Spending Time in Lua

ArtLeeApps

Hi all,

Can i ask a Lua question please.

I've been reading a book on Lua, and have gone back to this page several times, as it confuses me.

function derivative(f,delta) delta=delta or 1e-4 return function(x) return ( f(x + delta ) -f(x))/delta end end   ----- It Runs like this ------------   c=derivative(math.sin) print(math.cos(10),c(10)) -->-0.83907152907645-0.83904432662041 Becausefunctionsarefirst-classvaluesinLua,wecanstorethemnoto

My Question :

The part "return function(x) ....."
where is the value of "x" coming from ?
i would expect a value of "x" to be passed to the function....

TheOddLinguist

The entire function

function(x) return ( f(x + delta ) -f(x))/delta end

is the return value in this case. So,

c

is being set to a version of that function using

math.sin

as a base. Notice that in the print call, you're calling

c(10)

. So, that 10 is essentially the x for that specific instance of the function. Hope that clears it up a bit. If not, someone will come by with a better explanation. hehe

ArtLeeApps

@TheOddLinguist Thank you, that is a bit clearer yes.

its like defining a function
myfunc = math.sin(x)
and calling
myfunc(100)

which is the same as math.sin(100)

but its putting the entire user defined function .... into "c"

...i knew i should have been a brick layer....