I have the following functions.
foo(x) = x + 1
bar(x) = x * 2
I use them in a wrapper function (not sure whether this is even important).
function baz(x)
d = Dict{Symbol,Any}()
d[:foo] = foo(x)
d[:bar] = bar(x)
return d
end
The problem is that foo() and bar() can fail, and I want the code to continue running in this case. Introducing try catch statements would make the code very messy, however. So, is there maybe one of the following two solutions out there, that could make this easier?
Dream Solution
A macro that I could just write in front of d[:foo] = foo(x) and which in case of failure would write a default value do d[:foo].
Also-a Solution
A macro that would just continue if the code fails.
So, I managed to do the following. However, I have no clue if this is in any way good style.
macro tc(ex)
quote
try
$(esc(ex))
catch
missing
end
end
end
#tc foo(1)
1
#tc foo("a")
missing
Note the $(esc(ex)). This is important. If the expression is not escaped, the macro will work as expected in the global scope but not inside a function (as in the question). If anyone can provide a crisp explanation of why this is the case, please add a comment.
Related
I am writing a class-based test suite in MATLAB for a timeseries handling package. The first test in my suite needs to check whether a connection exists to a Haver database on a network drive. If the connection does not exist, then the first test should abort the rest of the suite using one of the fatalAssert methods.
One complicating factor, which I have excluded from the exposition below, but I will mention now is that I need to use an anonymous function to check the connection to Haver (unless someone has a better idea). My package handles data from multiple sources, Haver only being one of them.
I have a parent-class test suite that performs general tests for all of the sources. I then inherit this parent-class into specific child-class test suites and set specific parameters in their respective TestMethodSetup method. One of these parameters is an anonymous function, connfun, and a location, connloc, which I use in the parent-class to test the connection. The reason I do this is because the parent tests are executed first, so I would have to wait for all of those to end if I wanted to test the connection in the child class.
This also complicates the order of execution. If I want to assign the connfun in the child class, then I have to use either the TestMethodSetup or TestClassSetup of the child class (open to recommendations on which is best here) and put this connection test in the Test method of the parent class. I noticed the if I put checkConn in the TestMethodSetup and TestClassSetup of the parent class was running before that of the child class, I was unable to pass the anonymous function and the test would be incomplete.
Putting the previous point aside for a moment, this was my first attempt at writing the test in the parent-class (note that I used a fatalAssertEqual instead of a fatalAssertTrue because isconnection() does not return a logical):
methods (Test)
function checkConn(testCase)
connloc = 'pathToHaverDatabase';
connfun = #(x) isconnection(haver(x));
testCase.fatalAssertEqual(connfun(connloc), 1);
end
end
The above works when there is a connection, but the problem that I bumped into with this is that when I cannot access connloc, an error ocurrs during the call to haver(). So instead of returning a 1 or 0 from the isconnection() call that I can fatalAssertEqual on, all of checkConn errors out due to haver(). This then leads to the rest of the tests running (and failing, which is exactly what I want to avoid).
My next idea works for both cases, but it feels like bad code, and does not have the anonymous function specification described above.
methods (Test)
function checkConn(testCase)
connloc = 'pathToHaverDatabase';
connfun = #(x) isconnection(haver(x));
try
isconn = connfun(connloc);
catch
isconn = 0;
end
testCase.fatalAssertEqual(isconn, 1)
end
end
When I wrote this, I did not necessarily want to distinguish between not having access to the network drive, not being able to call the haver() function, and getting an isconnection equal to 0 because the last case covers all three. But I realized that if I did differentiate them, then it would be a bit more robust, but it's still missing the anonymous function taht I could pass from child to parent.
properties
connloc = 'pathToHaverDatabase';
end
methods (Test)
function checkDrive(testCase)
isfound = fillattrib(testCase.connloc);
testCase.fatalAssertTrue(isfound);
end
function checkHaver(testCase)
try
hav = haver(testCase.connloc);
ishaver = ~isempty(hav);
catch
ishaver = false;
end
testCase.fatalAssertTrue(ishaver);
end
function checkConn(testCase)
connfun = #(x) isconnection(haver(x));
testCase.fatalAssertEqual(connfun(testCase.connloc), 1);
end
end
Ideally, what I would want is a fatalAssert method (or something similar) that ends the test suite when its input is an error. Something that would perhaps be called fatalAssertNotError, but I don't think that exists. If it did, the last line of my first function would simply be testCase.fatalAssertNotError(connfun(connloc)) and I would not have to worry about all the cases.
I'm very open to dynamic rewrite of this whole test setup, so any specific comments or general advice are welcome!
First of all, I think the fatalAssert case is a strong use case to provide something like fatalAssertNotError. One reason why it is not part of the package is because many/most times people don't want to check whether something doesn't error, they just want to call the code, and if it errors, it fails for the test author automatically and it is much simpler. However, other qualification types like fatal assertions and assumptions perhaps point to the need to provide this so you can choose the outcome of the test in the presence of an error, in cases where you don't want it to fail (like with assumptions) or you want it to fail "more strongly" like with fatal assertions.
