How I can use nested define unique argument?
define(`Honestly',`$1, define(`Does',`Iam$1')Does(Honest), $2')dnl
Honestly(Before, After)
actual result:
Before, IamBefore, After
Expected result:
Before, IamHonest, After
How Achieve the expected result ?
Break up the $1 token:
define(`Honestly',`$1, define(`Does',`Iam$'`1')Does(Honest), $2')dnl
Honestly(Before, After)
Remove the ticks around define:
define(`Honestly',$1-define(`Does',`Iam$1')Does(Honest)-$2)dnl
Honestly(Before, After)
Related
function check(str,arg;type=DataType,max=nothing,min=nothing,description="")
#argcheck typeof(arg)==type
#argcheck arg>min
#argcheck arg<max
#argcheck typeof(description)==String
return arg
end
function constr(name,arg,field)
return :(function $name($arg,$field)
new(check($name,$arg,$field))
end)
end
macro creatStruct(name,arg)
code = Base.remove_linenums!(quote
struct $name
end
end)
print(arg)
append!(code.args[1].args[3].args,[constr(name,arg.args[1].args[1],arg.args[1].args[2])])
code
end
macro myStruct(name,arg)
#creatStruct name arg
end
#myStruct test12 (
(arg1,(max=10))
)
In my code above I'm trying to build a macro that Creates a struct, and within the struct, you can define an argument with boundaries (max, min) and description, etc.
I'm getting this error:
syntax: "#141#max = 10" is not a valid function argument name
and every time I'm trying to solve it, I get another error like:
LoadError: syntax: "struct" expression not at top level
So, I think my Code/Approach is not that cohesive. Anybody can suggest tips and/or another Approche.
You're attempting to make an argument name max with a default value of 10. The error is about max=10 not being a valid name (Symbol), while max is. The bigger issue is you're trying to put this in the struct expression instead of a constructor method:
struct Foo
bar::Float64
max::Int64
end
# constructor
Foo(bar, max=10) = Foo(bar, max)
So you have to figure out how to make an expression for a method with default values, too.
Your second error means that structs must be defined in the top-level. "Top-level" is like global scope but stricter in some contexts; I don't know the exact difference, but it definitely excludes local scopes (macro, function, etc). It looks like the issue is the expression returned by creatStruct being evaluated as code in myStruct, but the LoadError I'm getting has a different message. In any case, the error goes away if I make sure things stay as expressions:
macro myStruct(name,arg)
:(#creatStruct $name $arg)
end
Given functions:
f:{[par1; par2]
:123;};
f_wrapper:{[par1; par2]
:.[{f[x, y]};(par1;par2);456];};
I am running:
f[1;2]
f_wrapper[1;2]
The first call returns 123 as expected. From the second call I am only getting a projection without f function being executed. I am expecting to receive 123 from the
There's a typo in f_wrapper. It should be:
f_wrapper:{[par1; par2]
:.[{f[x;y]};(par1;par2);456];};
You don't need to explitly pass the params as you are doing. Also the semi colon and the return at the end of you functions are overkill. Something like this works and is easier to read:
f:{[par1; par2]123};
f_wrapper:{[par1; par2]
.[f;(par1;par2);456]}
I am wondering how to get help on a Julia macro or at least find the sourcefile where it is defined. For example, I know there is a macro #spawnat.
But if I try doing
> julia> help( #spawnat )
ErrorException("wrong number of arguments")
or
> help( spawnat )
ErrorException("spawnat not defined")
Which is not great...
Put it in quotation marks:
julia> help("#spawnat")
gives
Base.#spawnat()
Accepts two arguments, "p" and an expression, and runs the
expression asynchronously on processor "p", returning a
"RemoteRef" to the result.
You can get help on the help function with help(help).
In most OO languages, where variables may point to objects, they may also have a null value, which is highly convenient.
In Matlab, I have a function which parses a command, and then returns a cell array, or false (which is equal to zero — which is another common pattern) if it fails:
function re = parse(s)
...
if (invalid)
re = false;
return;
end
end
The problem is that when I check the result, it gives an error:
re = parse(s);
if (false == re)
Undefined function 'eq' for input arguments of type 'cell'.
