IIF is the function:
#AppType Console
Randomize
Print $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("0"), %Asc("9"))), $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("A"), %Asc("Z"))), $Chr(%RandInt(%Asc("a"), %Asc("z")))))
Print $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("0"), %Asc("9"))), $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("A"), %Asc("Z"))), $Chr(%RandInt(%Asc("a"), %Asc("z")))))
Print $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("0"), %Asc("9"))), $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("A"), %Asc("Z"))), $Chr(%RandInt(%Asc("a"), %Asc("z")))))
Print $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("0"), %Asc("9"))), $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("A"), %Asc("Z"))), $Chr(%RandInt(%Asc("a"), %Asc("z")))))
Print $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("0"), %Asc("9"))), $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("A"), %Asc("Z"))), $Chr(%RandInt(%Asc("a"), %Asc("z")))))
Print $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("0"), %Asc("9"))), $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("A"), %Asc("Z"))), $Chr(%RandInt(%Asc("a"), %Asc("z")))))
Print $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("0"), %Asc("9"))), $IIf(%RandInt(0, 1), $Chr(%RandInt(%Asc("A"), %Asc("Z"))), $Chr(%RandInt(%Asc("a"), %Asc("z")))))
Pause
Typical outputs:
U
s
L
7
i
0
q
Press any key to continue...
or
7
q
n
7
i
0
s
Press any key to continue...
I've no idea tho how even the distribution would be.