Arithmetic Expression Compiler (Python)

A compiler pipeline for arithmetic expressions implemented entirely in Python with no external dependencies. The system performs lexical analysis, LL(1) recursive-descent parsing, 3-address intermediate code (IR) generation, and IR execution — exposed through an interactive REPL.

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Tech Stack

Component	Technology
Language	Python 3 (stdlib only)
Lexer	Regular expressions (re module)
Parser	LL(1) recursive descent
IR	3-address code with named temporaries
Interface	Interactive REPL (stdin/stdout)
Tests	unittest (standard library)

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Supported Language

Feature	Details
Literals	Non-negative integers (0, 42, 999)
Operators	Addition (+), Multiplication (*)
Grouping	Parentheses ( )
Precedence	* binds tighter than +

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Grammar (LL(1))

The grammar is factored to eliminate left recursion and encode operator precedence:

E  → T E'
E' → + T E' | ε
T  → F T'
T' → * F T' | ε
F  → number | ( E )

E handles addition, T handles multiplication, and F handles atoms (literals and parenthesized sub-expressions). This structure guarantees correct precedence without any post-processing.

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Compilation Pipeline

Input string
    │
    ▼
[Lexer]  analisador_lexico.py
    │  Tokenizes input into: NUMBER, PLUS, STAR, LPAREN, RPAREN, EOF
    │
    ▼
[Parser] analisador_sintatico.py
    │  LL(1) recursive descent; drives IR generation during parsing
    │
    ▼
[IR Generator] codigo_intermediario.py
    │  Emits 3-address instructions: tN = operand op operand
    │
    ▼
[IR Executor]
    │  Evaluates the instruction list; returns the value of the last temporary
    │
    ▼
Result

Example — 2 + 3 * 4

Generated IR:

t1 = 2
t2 = 3
t3 = 4
t4 = t2 * t3
t5 = t1 + t4

Result: t5 = 14

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Project Structure

python-expression-compiler/
├── main.py                          # Entry point, launches the REPL
├── requirements.txt                 # Empty (no external dependencies)
├── src/tradutor_expressoes/
│   ├── tokens.py                    # Token type definitions
│   ├── analisador_lexico.py         # Lexer (tokenizer)
│   ├── analisador_sintatico.py      # Parser (LL(1) recursive descent)
│   ├── codigo_intermediario.py      # 3-address IR generator and executor
│   ├── interface_repl.py            # REPL loop
│   ├── erros.py                     # Error types (LexicalError, SyntaxError)
│   └── utils.py                     # Shared utilities
└── tests/
    ├── teste_analisador_lexico.py
    ├── teste_avaliacao_expressao.py
    ├── teste_erros_sintaticos.py
    └── teste_interface_repl.py

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Running

Standard mode

python main.py

The REPL reads one expression per line, prints the result, and loops. On error, prints a diagnostic and continues.

> 2 + 3 * 4
Expressão válida. Resultado: 14

> (1 + 2) * (3 + 4)
Expressão válida. Resultado: 21

> 2 +
Erro sintático: token inesperado após '+'

Debug mode

Prints the token stream and full IR listing before the result:

python main.py --debug

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Running Tests

# Run all tests
python -m pytest tests/

# Run a single test file
python -m pytest tests/teste_analisador_lexico.py

# Run with verbose output
python -m pytest tests/ -v

No installation required — all dependencies are part of the Python standard library.