Alpha Language Compiler & Virtual Machine

A complete compiler and virtual machine for the Alpha language, built as part of the HY-340 Languages & Compilers course at the University of Crete.

Building

Requires gcc, flex, and bison.

make

This produces:

• compiler.exe — the Alpha compiler
• vm.exe — the Alpha virtual machine

To clean build artifacts:

make clean

Usage

Compile an Alpha source file (.asc):

./compiler.exe your_program.asc

This generates binary.abc (bytecode).

Run the bytecode:

./vm.exe binary.abc

Example:

echo 'print("Hello Alpha!\n");' > hello.asc
./compiler.exe hello.asc
./vm.exe binary.abc

Project Structure

src/        Compiler source (lexer, parser, semantic analysis, code generation)
vm/         Virtual machine source
include/    Shared header files
tests/      Test programs
Makefile    Top-level build

Pipeline

Source (.asc) → Lexer (Flex) → Parser (Bison) → Semantic Analysis
             → Intermediate Code (Quads) → Code Generation → Bytecode (.abc)
             → Virtual Machine (AVM)

Implemented Features

• Numerical calculations and arithmetic (including % with correct signed semantics)
• All library functions: print, input, typeof, objectmemberkeys, objecttotalmembers, objectcopy, totalarguments, argument, strtonum, sqrt, cos, sin
• User-defined functions (including anonymous and nested functions)
• Recursive functions
• Simple tables (associative arrays)
• Logic statements (and, or, not)
• while loops and for loops
• break / continue
• Scope rules (local, :: global access)

Known Limitations

• Complex nested table operations and the table-as-functor pattern (obj(args) calling via "()" key) are not fully supported
• Some advanced table-heavy test files (tables1.asc, delegation.asc) do not run completely

Bug Fixes

The following bugs were identified and fixed after the initial implementation:

#	Location	Description
1	vm/avm_functions.c	avm_callsaveenvironment stored a wrong savedTop value, corrupting the caller's stack frame on every user-function return
2	vm/avm_execution.c	execute_mod cast operands to unsigned before %, producing wrong results for negative values; fixed with fmod
3	vm/avm_execution.c	execute_pusharg reset avm_totalActuals by inspecting code[pc-1] (physically adjacent instruction), which is unreliable after jumps; combined with a proper reset in execute_funcexit
4	src/rule_handler.c	countDigits(0) returned 0, causing malloc(2) for the string "$0\0" (3 bytes) — heap overflow on the first anonymous function
5	vm/avm_execution.c	execute_mod used unsigned cast instead of fmod, giving wrong results for negative operands
6	vm/avm.c	avm_translate_operand called strdup for string_a operands without first calling avm_memcellclear, leaking one heap allocation per string-constant read
7	vm/avm_execution.c	execute_call had a string_m case that silently dispatched any string value as a library function name; replaced with a proper type error
8	src/target.c	consts_newstring, consts_newnumber, and libfuncs_newused did not check realloc's return value, leaking memory and crashing on allocation failure
9	src/rule_handler.c	Relational-operator error messages indexed str_iopcodeName[] (opcode names) with an ExprType value; fixed by introducing a dedicated str_ExprTypeName[] array
10	vm/avm_execution.c	execute_funcenter contained a no-op if (avm_totalActuals == 0) avm_totalActuals = 0 branch

License

This project is released under the MIT License.