I've written a function to check it without an error: strcmp('logical', class(re)) && false == re, but that seems to be really slow for use in hot areas of the code, and also inconvenient if I have to add this function to every M file I'm writing.
Using NaN is even worse, because besides throwing that error, it also isn't equal to itself.
What's a better alternative for use with this pattern?
You can use the isequal function to compare any two items without causing that error. For example:
if isequal (re, false)
%code here
end
A good alternative is to use the empty array: [] and isempty(re) to check. This doesn't throw the error.
Reference: http://www.mathworks.com.au/matlabcentral/newsreader/view_thread/148764
If you can change the function parse one solution would be to return two output arguments [re status] = parse(s), where status would be logical variable. Set it to true in case of success, and to false otherwise.
I would use the empty cell array {} if it is not a valid result otherwise. Using empty matrices is MATLAB standard (see Evgeni Sergeev's answer), but using an empty cell array instead of an empty numeric array ensures that you'll always end up with the same type of result.
If, on the other hand, the empty cell array {} is a valid result of your function, then I'd use an exception to signalize a problem:
if invalid
error('Parse:InvalidArgumentError', 'The input is invalid.');
end
Make sure to use an appropriate error ID (first argument to error) so that you can catch exactly that exception when you call the function:
try:
result = parse(something);
catch ME
if strcmp(ME.identifier, 'Parse:InvalidArgumentError')
fprintf('Ooops\n');
else
% Some other error
ME.rethrow();
end
end
I think the problem is that matlab functions don't return pointers but copies of values.
IMHO the best best approach would be to define your own "pointer" class. Inside you can define an "isNull()" command or even override comparison to produce the behavior you desire.
On compiling the following code with Scala 2.7.3,
package spoj
object Prime1 {
def main(args: Array[String]) {
def isPrime(n: Int) = (n != 1) && (2 to n/2 forall (n % _ != 0))
val read = new java.util.Scanner(System.in)
var nTests = read nextInt // [*]
while(nTests > 0) {
val (start, end) = (read nextInt, read nextInt)
start to end filter(isPrime(_)) foreach println
println
nTests -= 1
}
}
}
I get the following compile time error :
PRIME1.scala:8: error: illegal start of simple expression
while(nTests > 0) {
^
PRIME1.scala:14: error: block must end in result expression, not in definition
}
^
two errors found
When I add a semicolon at the end of the line commented as [*], the program compiles fine. Can anyone please explain why does Scala's semicolon inference fail to work on that particular line?
Is it because scala is assuming that you are using the syntax a foo b (equivalent to a.foo(b)) in your call to readInt. That is, it assumes that the while loop is the argument to readInt (recall that every expression has a type) and hence the last statement is a declaration:
var ntests = read nextInt x
wherex is your while block.
I must say that, as a point of preference, I've now returned to using the usual a.foo(b) syntax over a foo b unless specifically working with a DSL which was designed with that use in mind (like actors' a ! b). It makes things much clearer in general and you don't get bitten by weird stuff like this!
Additional comment to the answer by oxbow_lakes...
var ntests = read nextInt()
Should fix things for you as an alternative to the semicolon
To add a little more about the semicolon inference, Scala actually does this in two stages. First it infers a special token called nl by the language spec. The parser allows nl to be used as a statement separator, as well as semicolons. However, nl is also permitted in a few other places by the grammar. In particular, a single nl is allowed after infix operators when the first token on the next line can start an expression -- and while can start an expression, which is why it interprets it that way. Unfortunately, although while can start a expression, a while statement cannot be used in an infix expression, hence the error. Personally, it seems a rather quirky way for the parser to work, but there's quite plausibly a sane rationale behind it for all I know!
As yet another option to the others suggested, putting a blank newline between your [*] line and the while line will also fix the problem, because only a single nl is permitted after infix operators, so multiple nls forces a different interpretation by the parser.