Gotchas: Difference between revisions
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Here, we are adding to lists and then (after the first sentence) summing the result. But as you can see in the last sentence, summing the individual numbers by themselves doesn't accomplish anything useful.
=={{header|jq}}==
jq supports multi-arity functions, e.g. `def f(a; b):` would be the preamble for `f/2`, a two-argument version of `f`; an invocation of such a function would also use a semi-colon, e.g. `f(1; 2)`. In other programming languages, commas rather than semi-colons would be used as argument separators.
The "gotcha" here is that even if `f` has been defined as a two-argument function, the expression `f(a,b)` would be valid if `f/1` were also defined. To add to the potential for confusion, `f(1,2)` might or might not be equivalent to `f(1), f(2)`, depending on how `f/1` has been defined. Sometimes, therefore, the inadvertent use of a comma instead of a semi-colon in the invocation of a function can result in difficult-to-diagnose problems.
As with most such problems involving jq programs, the `debug` filter is likely to be helpful.
One way to avoid falling into the trap in the first place is to spend some time understanding how the invocation `f(1,2)` might NOT be equivalent to `f(1),f(2)`. (Hint: `def(s): reduce s as $x (0; .+1);`)
=={{header|Julia}}==
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