3.8 KiB
| layout | title |
|---|---|
| soml | Salama object machine language |
Disclaimer
The som Language was a stepping stone: it will go. The basic idea is good and will stay, but the parser, and thus it's existence as a standalone language, will go.
What will remain is traditionally called an intermediate representation. Basically the layer into which the soml compiler compiles to. As such these documents will be rewritten soon.
Top down designed language
Soml is a language that is designed to be compiled into, rather than written, like other languages. It is the base for a higher system, designed for the needs to compile ruby. It is not an endeavor to abstract from a lower level, like other system languages, namely off course c.
Still it is a system language, or an object machine language, so almost as low level a language as possible. Only assembler is really lower, and it could be argued that assembler is not really a language, rather a data format for expressing binary code.
Object oriented to the core, including calling convention
Soml is completely object oriented and strongly typed. Types are modelled as classes and carry information about instance variable names and their basic type. Every object stores a reference to it's types, and while types are immutable, the reference may change. The basic types every object is made up off, include at least integer and reference (pointer).
The object model, ie the basic properties of objects that the system relies on, is quite simple and explained in the runtime section. It involves a single reference per object. Also the object memory model is kept quite simple in that objects are always small multiples of the cache size of the hardware machine. We use object encapsulation to build up larger looking objects from these basic blocks.
The calling convention is also object oriented, not stack based*. Message objects used to define the data needed for invocation. They carry arguments, a frame and return addresses. In Soml return addresses are pre-calculated and determined by the caller, and yes, there are several. In fact there is one return address per basic type, plus one for exception. A method invocation may thus be made to return to an entirely different location than the caller. *(A stack, as used in c, is not typed and as such a source of problems)
There is no non- object based memory in soml. The only global constants are instances of classes that can be accessed by writing the class name in soml source.
Syntax and runtime
Soml syntax is a mix between ruby and c. I is like ruby in the sense that semicolons and even newlines are not neccessary unless they are. Soml still uses braces, but that will probably be changed.
But off course it is typed, so in argument or variable definitions the type must be specified like in c. Type names are the class names they represent, but the "int" may be used for brevity instead of Integer. Return types are also declared, though more for static analysis. As mentioned a function may return to different addresses according to type. The compiler automatically inserts errors for return types that are not handled by the caller. The complete syntax and their translation is discussed here
As soml is the base for dynamic languages, all compile information is recorded in the runtime. All information is off course object oriented, ie in the form off objects. This means a class hierarchy, and this itself is off course part of the runtime. The runtime, Parfait, is kept to a minimum, currently around 15 classes, described in detail here.
Historically Parfait has been coded in ruby, as it was first needed in the compiler. This had the additional benefit of providing solid test cases for the functionality. Currently the process is to convert the code into soml, using the same compiler used to compile ruby.