That being said, I am still not convinced that you can't achieve what you are ultimately trying to do without it. The question I have centers around why you can't use TestClassSetup. It is not clear to me exactly why you weren't able to customize in the derived test class to get the behavior you want. For example, does something like this work?
classdef BaseTest < matlab.unittest.TestCase
properties(Abstract)
connloc
connfun
end
methods(TestClassSetup)
function validateConnection(testCase)
% If this errors it behaves like an assertion (not fatal assertion)
% and fails all tests in the test class. If it doesn't error but
% doesn't return 1 then the assertion failure will occur.
testCase.assertEqual(connfun(connloc), 1,
'Could not establish a connection to the database');
end
end
end
classdef DerivedTest < BaseTest
properties
connloc = 'pathToHaverDatabase';
connfun = #(x) isconnection(haver(x));
end
methods(Test)
function testSomething(testCase)
% Have at least one test method to test it out
end
end
end
Hope that helps!
If you really want to use a function you can define a nested one like this:
methods (Test)
function checkConn(testCase)
connloc = 'pathToHaverDatabase';
function res = connfun(x)
try
res = isconnection(haver(x));
catch
res = false
end
end
testCase.fatalAssertEqual(connfun(connloc), 1);
end
end
Nested functions can be a bit confusing to me because of the way they share data with the parent function. There really is no difference between an anonymous function and a nested function.
The alternative is to put the function at the end of the file, outside the classdef block:
classdef ...
%...
methods (Test)
function checkConn(testCase)
connloc = 'pathToHaverDatabase';
function res = connfun(x)
try
res = isconnection(haver(x));
catch
res = false
end
end
testCase.fatalAssertEqual(connfun(connloc), 1);
end
end
%...
end
function res = connfun(x)
try
res = isconnection(haver(x));
catch
res = false
end
end
But I honestly don't understand why you need to have a function call within fatalAssertEqual. The code you have seems perfectly fine to me.
I would like to call a macro in a Julia package (#defNLExpr in JuMP) using an argument that is runtime dependent. The argument is an expression that depends on the runtime parameter n. The only way that I can think of doing this is something like the following:
macro macro1(x)
y=length(x.args);
return esc(:(k=$y-1))
end
macro macro2(n)
x="0";
for i=1:n
x="$x+$i"
end
x=parse(x);
return :(#macro1($x))
end
n=rand(1:3)
println(n)
if (n==1)
#macro2(1)
elseif (n==2)
#macro2(2)
elseif (n==3)
#macro2(3)
else
error("expected n in 1:3")
end
println(k)
Here I have assumed that my runtime n will always be in the range 1-3. I use macro2 to build-up all possible expressions for these different possible values of n, and call the external macro (which I have replaced by the simplified macro1 here) for each of them. The calls to macro1 are in if statements, so only the correct one (determined from the value of n at runtime) will actually be executed.
Although this seems to work, is there a more efficient way of achieving this?
Seems that you might be looking for eval? Be aware that it should be used with care though, and that it not very fast since it has to income the compiler each time it is called.
If it's a limitation to you that it evaluates the expression in global scope then, there are some ways to work around that.
Just having a little difficulty with the syntax of matlab functions;
function f = fact(x)
if x == 1
return
else
f = 1 - x*(fact(x-1))
end
end
When calling this function in the command window with the argument 10 I receive the error
Undefined function 'fact' for input arguments of type 'double'.
Error in recursion (line 6)
f = 1 - x*(fact(x-1))
I've had a look around and solutions for the first revolve around the pathing of the m-file which doesn't seem to be a problem as other files in the same directory run fine,
The second I'm not sure why the error in line 6 occurs, my guess is it has something to do with the variable and function names.
As a side question, are both these end statements necessary?
Thanks!
The most obvious error is your function filename. You have a function called fact defined in your code but you named your file recursion. Make sure that both your function name and the filename are both called fact.
If you were to name your file as recursion, then make the function name defined in your code as fact, this is what would happen if you tried calling your code:
>> f = recursion(10);
Undefined function 'fact' for input arguments of type 'double'.
Error in recursion (line 6)
f = 1 - x*(fact(x-1));
... look familiar?
As such make sure your filename and your function name are named the same. In fact, in the MATLAB editor, it should automatically give you an error saying that both of these are not the same.
There is also another error in your code. The base case is not defined properly. Always remember when you are writing recursive algorithms is that eventually the function is going to return... and that's when you hit the base case. We can see here that it is when x = 1. When x = 1, you're supposed to assign something to f which is the output. You are simply exiting the function, and so when x becomes 1, your code will spit out an error saying that f was not assigned when the function finishes. As such, you need to figure out what your base case is. I'm going to assume that your base case (when x = 1) is going to equal 0. You will obviously need to change this as I don't know what your code is actually computing. Basically, you need to do this:
function f = fact(x)
if x == 1
f = 0; %// Base case needs to change according to your specs
else
f = 1 - x*(fact(x-1))
end
end
When I do this, I get the following output when x = 10
>> f = fact(10);
f =
1334961
I don't get an error when I run this code now. Also, check to see if you have any variables named fact in your workspace. When this happens, you are in fact shadowing over your function with a variable, so it is actually trying to access the variable called fact instead. As such, try clearing your workspace by doing clear all;, then try this code again.
