Why Pascal Doesn't Support ADTs

• Pascal lacks an encapsulation mechanism that forces the programmer to use only specific procedures when referencing variables of a given type.

• There is no way to declare variables that persist during the entire execution of a program without making them globally accessible to all procedures. (That is, a global variable lives forever but is globally accessible, while a local variable has restricted access, but only lives during the lifetime of the procedure in which it is declared.)

• It isn't possible to group all the information about a type in one place (since all consts, types, and vars must be declared together).

• Pascal lacks a language-defined scheme for separate compilation, so it isn't possible to build a library of data types for use by any Pascal program.