BUILTINS.md

Setting a variable

set/2	Set VariableName to Value. If it is defined in the parent
        scope, it will be updated there. Otherwise, it is created
        in the current scope.

(set VariableName Value)

Caveats: May set VariableName if it is already defined up the parent
         scope (ie, used by another function.)
Workaround: Use var/2 instead.


var/2	Set VariableName to Value in the current scope. This will
        define a new variable in the current scope, or update a
        variable of that name in the current scope.

(var VariableName Value)

Caveats: Since it is set in the current scope, you may end up unintentionally
         creating a new variable because your current scope has changed.
Workaround: Use var/2 to create a variable initially, and then use set/2 to
            update it. It will walk up the chain to the most recently defined
            VariableName, and update that one.