foreach - Netlogo - expected constant error -

i have line of code:

set ssb sum [foreach  [foglie [ipotetico? = false]] [((([media] of self ) - media-tot ) ^ 2) * ([larg] of self * [altez] of self)]] 

• foglie agentlist;
• media-tot global variable

i cannot figure out why gives me error:

expected constant

i found following loophole looks me not elegant , maybe slower:

set ssb 0 ask foglie [ipotetico? = false] [ set ssb (ssb + (( [media] of self - media-tot) ^ 2) * ([larg] of self * [altez] of self)) ]  

• what think?
• how can make first code work?
• is second code equivalent?

a question include minimal example of problem. in case, in first attempt above, looks not understand difference between agentsets , lists, nor use of foreach. need read this.

• sum requires list input
• to make list bracket notation, need include constants; otherwise, use list
• putting agentset in brackets not produce list, above reason, if used list list containing agentset element, not list of agents
• foreach not return list (but map does)

assuming media, larg, , altez foglie attributes , media-tot global, have done following:

sum [(media - media-tot) ^ 2 * (larg * altez)] of (foglie [ipotetico? = false])