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goals o code reuse o enabling collaboration between users o generic collection types o encapsulation

visibility o “my script” can reference a library script “foo v1.0” under the name “foo” o public action “frobnicate” from “foo v1.0” is visible as “foo→frobnicate” in “my script” o global variables, events, art, and private actions are not visible outside defining library script

sharing o the same library script can be referenced multiple times giving it multiple copies of global variables and tables o “my script” references libraries “nice circle” and “super square” which in turn both reference “logo turtle” “my script” decides if there is one or two copies of “logo turtle” (and thus one or two turtles running around on the screen)

sharing in ui circlesquare loc_turtle

rebinding o if “nice circle” and “super square” reference slightly different versions of “logo turtle” they can still be bound to one in “my script” if signatures match there is no problem otherwise rebinding of particular actions is possible

rebinding in ui default binding rebound

funtors o they are like ML functors but much more fun o main script controls dependencies of referenced libraries which makes them parametric lib #0 main script lib #1lib #2 o references can be resolved back into main script

funtor details o required signatures are implicit o funtor parameters come with defaults you can replace actions in referenced libraries, but if you don’t, there always the default implementation