My question concerns where this handle comes from. Isn't the handle coming from the output of 'open'? Since 'open' is the "outer" function of the 'do' construct, then why doesn't the outer function in the first example also supply its output as input to its inner function?
On Sunday, April 27, 2014 8:40:27 PM UTC-7, Amit Murthy wrote: > > Without using a do-block, you would need to pass in a function as the > first argument to 'map'. > 'open' has a variant where the first argument is again a function that > accepts an open handle. > > The do-block syntax in this case just allows you to define the said > function. > > > On Mon, Apr 28, 2014 at 8:55 AM, Peter Simon <psimo...@gmail.com<javascript:> > > wrote: > >> In the Julia manual, the second example in >> block-syntax-for-function-arguments<http://docs.julialang.org/en/latest/manual/functions/#block-syntax-for-function-arguments> >> contains >> the following do block: >> >> open("outfile", "w") do f >> write(f, data) >> end >> >> and the documentation states that "The function argument to open receives a >> handle to the opened file." I conclude from this that the return value >> (i.e., the file handle) of the open function is passed to this function f -> >> write(f, data) that is used as the first argument of open. So far, so good >> (I think). But now I go back and take another look at the first do block >> example: >> >> map([A, B, C]) do x >> if x < 0 && iseven(x) >> return 0 >> elseif x == 0 >> return 1 >> else >> return x >> endend >> >> I try to interpret this example in light of what I learned from the second >> example. The map function has a return value, consisting of the array [A, >> B, C], modified by applying the function in the do block to each element. >> If this example behaved like in the second example, then the output of the >> map function should be passed as an input to the function defined in the do >> block. Clearly this doesn't happen, so the lesson I learned from the second >> example doesn't apply here, apparently. Why not? Under what conditions is >> the output of the outer function passed as an input to the inner function? >> >> I must be looking at this wrong and would appreciate some help in getting my >> mind right :-). >> >> Thanks, >> >> Peter >> >> >
