get better declaration structure

[Memorytaco]

So for compilation, we need a store to hold all knowledge we know, like all data structures we user has defined and how they are used. A good holder for all items is quite important for following compiling process.

We define these structures for the module:

• lexical item

  the operator (for now)

• data structure definition

  including concrete data (like records and variants but with names) and opaque type (it acts like struct type; in C)

• type alias definition or type function (temporary thoughts)

  It distinguishes concrete type names from reducible type functions.

• FFI item

  our first FFI target should be The C Programming Language. this FFI should be able to handle low level function call directly and also the value.

• value definition

  difference from haskell or c or c++, the language doesn't distinguish between function and value. function is merely a lambda block. Since lambda itself can't do recursive thing, so we expand let to allow recursive definition.

[Memorytaco]

Done, see Refresh declaration structure and Refine definition of Module structure .