In JavaScript, "10" + 5 is "105", and in Python it is an error. In Raku it is 15, because + always adds.
In JavaScript and Python, + has two jobs: it adds numbers and it joins strings. In Raku it has one.
In JavaScript
console.log("10" + 5);
console.log("10" + "5");
console.log("10" - 5);105 105 5
JavaScript sees a string, so + joins. - has only one job, so it subtracts.
In Python
try:
print("10" + 5)
except TypeError as e:
print("TypeError:", e)TypeError: can only concatenate str (not "int") to str
In Raku
say "10" + 5; say "10" + "5";
15 15
Both lines add. The strings are turned into numbers first.
If a string does not look like a number, there is nothing to add, and the program stops:
say "10" + "five";
Cannot convert string to number: base-10 number must begin with valid digits or '.'
Why
In Raku, the operator decides what kind of operation happens, not the values. + is always addition: it turns both sides into numbers. ~ is always joining: it turns both sides into strings.
So you can tell from the operator alone what a line will do, without knowing where the values came from. That matters, because values that come from a file or from the keyboard are always strings, and + still adds them.
Say it in Raku
To join, use ~:
say "10" ~ 5; say 10 ~ 5; say "10" + 5;
105 105 15
~ joins even two numbers: 10 ~ 5 is the string 105.