> strings) that makes it easy to create expression objects without explicitly
>>> constructing Expr objects.
>>
>> But the types of objects constructed by quoting do not always take the
>> form of an Expr, as above.
>>
>> What is going on here?
>>
>
