feat: add if statements

examples/04_if_else.peb

@@ -3,7 +3,7 @@ let age = 14
 if age >= 18 {
     print("You are an adult")
 } else {
-    print("You are a child)
+    print("You are a child")
 }
 
 let guess = 12

main.py

@@ -13,7 +13,7 @@ def main():
     123
     "This is
      another string" """
-    path: str = "examples/08_scopes.peb"
+    path: str = "examples/04_if_else.peb"
     with open(path, "r") as f:
         source = f.read()
     lexer: Lexer = Lexer()

src/ast/stmt.py

@@ -25,6 +25,10 @@ class Stmt(ABC):
         def visit_expression_stmt(self, stmt: ExpressionStmt) -> T:
             ...
 
+        @abstractmethod
+        def visit_if_stmt(self, stmt: IfStmt) -> T:
+            ...
+
         @abstractmethod
         def visit_print_stmt(self, stmt: PrintStmt) -> T:
             ...
@@ -50,6 +54,16 @@ class ExpressionStmt(Stmt):
         return visitor.visit_expression_stmt(self)
 
 
+@dataclass(frozen=True)
+class IfStmt(Stmt):
+    condition: Expr
+    then_branch: Stmt
+    else_branch: Optional[Stmt]
+
+    def accept(self, visitor: Stmt.Visitor[T]) -> T:
+        return visitor.visit_if_stmt(self)
+
+
 @dataclass(frozen=True)
 class PrintStmt(Stmt):
     expression: Expr

src/interpreter/interpreter.py

@@ -1,7 +1,7 @@
 from typing import Any
 
 from src.ast.expr import LiteralExpr, GroupingExpr, UnaryExpr, BinaryExpr, Expr, VariableExpr, AssignExpr
-from src.ast.stmt import Stmt, PrintStmt, ExpressionStmt, LetStmt, BlockStmt
+from src.ast.stmt import Stmt, PrintStmt, ExpressionStmt, LetStmt, BlockStmt, IfStmt
 from src.interpreter.environment import Environment
 from src.interpreter.error import PebbleRuntimeError
 from src.pebble import Pebble
@@ -108,6 +108,12 @@ class Interpreter(Expr.Visitor[Any], Stmt.Visitor[None]):
     def visit_expression_stmt(self, stmt: ExpressionStmt) -> None:
         self.evaluate(stmt.expression)
 
+    def visit_if_stmt(self, stmt: IfStmt) -> None:
+        if self.is_truthy(self.evaluate(stmt.condition)):
+            self.execute(stmt.then_branch)
+        elif stmt.else_branch is not None:
+            self.execute(stmt.else_branch)
+
     def visit_print_stmt(self, stmt: PrintStmt) -> None:
         value: Any = self.evaluate(stmt.expression)
         print(value)

src/parser/parser.py

@@ -1,7 +1,7 @@
 from typing import Optional
 
 from src.ast.expr import Expr, BinaryExpr, UnaryExpr, LiteralExpr, GroupingExpr, VariableExpr, AssignExpr
-from src.ast.stmt import Stmt, PrintStmt, ExpressionStmt, LetStmt, BlockStmt
+from src.ast.stmt import Stmt, PrintStmt, ExpressionStmt, LetStmt, BlockStmt, IfStmt
 from src.parser.error import ParsingError
 from src.pebble import Pebble
 from src.token import Token, TokenType
@@ -107,12 +107,22 @@ class Parser:
         return LetStmt(name, initializer)
 
     def statement(self) -> Stmt:
+        if self.match(TokenType.IF):
+            return self.if_stmt()
         if self.match(TokenType.PRINT):
             return self.print_stmt()
         if self.match(TokenType.LEFT_BRACE):
             return self.block_stmt()
         return self.expression_stmt()
 
+    def if_stmt(self) -> Stmt:
+        condition: Expr = self.expression()
+        then_branch: Stmt = self.statement()
+        else_branch: Optional[Stmt] = None
+        if self.match(TokenType.ELSE):
+            else_branch = self.statement()
+        return IfStmt(condition, then_branch, else_branch)
+
     def print_stmt(self) -> Stmt:
         self.consume(TokenType.LEFT_PAREN, "Missing parentheses")
         value: Expr = self.expression()