.he 'MISHAP045''Page %'
.fo 'Aaron Sloman''February 78'
.sp
: 45 	Non numbers for arithmetic operation
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Only numbers can be added subtracted multiplied or divided.
So if you try to add a number to a word or a list or a
function, or an "undef" object, you'll get this error.
e.g. you type something like "x + 1 -> x;" before
you've assigned a number to x. (Try it.)
Have you perhaps tried to add a list to a number, e.g.
 	function addup (numlist);
 		if	numlist= []
 		then	[]
 		else	hd(numlist) + addup(tl(numlist))
 		close
 	end;
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then
 	addup([1 2 3]) =>
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produces an error because you've used [] instead of 0 as the
result of addup for an empty list. Try it, with tracing.
Try also
 	hd([[1 2] 3]) + 5 =>
 	3 + "three" =>
