From dfb5ee45fb68aca09bd0ac9967c6b574f932d39f Mon Sep 17 00:00:00 2001
From: Frederick Yin <fkfd@fkfd.me>
Date: Sat, 3 Sep 2022 11:46:10 +0800
Subject: hackc: While statement

---
 projects/hackc/statements.py | 55 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 54 insertions(+), 1 deletion(-)

(limited to 'projects/hackc/statements.py')

diff --git a/projects/hackc/statements.py b/projects/hackc/statements.py
index 0e257ed..458ba01 100644
--- a/projects/hackc/statements.py
+++ b/projects/hackc/statements.py
@@ -8,7 +8,13 @@ class Statement:
 
     @classmethod
     def from_tokens(cls, tokens: list) -> tuple:
-        for StatementClass in [LetStatement, DoStatement, ReturnStatement, IfStatement]:
+        for StatementClass in [
+            LetStatement,
+            DoStatement,
+            ReturnStatement,
+            IfStatement,
+            WhileStatement,
+        ]:
             stmt, dt = StatementClass.from_tokens(tokens)
             if stmt is not None:
                 return (stmt, dt)
@@ -35,6 +41,8 @@ class StatementList:
     def print_verbose(self):
         for stmt in self.statements:
             stmt.print_verbose()
+        if not self.statements:
+            print("Do nothing")
 
 
 class LetStatement:
@@ -190,3 +198,48 @@ class IfStatement:
         if self.else_then is not None:
             print("Else then:")
             self.else_then.print_verbose()
+        print("End if")
+
+
+class WhileStatement:
+    def __init__(self, condition: Expression, do: StatementList):
+        self.condition = condition
+        self.do = do
+
+    @classmethod
+    def from_tokens(cls, tokens: list) -> tuple:
+        """Construct while statement.
+
+        Format:
+        'while' '(' <expression> ')' '{' <statement list> '}'
+        """
+        if len(tokens) < 6 or tokens[0] != "while":
+            return (None, 0)
+
+        if tokens[1] != LEFT_PAREN:
+            raise UnexpectedToken(LEFT_PAREN, tokens[1])
+
+        t = 2
+        cond, dt = Expression.from_tokens(tokens[2:])
+        if cond is None:
+            raise JackSyntaxError(f"Expected condition", tokens[2])
+        t += dt
+
+        if tokens[t] != RIGHT_PAREN:
+            raise UnexpectedToken(RIGHT_PAREN, tokens[t])
+        if tokens[t + 1] != LEFT_BRACE:
+            raise UnexpectedToken(LEFT_BRACE, tokens[t + 1])
+        t += 2
+
+        do, dt = StatementList.from_tokens(tokens[t:])
+        t += dt
+
+        if tokens[t] != RIGHT_BRACE:
+            raise UnexpectedToken(RIGHT_BRACE, tokens[t])
+
+        return (WhileStatement(cond, do), t + 1)
+
+    def print_verbose(self):
+        print(f"While {self.condition} do:")
+        self.do.print_verbose()
+        print("End while")
-- 
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