hpersh/oovm40

OOVM language

Part I - Library For Object-Oriented VM

VM model

Memory

Instances

Objects

Threads

Instance stack

Frame stack

Operating with C

Built-in classes

Metaclass

Object

Boolean

Integer

API

Part II - Compiler for Object-oriented Language

Language

Goals

• Minimal
  • Keep language simple
• Consistent
  • Everything is an object

Influences

• Syntax: C, simplified a bit, with additions
  • Assignments are statements, not expressions
  • "if", "while", "for", etc. require block with curly braces
  • "return" requires expression in parentheses
  • Additional keywords begin with '@', e,g. "@class", "@method"

Sample

hello.ovm

// Yes, of course there are comments

@class Start
{
    @classmethod start(cls)
    {
        "Hello, world!\n".print();
    }
}

Components

• oovm.[ch]: source for VM
• .libs/liboovm.so: VM runtime
• .libs/liboovmmodule.so: compiled module module
• ovmc1, ovmc[2-5].py: Source code compiler
• oovm: Executable to load initial module, and run initial method
• *.c, *.ovm: Module source

How to build basic system

1. make all

How to build and run a new module

1. Create module source file, eg. module.ovm
2. Build module, e.g. ovmc module.ovm; resulting shared lib is in .libs subdirectory
3. Run module, e.g. oovm module[.class[.method]] [arg ...]
   • class and method default to "Start" and "start", respectively

Environment variable OVM_MODULE_PATH must include location(s) for libraries for required modules, liboovmmodule.so

Exceptions

System exceptions

system.invalid-value

A method was given an invalid value, usually of the wrong type. The attribute inst contains the offending instance.

system.no-method

A call was made for a method that is not defined. The following attributes describe the offending method call:

• receiver contains the method receiver
• selector contains the method selector

system.no-variable

An attempt was made to read a non-existent variable from a namespace, or the environment. The attribute name contains the name of the offending variable.

system.number-of-arguments

A method was called with the incorrect number of arguments. The following attributes describe the offending metho call:

• expected contains the number arguments the method expected, when the method expects a fixed number of arguments
• minimum contains the minimum number arguments the method expected, when the method expects a variable number of arguments
• maximum contains the minimum number arguments the method expected, when the method expects a variable number of arguments
• got contains the number of arguments the method was called with

system.no-attribute

An attribute read for an object failed, because the given object does not have the given attribute. The following attributes of the exception describe the offending access:

• instance is the object for which the access was made
• attribute is the requested attribute for the object

system.index-range

An attempt was made to access an array or slice outside its bounds. The following attributes of the exception describe the offending access:

• instance is the array or slice being accessed
• index is the starting index
• length is the number of items; only provided if it is > 1

system.key-not-found

An attempt was made to look up a key in a dictionary, and the key is not present in the dictionary. The following attributes of the exception describe the offending access:

• instance is the dictionary being accessed
• key is the offending key

system.modify-constant

An attempt was made to modify a constant entry (a entry where key begins with '#' character) in a dictionary. The following attributes of the exception describe the offending access:

• instance is the dictionary being accessed
• key is the offending key

system.file-open

Opening a file failed. The following attributes of the exception describe the offending access:

• filename is the name of the file
• mode is the file access mode
• errno is the error code returned by fopen(3)
• message is a strerror_r(3)-style error message for the failure

system.module-load

Loading a module failed.

• name is the name of the module
• message is a message describing the failure

Classes

• All classes are instances of the metaclas #Metaclass
• The parent relationship between classes is used for method search order
  • When searching for method M for an instance of class C,
    • Look in the method directory for class C
    • If not found, look in method directory of parent of C
    • Repeat moving up parents until found, stopping at #Object class, which has no parent
  • Similar process for instances that are classes, i.e. instances of #Metaclass; search uses classmethod directry for each searched class

#Metaclass

Class methodies

new(ns, name, parent)
Create a new class, which will have the given name, be entered into the given namespace, and have the given class as its parent.

at(self, name)
Return the <key, value> pair for the given class variable, or #nil if the class variable is not defined.

ate(self, name) Return the value for the given class variable; raise an exception of type

Instance methodies

#Object

@class #Object { // Allocate storage for instance @classmethod alloc();

// Initialize an instance
@method __init__(arg, ...);

// Create a new instance
// The class' __alloc__() method is called, to allocate storage for the
// instance, and then the __init__() method is called for the new instance,
// passing the arguments given to new().
@classmethod new(arg, ...);

// Return #false if receiver is #nil, else return #true
@method Boolean();

// Return a list of pairs, of all members of the object
@method List();

}

Boolean

Bugs

• Nested functions - FIXED

To do

• Array args - DONE

• Namepsace support - DONE

• Optimization -O2 causes crash (!) - DONE

• Parsing strings into objects - DONE

• Global (module-level) functions - already supported

  • Assignment to module variable, of anonymous function

• VM instructions - DONE

• Optimize forward references in VM - DONE

• Complete test suite

• Performace

  • Inline everything except method calls

• Minor code-generation optimizations

  • Jumps to jumps
  • Straight-line, non-iterated code need not pre-allocate locals

• More string formatting features: field width, justification, etc.

• Syntactic sugar for setting global (i.e. module-level) variables

• Static builds

• Use autoconfig / automake

• Registers

  • Registers can hold values across statements, i.e. caching values instead of repeatedly evaluating expressions/statements
  • Compiler must track and re-use register contents