Put another way, if you see sigma in an APL program, you can understand what that is without knowing its context. Single characters in J do not have this property; < is different from <. is different from <: (and sometimes surprisingly different; =. defines a local and =: defines a global), and in a lot of fonts it's not hard to mistake one for the other.
J, to me, took the worst features of APL (the profusion of symbols that only loosely resemble anything else you've ever seen) and makes it even worse, because at least the APL symbols were (usually) visually distinct! From the J examples page are gems like this
var =: ~.@(] , |:&.> , |.&.> , |."1&.>)^:3
which in the proportional font they use makes for a real entertaining time telling , from ,. from ..
J, to me, took the worst features of APL (the profusion of symbols that only loosely resemble anything else you've ever seen) and makes it even worse, because at least the APL symbols were (usually) visually distinct! From the J examples page are gems like this
which in the proportional font they use makes for a real entertaining time telling , from ,. from ..