this should work:  

function something(i,x,y,s,n)
type = tpt.get_property("type", x + math.random(-1,1), y + math.random(-1,1))
if type == tpt.el.watr.id then
tpt.parts[i].type = tpt.el.pste.id
end
end
tpt.element_func(something,tpt.el.clst.id)

line 3 is the first element

line 7 is the second element

and line 4 is the resulting element

also if you do it the way i just did you might want to do this: 

function something(i,x,y,s,n)
type = tpt.get_property("type", x + math.random(-1,1), y + math.random(-1,1))
if type == tpt.el.clst.id then
tpt.parts[i].type = tpt.el.pste.id
end
end
tpt.element_func(something,tpt.el.watr.id)

function something(i,x,y,s,n)
type = tpt.get_property("type", x + math.random(-1,1), y + math.random(-1,1))
if type == tpt.el.watr.id then
tpt.parts[i].type = tpt.el.pste.id
end
end
tpt.element_func(something,tpt.el.clst.id)

it makes it so not just one turns to pste but both turn to pste. 

also you can name the function, I just use the element its for due to me being bad at making names :P

function pasteReaction(i,x,y,s,n)
type = tpt.get_property("type", x + math.random(-1,1), y + math.random(-1,1))
if type == tpt.el.watr.id then
tpt.parts[i].type = tpt.el.pste.id
end
end
tpt.element_func(pasteReaction,tpt.el.clst.id)

also if you want more than 1 product

function pasteReaction(i,x,y,s,n)

chance = math.random(-1,1) --1/3 chance of a single product
type = tpt.get_property("type", x + math.random(-1,1), y + chance)
if type == tpt.el.watr.id then

if chance == 1 then
tpt.parts[i].type = tpt.el.pste.id --first product pste
end

if chance == 0 then

tpt.parts[i].type = tpt.el.acid.id --second acid

end

if chance == -1 then

tpt.parts[i].type = tpt.el.thdr.id --third thdr

end
end

end
tpt.element_func(pasteReaction,tpt.el.clst.id)

wow slow typing and look how many comments...

wow i love how you added onto what i did it looks pretty good XD

btw you need one more "end" for it to work

No problem! :)

@QuentinADay (View Post)

 I always make these mistakes with out my lovly notepad++

lol i use sublime text 2 it works really well and i love it