One warning
If you were to specify x to be 0 or negative, this function will never stop. As such, you need to provide some check and perform the proper action when this happens. Also, you need to make sure that you specify what type of inputs are accepted for x. Judging from the context, x are positive integers only. As what #Glen_b has noted, should you provide any number that isn't a positive integer, this function will never stop as x will never equal 1 down the recursion pipeline.
To answer your optional question
The first end statement is required to end the if statement. The second end statement isn't required, but it's good practice anyway. However, if you have multiple functions defined inside your function file, then yes it is most definitely required to properly signify that the end of that function is defined there. However, you don't need it if you're only writing one function per file, but I would recommend keeping it there as it's good practice.
I am attempting to use LuaJ with Scala. Most things work (actually all things work if you do them correctly!) but the simple task of setting object values has become incredibly complicated thanks to Scala's setter implementation.
Scala:
class TestObject {
var x: Int = 0
}
Lua:
function myTestFunction(testObject)
testObject.x = 3
end
If I execute the script or line containing this Lua function and pass a coerced instance of TestObject to myTestFunction this causes an error in LuaJ. LuaJ is trying to direct-write the value, and Scala requires you to go through the implicitly-defined setter (with the horrible name x_=, which is not valid Lua so even attempting to call that as a function makes your Lua not parse).
As I said, there are workarounds for this, such as defining your own setter or using the #BeanProperty markup. They just make code that should be easy to write much more complicated:
Lua:
function myTestFunction(testObject)
testObject.setX(testObject, 3)
end
Does anybody know of a way to get luaj to implicitly call the setter for such assignments? Or where I might look in the luaj source code to perhaps implement such a thing?
Thanks!
I must admit that I'm not too familiar with LuaJ, but the first thing that comes to my mind regarding your issue is to wrap the objects within proxy tables to ease interaction with the API. Depending upon what sort of needs you have, this solution may or may not be the best, but it could be a good temporary fix.
local mt = {}
function mt:__index(k)
return self.o[k] -- Define how your getters work here.
end
function mt:__newindex(k, v)
return self.o[k .. '_='](v) -- "object.k_=(v)"
end
local function proxy(o)
return setmetatable({o = o}, mt)
end
-- ...
function myTestFunction(testObject)
testObject = proxy(testObject)
testObject.x = 3
end
I believe this may be the least invasive way to solve your problem. As for modifying LuaJ's source code to better suit your needs, I had a quick look through the documentation and source code and found this, this, and this. My best guess says that line 71 of JavaInstance.java is where you'll find what you need to change, if Scala requires a different way of setting values.
f.set(m_instance, CoerceLuaToJava.coerce(value, f.getType()));
Perhaps you should use the method syntax:
testObject:setX(3)
Note the colon ':' instead of the dot '.' which can be hard to distinguish in some editors.
This has the same effect as the function call:
testObject.setX(testObject, 3)
but is more readable.
It can also be used to call static methods on classes:
luajava.bindClass("java.net.InetAddress"):getLocalHost():getHostName()
The part to the left of the ':' is evaluated once, so a statement such as
x = abc[d+e+f]:foo()
will be evaluated as if it were
local tmp = abc[d+e+f]
x = tmp.foo(tmp)
In CoffeeScript, the while loop comes standard:
while x()
y()
However, the following1 doesn't work:
do
y()
while x()
And this is simply sugar for the first example:
y() while x()
Does CoffeeScript come with a built-in loop that executes at least once?
1As an aside, do is a keyword — it's used to call anonymous functions.
The CoffeeScript documentation says:
The only low-level loop that CoffeeScript provides is the while loop.
I don't know of a built-in loop that executes at least once, so I guess the alternative is
loop
y()
break if x()
I know that this answer is very old, but since I entered here via Google, I thought someone else might as well.
To construct a do...while loop equivalent in CoffeeScript I think that this syntax emulates it the best and easiest and is very readable:
while true
# actions here
break unless # conditions here
Your guess is correct: There is no do-while equivalent in CoffeeScript. So you'd typically write
y()
y() while x()
If you find yourself doing this often, you might define a helper function:
doWhile = (func, condition) ->
func()
func() while condition()
I found this could be accomplished through a short circuit conditional:
flag = y() while not flag? or x()
I've been working on a project where I simply force the condition to evaluate at the end of the loop, then terminate at the beginning.
# set the 'do' variable to pass the first time
do = true
while do
# run your intended code
x()
# evaluate condition at the end of
# the while code block
do = condition
# continue code
It's not very elegant, but it does keep you from defining a new function just for your while code block and running it twice. There generally is a way to code around the do...while statements, but for those time that you can't you have a simple solution.