You can use 'local' to have sane scoping (shadowing) in moonscript though:

    -- will print:
    -- 15
    -- 0
    -- 15
    -- 10

    y = 0
    goodfun = (x) ->
        local y
        y = 10
        y + x
    
    badfun = (x) ->
        y = 10
        y + x
    
    print(goodfun(5))
    print(y)
    print(badfun(5))
    print(y)