Initial commit

json_py/parser.py

@@ -0,0 +1,73 @@
+from __future__ import annotations
+import typing
+import json_py.lexer as lexer
+
+ParserResult = typing.Tuple[typing.Any, lexer.TokenList]
+
+
+def parse_array(tokens: lexer.TokenList) -> ParserResult:
+    json_array: typing.List[typing.Any] = []
+
+    if tokens[0] == "]":
+        return json_array, tokens[1:]
+
+    expect_comma = False
+    for i in range(len(tokens)):
+        t = tokens[i]
+        if t == "]":
+            if not expect_comma:
+                raise ValueError("Expected one more item")
+
+            return json_array, tokens[i + 1 :]
+        elif t == ",":
+            if not expect_comma:
+                raise ValueError("Unexpected comma")
+
+            expect_comma = False
+        else:
+            if expect_comma:
+                raise ValueError("Expected comma but got item")
+
+            json_array.append(t)
+            expect_comma = True
+
+    raise ValueError("List not closed")
+
+
+def parse_object(tokens: lexer.TokenList) -> ParserResult:
+    json_object: typing.Any = {}
+
+    if tokens[0] == "}":
+        return json_object, tokens[1:]
+
+    is_syntax: typing.Callable[[str], bool] = lambda x: str(x) in ":"
+    while True:
+        json_key = tokens[0]
+
+        if is_syntax(json_key):
+            raise Exception(f"Expected value before '{json_key}'")
+
+        colon = tokens[1]
+        if colon != ":":
+            raise Exception(f"Expected ':' but got '{colon}'")
+
+        json_value, tokens = parse(tokens[2:])
+        json_object[json_key] = json_value
+
+        next_token = tokens[0]
+        if next_token == ",":
+            tokens = tokens[1:]
+        elif next_token == "}":
+            return json_object, tokens[1:]
+        else:
+            raise Exception(f"Expected ',' or '{'}'}' but got '{next_token}'")
+
+
+def parse(tokens: lexer.TokenList) -> typing.Any:
+    t = tokens[0]
+    if t == "[":
+        return parse_array(tokens[1:])
+    elif t == "{":
+        return parse_object(tokens[1:])
+    else:
+        return t, tokens[1:]