parser: only require an iterator of tokens instead of a list

compiler/parser.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import collections.abc
 from typing import Callable
 
 from .errors import CompilationError, UnexpectedTokenError
@@ -13,20 +14,40 @@ tracer = Tracer(logger, level=LogLevel.Debug)
 
 
 class Parser:
-    def __init__(self, tokens: list[Token]):
+    def __init__(self, tokens: collections.abc.Iterator[Token]):
         self.tokens = tokens
+        self._token_cache: list[Token] = []
+        self._EOF = False
         self.pos = 0
         self._last_accepted_token: Tokens | None = None
 
     @property
     def token(self) -> Token:
-        if self.pos >= len(self.tokens):
-            return Token(kind=Tokens.EOF)
-        return self.tokens[self.pos]
+        if self._EOF:
+            return self._token_cache[-1]
+
+        while len(self._token_cache) <= self.pos:
+            tok = next(self.tokens)
+            self._token_cache.append(tok)
+            if tok.kind == Tokens.EOF:
+                self._EOF = True
+                return tok
+
+        return self._token_cache[self.pos]
+
+    def _fetch_until(self, desired_length: int) -> int:
+        while len(self._token_cache) <= desired_length and not self._EOF:
+            tok = next(self.tokens)
+            self._token_cache.append(tok)
+            if tok.kind == Tokens.EOF:
+                self._EOF = True
+                break
+
+        return len(self._token_cache)
 
     @property
     def prev_token(self) -> Token:
-        return self.tokens[self.pos - 1]
+        return self._token_cache[self.pos - 1]
 
     def next_symbol(self):
         self.pos += 1
@@ -48,10 +69,11 @@ class Parser:
         return False
 
     def peek_several(self, *tokens_types: Tokens) -> False | list[Token]:
-        if self.pos + len(tokens_types) >= len(self.tokens):
+        desired_pos = self.pos + len(tokens_types)
+        if desired_pos >= self._fetch_until(desired_pos + 1):
             return False
 
-        toks = self.tokens[self.pos:self.pos + len(tokens_types)]
+        toks = self._token_cache[self.pos:self.pos + len(tokens_types)]
         for i, token in enumerate(toks):
             if token.kind != tokens_types[i]:
                 return False