From cb320b921c0574474430fe8d38aa5438a9f6ee98 Mon Sep 17 00:00:00 2001
From: Frederick Yin <fkfd@fkfd.me>
Date: Tue, 30 Aug 2022 15:39:10 +0800
Subject: hackc: var declaration in/out of subroutine

---
 projects/hackc/syntax.py | 39 ++++++++++++++++++++++++---------------
 1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/projects/hackc/syntax.py b/projects/hackc/syntax.py
index a07e69e..281bd17 100644
--- a/projects/hackc/syntax.py
+++ b/projects/hackc/syntax.py
@@ -29,12 +29,10 @@ class Class:
             raise JackSyntaxError(
                 f"Expected `class`, got `{tokens[0]}` instead", tokens[0]
             )
-        if tokens[1].type != "identifier":
-            raise JackSyntaxError(
-                f"You cannot name a class `{tokens[1]}`", tokens[1]
-            )
 
         name = tokens[1]
+        if name.type != "identifier":
+            raise JackSyntaxError(f"You cannot name a class `{name}`", name)
 
         if tokens[2] != LEFT_BRACE:
             raise JackSyntaxError(
@@ -44,7 +42,9 @@ class Class:
         tokens_consumed = 3
 
         while True:
-            variables, token_cnt = Variable.from_tokens(tokens[tokens_consumed:])
+            variables, token_cnt = Variable.from_tokens(
+                tokens[tokens_consumed:], context="class"
+            )
             if variables is None:
                 break
             variables.print_verbose()
@@ -60,9 +60,12 @@ class Variable:
         self.names = names
 
     @classmethod
-    def from_tokens(cls, tokens: list) -> tuple:
-        """Construct variable declaration statement.
-        Return a tuple of a Variable instance and number of tokens consumed.
+    def from_tokens(cls, tokens: list, context: str) -> tuple:
+        """Construct variable declaration statement from a list of tokens.
+        Return a tuple of an instance of Variable and number of tokens consumed.
+        When `tokens` does not begin with a variable declaration, return (None, 0).
+
+        context -- "class" (<scope> = static | field) or "subroutine" (<scope> = var)
 
         Format:
         <scope> <type> <one or more names, joined with a comma>;
@@ -75,13 +78,19 @@ class Variable:
             return (None, 0)
 
         scope = tokens[0]
-
-        if tokens[1] not in PRIMITIVE_TYPES and tokens[1].type != "identifier":
+        if scope in ["static", "field"] and context != "class":
             raise JackSyntaxError(
-                f"Expected datatype, got `{tokens[1]}` instead", tokens[1]
+                f"You cannot declare a {scope} variable in a subroutine", scope
+            )
+        if scope == "var" and context != "subroutine":
+            raise JackSyntaxError(
+                f"You cannot declare a local variable outside of a subroutine",
+                scope,
             )
 
         type = tokens[1]
+        if type not in PRIMITIVE_TYPES and type.type != "identifier":
+            raise JackSyntaxError(f"Expected datatype, got `{tokens[1]}` instead", type)
 
         tokens_consumed = 2
         names = []  # names of variables
@@ -94,9 +103,7 @@ class Variable:
                     names.append(token)
                     expecting_identifier = False
                 else:
-                    raise JackSyntaxError(
-                        f"Expected `,`, got `{token}` instead", token
-                    )
+                    raise JackSyntaxError(f"Expected `,`, got `{token}` instead", token)
             elif token == ",":
                 if not expecting_identifier:
                     expecting_identifier = True
@@ -112,7 +119,9 @@ class Variable:
                 break
             else:
                 expected = "variable name" if expecting_identifier else "`,` or `;`"
-                raise JackSyntaxError(f"Expected {expected}, got `{token}` instead", token)
+                raise JackSyntaxError(
+                    f"Expected {expected}, got `{token}` instead", token
+                )
 
         return (Variable(scope, type, names), tokens_consumed)
 
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