feat: add class constructor

examples/basic/20_init.peb

@@ -0,0 +1,20 @@
+class Person {
+    init(firstname, lastname) {
+        this.firstname = firstname
+        this.lastname = lastname
+    }
+
+    get_fullname() {
+        return this.firstname + " " + this.lastname
+    }
+
+    greet(person) {
+        print("Hello " + person.get_fullname())
+    }
+}
+
+let alice = Person("Alice", "Foo")
+let bob = Person("Bob", "Bar")
+
+alice.greet(bob)
+bob.greet(alice)

main.py

@@ -4,7 +4,7 @@ from src.pebble import Pebble
 
 
 def main():
-    path: Path = Path("examples/basic/19_this.peb")
+    path: Path = Path("examples/basic/20_init.peb")
     Pebble.run_file(path)
 
 

src/consts.py

@@ -1 +1,2 @@
 MAX_FUNCTION_ARGS = 255
+CONSTRUCTOR_NAME = "init"

src/core/function.py

@@ -13,9 +13,10 @@ if TYPE_CHECKING:
 
 
 class PebbleFunction(PebbleCallable):
-    def __init__(self, declaration: FunctionStmt, closure: Environment):
+    def __init__(self, declaration: FunctionStmt, closure: Environment, is_init: bool = False):
         self.declaration: FunctionStmt = declaration
         self.closure: Environment = closure
+        self.is_init: bool = is_init
 
     def arity(self) -> int:
         return len(self.declaration.params)
@@ -29,6 +30,9 @@ class PebbleFunction(PebbleCallable):
             interpreter.execute_block(self.declaration.body, env)
         except ReturnException as ret:
             return ret.value
+
+        if self.is_init:
+            return self.closure.get_at(0, "this")
         return None
 
     def __str__(self):
@@ -37,4 +41,4 @@ class PebbleFunction(PebbleCallable):
     def bind(self, instance: PebbleInstance):
         env: Environment = Environment(self.closure)
         env.define("this", instance)
-        return PebbleFunction(self.declaration, env)
+        return PebbleFunction(self.declaration, env, self.is_init)

src/core/klass.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 from typing import Any, TYPE_CHECKING, Optional
 
+from src.consts import CONSTRUCTOR_NAME
 from src.core.callable import PebbleCallable
 from src.core.function import PebbleFunction
 from src.core.instance import PebbleInstance
@@ -19,10 +20,16 @@ class PebbleClass(PebbleCallable):
         return self.name
 
     def arity(self) -> int:
-        return 0
+        initializer: Optional[PebbleFunction] = self.find_method(CONSTRUCTOR_NAME)
+        if initializer is None:
+            return 0
+        return initializer.arity()
 
     def call(self, interpreter: Interpreter, arguments: list[Any]) -> Any:
         instance: PebbleInstance = PebbleInstance(self)
+        initializer: Optional[PebbleFunction] = self.find_method(CONSTRUCTOR_NAME)
+        if initializer is not None:
+            initializer.bind(instance).call(interpreter, arguments)
         return instance
 
     def find_method(self, name: str) -> Optional[PebbleFunction]:

src/interpreter/interpreter.py

@@ -4,6 +4,7 @@ from src.ast.expr import LiteralExpr, GroupingExpr, UnaryExpr, BinaryExpr, Expr,
     CallExpr, GetExpr, T, SetExpr, ThisExpr
 from src.ast.stmt import Stmt, ExpressionStmt, LetStmt, BlockStmt, IfStmt, WhileStmt, ForStmt, FunctionStmt, \
     ReturnStmt, BreakStmt, ContinueStmt, ClassStmt
+from src.consts import CONSTRUCTOR_NAME
 from src.core.callable import PebbleCallable
 from src.core.function import PebbleFunction
 from src.core.instance import PebbleInstance
@@ -179,7 +180,7 @@ class Interpreter(Expr.Visitor[Any], Stmt.Visitor[None]):
         self.env.define(stmt.name.lexeme, None)
         methods: dict[str, PebbleFunction] = {}
         for method in stmt.methods:
-            func: PebbleFunction = PebbleFunction(method, self.env)
+            func: PebbleFunction = PebbleFunction(method, self.env, method.name.lexeme == CONSTRUCTOR_NAME)
             methods[method.name.lexeme] = func
         klass: PebbleClass = PebbleClass(stmt.name.lexeme, methods)
         self.env.assign(stmt.name, klass)