secd/doc/ideas.md

# Goals

* Be an efficent compilation target for typed lambda calculi

* Be substantially easier to translate to than machine code.

* Run cross-platform on as many operating systems and architectures as possible. (bare minimum 32-bit).

* Allow for code completely independent of the host machine.

* Leave memory managment out of the question for the compiler writer.

* Provide significant IO functionality.

* Provide efficient native methods for manipulating commonly used types
  * Strings (don't represent as a list of characters, god)
  * Characters
  * Integers
  * Floating point numbers
  * Raw bytes
  * Lists (cons linked list), efficient map, foldr, and filter instructions would be nice
  * Arrays (constant lookup continous memory)

* Have methods for representing algebraic data types built into the machine.
  * Sums and products of arbitrary size, and methods for (de)constructing them.
  * Sums as tagged pairs since the machine is untyped

* Instruction for tail recursion which takes the new parameters of the stack and resets the C pointer to where it last entered a closure.

* Recursion instruction which functions as dup : app

* GMP arithmetic

* Some sort of pattern matching facility for matching on the first element of a pair, (the constructor).

# Non-Goals

* Safely error out or leave catchable exceptions when instruction is called with wrongful operands.

* Dynamic linking, creating object files with polymorphic types.

* Lazy evaluation.

# Nicities (plausible)

* Provide a compiler from a simply typed lambda calculus, coupled with a small standard library which would confirm type safety of all used instructions. Maybe go even further? System F?

* Maybe some vector operations? You could reasonably operate on chunks of the stack.

# Nicities (dreaming)

* Provide more complete IO functionality, such as networking, etc. (this is not likely to happen)

* Provide some sort of FFI (this is not likely to happen)

* It's possible one might be able to JIT compile some stuff?

# Encoding stuff

* Common instructions are 1 byte and a lookup table is used to run a function executing said instruction. Less common instructions will have the first byte take them to a function which reads the next byte, allowing for a tree of instructions.

* All words realistically **have** to be the same size for the stack to make sense. Which size should be used? This feels like it could easily become machine dependant.
  * Possibly go for the highest you have, 8 bytes? Would mean that performance would be god awful on 32 bit machines. I might be ok with that? Am I?
  * What about byte types, etc? Should we really allow that? It becomes a pain. Perhaps it is easiest to pretend computers do not exist and only deal with numbers? Only use GMP arithmetic then?
    * Possible set of builtin types:
      * Int64    - 64-bit signed integer
      * Word64   - 64-bit unsigned integer
      * Float    - 64-bit double precision floating point number
      * Integer  - GMP
      * Natural  - GMP
      * Float    - GMP
      * Rational - GMP
      * String   - Like Data.Text
      * Char     - 64-bit unicode codepoint.
      * List     - Pointer to linked list
      * Array    - Pointer to length tagged constant memory
      * Pair     - Pointer to constant memory of length 2

# File Format stuff

* Much like ELF, start of with header containing basic info, reserve some bytes for future additions, have field specifing version. Then have sections.

* Code section, the initial C stack.

* Global section, the initial G env.

* Linkable and Executable. Linkables have some sort of symbol table for wanted symbols, as well as a list of files it wishes to link with. The linker, or perhaps the VM, when loading, will then lookup these files in a global search path, perform substitution with the symbols to create an Executable file with a complete global table.

* Must realise an encoding for closures, products and GMP numbers to be used in globals.