hw6: add w5.py

HW/6/w5.py

@@ -1,18 +1,42 @@
 from eval_def import *
 
 def make_a_list() -> A_List:
-    raise NotImplementedError
+    return []
+
+
+def lookup(a_list: A_List, ast: str) -> S_Expression:
+    for s, val in reversed(a_list):
+        if s == ast:
+            return val
+    raise Undefined
+
 
 def normalize(ast: AST) -> AST:
-    raise NotImplementedError
+    if isinstance(ast, Atom):
+        ast = ast.upper()
+        if set(ast) - ALLOWED_CHARS:
+            raise IllegalSymbol
+        return ast
+    else:
+        return [normalize(x) for x in ast]
 
-def lookup(a_list: A_List, name: str) -> S_Expression:
-    raise NotImplementedError
 
-def eval_cond(a_list: A_List, args: List[AST]) -> S_Expression:
+def eval_set(a_list: A_List, args: List[AST]) -> S_Expression:
     from eval import eval_rec
-    raise NotImplementedError
+    if len(args) != 2:
+        raise WrongNumberOfArguments
+    name = eval_rec(a_list, args[0])
+    if isinstance(name, S_Atom):
+        value = eval_rec(a_list, args[1])
+        a_list.append((name.value, value))
+        return value
+    else:
+        raise NotASymbol
 
-def eval_set(a_list: A_List, args: List[AST]) -> S_Expression:
+
+def eval_cond(a_list: A_List, args: List[AST]) -> S_Expression:
     from eval import eval_rec
-    raise NotImplementedError
+    for t, v, *_ in args:
+        if eval_rec(a_list, t) != NIL:
+            return eval_rec(a_list, v)
+    return NIL