Please, not another one;
Thailand's 20 or so constitutions and charters can be categorized into three groups:
Evolution of Thai constitutions since 1932
Elected legislatures: The legislature is completely elected. This included the 1946 Constitution where the elected House selected the Senate and the 1997 Constitution where both the House and Senate are elected.
The prime minister is either a military leader or a figurehead of the military or the palace.
This includes the 1932 constitution (after 1937), the 1947 Charter, the 1949 Constitution, the 1952 Constitution, the 1968 Constitution, the 1974 Constitution, the 1978 Constitution, the 1991 Constitution, the 2007 Constitution, and the Pending 2016 Constitution.
Absolute executives: The executive has absolute or near absolute power, with either no legislature or a completely appointed legislature. The prime minister is usually a military leader or a figurehead of the military or the palace. This includes the 1932 Charter, the 1932 constitution (before 1937), the 1959 Charter, the 1972 Charter, the 1976 Constitution, the 1991 Charter, the 2006 Interim Charter, and the 2014 Interim Constitution.