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Error in evaluation of function default arguments #649
Description
x = []
for i in range(5):
x.append(lambda i=i: print(i))
for c in x:
c()python output:
0
1
2
3
4
javascript output:
undefined
undefined
undefined
undefined
undefined
The problem is transcrypt postpones evaluation of default arguments to inside function:
export var x = [];
for (var i = 0; i < 5; i++) {
x.append ((function __lambda__ (i) {
if (typeof i == 'undefined' || (i != null && i.hasOwnProperty ("__kwargtrans__"))) {;
var i = i;
};
return print (i);
}));
}
for (var c of x) {
c ();
}To fix it we need to wrap function declaration in another closure and have default values locked inside that function call like this:
export var x = [];
for (var i = 0; i < 5; i++) {
x.append (
(function() {
var default_i = i;
return (function __lambda__ (i) {
if (typeof i == 'undefined' || (i != null && i.hasOwnProperty ("__kwargtrans__"))) {
var i = default_i;
};
return print (i);
});
})()
);
}
for (var c of x) {
c ();
}
Activity
faerot commentedon Jul 3, 2019
Ok, looks like it was already reviewed 3 years ago here:
#36
and it was suggested to consider it a transcrypt "limitation", but what about my suggested solution above? This requires minimal overhead but should provide correct behavior with python.
JdeH commentedon Aug 14, 2019
I find the current limitation very annoying and will take a good look at your solution!
trenta3 commentedon Jul 16, 2021
Is there any update on this issue?
This basically prevents using partially evaluated functions to pass around as values.
In my usage this is pretty worrysome!