Add SymbolTable and related tests

- SymbolTable holds the addressed of different symbols, used for A-Instructions and L-Instructions
volf52 · Dec 21, 2020 · 46b3b43 · 46b3b43
1 parent 200153b
commit 46b3b43
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diff --git a/pyasm/coder.py b/pyasm/coder.py
@@ -1,4 +1,4 @@
-from typing import Dict
+from typing import Dict, Optional
 
 TranslationTable = Dict[str, str]
 
@@ -110,3 +110,73 @@ def translate_comp(mnemonic: str) -> str:
     @staticmethod
     def translate_jmp(mnemonic: str) -> str:
         return Coder.__get_mnemonic(mnemonic, Coder.__JMP, "jmp")
+
+
+class SymbolTable:
+    __RESERVED = {
+        "r0": 0,
+        "r1": 1,
+        "r2": 2,
+        "r3": 3,
+        "r4": 4,
+        "r5": 5,
+        "r6": 6,
+        "r7": 7,
+        "r8": 8,
+        "r9": 9,
+        "r10": 10,
+        "r11": 11,
+        "r12": 12,
+        "r13": 13,
+        "r14": 14,
+        "r15": 15,
+        "sp": 0,
+        "lcl": 1,
+        "arg": 2,
+        "this": 3,
+        "that": 4,
+        "screen": 16384,
+        "kbd": 24576,
+    }
+
+    __slots__ = "__lookup_table"
+
+    def __init__(self):
+        self.__lookup_table = {}
+
+    def __setitem__(self, key: str, value: int) -> None:
+        if key.lower() in SymbolTable.__RESERVED:
+            raise ValueError(f"Cannot set a reserved symbol. {key}")
+
+        self.__lookup_table[key] = value
+
+    def __getitem__(self, key: str):
+        reserved = SymbolTable.__RESERVED.get(key.lower())
+        if reserved is not None:
+            return reserved
+
+        return self.__lookup_table[key]
+
+    def get(self, key: str, default=None) -> Optional[int]:
+        reserved = SymbolTable.__RESERVED.get(key.lower())
+        if reserved is not None:
+            return reserved
+
+        return self.__lookup_table.get(key, default)
+
+    def __len__(self) -> int:
+        return len(self.__lookup_table)
+
+    def clear(self) -> None:
+        self.__lookup_table.clear()
+
+    def delete(self, symbol: str) -> bool:
+        if symbol.lower() in SymbolTable.__RESERVED:
+            return False
+
+        val = self.__lookup_table.get(symbol)
+        if val is None:
+            return False
+
+        self.__lookup_table.__delitem__(symbol)
+        return True
diff --git a/tests/test_coder.py b/tests/test_coder.py
@@ -1,6 +1,6 @@
 import pytest
 
-from pyasm.coder import Coder, InvalidMnemonicError
+from pyasm.coder import Coder, InvalidMnemonicError, SymbolTable
 
 
 def test_coder_cannot_be_instantiated():
@@ -94,3 +94,75 @@ def test_invalid_comp_(mnemonic: str):
 
     assert mnemonic in str(err.value)
     assert "comp" in str(err.value)
+
+
+@pytest.fixture(scope="module")
+def symbol_table() -> SymbolTable:
+    return SymbolTable()
+
+
+@pytest.mark.parametrize(
+    "symbol", ["r0", "R0", "THIS", "SCREEN", "scReEn", "kbd", "R7"]
+)
+def test_adding_reserved_symbols_to_symbol_table(
+    symbol_table: SymbolTable, symbol: str
+):
+    with pytest.raises(ValueError):
+        symbol_table[symbol] = 3
+
+    assert len(symbol_table) == 0
+
+
+def test_getting_reserved_symbols(symbol_table: SymbolTable):
+    for i in range(1, 15 + 1):
+        assert symbol_table.get(f"r{i}") == i
+        assert symbol_table.get(f"R{i}") == i
+
+    assert symbol_table.get("sp") == 0
+    assert symbol_table.get("SP") == 0
+    assert symbol_table.get("lcl") == 1
+    assert symbol_table.get("LCL") == 1
+    assert symbol_table.get("arg") == 2
+    assert symbol_table.get("ARG") == 2
+    assert symbol_table.get("this") == 3
+    assert symbol_table.get("THIS") == 3
+    assert symbol_table.get("that") == 4
+    assert symbol_table.get("THAT") == 4
+
+
+@pytest.mark.integ_test
+def test_setting_and_getting_symbol_table_entries_():
+    symbol_table = SymbolTable()
+
+    assert len(symbol_table) == 0
+
+    # Get from empty table
+    with pytest.raises(KeyError):
+        _ = symbol_table["abc"]
+
+    assert symbol_table.get("abc") is None
+    assert symbol_table.get("abc", default=14) == 14
+
+    assert len(symbol_table) == 0
+
+    symbol_table["loop"] = 16
+    assert symbol_table["loop"] == 16
+    assert symbol_table.get("loop") == 16
+
+    assert not symbol_table.delete("r0")
+    assert not symbol_table.delete("KBD")
+    assert not symbol_table.delete("abc")
+    assert symbol_table.delete("loop")
+    assert symbol_table.get("loop") is None
+    with pytest.raises(KeyError):
+        _ = symbol_table["loop"]
+
+    symbol_table["end"] = 256
+    assert symbol_table["end"] == 256
+    symbol_table["end"] = 147
+    assert symbol_table["end"] == 147
+    symbol_table["something_else"] = 123
+    assert len(symbol_table) == 2
+
+    symbol_table.clear()
+    assert len(symbol_table) == 0