Add FileNameDrop[] (#1141)

Left to do are changes with mixed negative and positive to integer arg
values. I don't understand the behavior though.

And this isn't needed for the ChemTools loader anyway. (But ChemTools
has other bugs that still need work).

CHANGES.rst

@@ -6,6 +6,7 @@ New Builtins
 ++++++++++++
 
 * ``CheckAbort``
+* ``FileNameDrop``
 * ``SetEnvironment``
 
 ``mathics`` command line

SYMBOLS_MANIFEST.txt

@@ -399,6 +399,7 @@ System`FileFormat
 System`FileHash
 System`FileInformation
 System`FileNameDepth
+System`FileNameDrop
 System`FileNameJoin
 System`FileNameSplit
 System`FileNameTake

mathics/builtin/file_operations/file_properties.py

@@ -20,6 +20,8 @@
 from mathics.core.systemsymbols import SymbolAbsoluteTime, SymbolFailed, SymbolNone
 from mathics.eval.nevaluator import eval_N
 
+sort_order = "mathics.builtin.file-operations.file_properties"
+
 
 class FileDate(Builtin):
     """

mathics/builtin/file_operations/file_utilities.py

@@ -9,6 +9,8 @@
 from mathics.core.evaluation import Evaluation
 from mathics.core.systemsymbols import SymbolFailed
 
+sort_order = "mathics.builtin.file-operations.file_utilities"
+
 
 class FindList(Builtin):
     """

mathics/builtin/file_operations/path_operations.py

@@ -0,0 +1,103 @@
+"""
+File Path Manipulation
+"""
+
+import os.path as osp
+from pathlib import Path
+from typing import Optional
+
+from mathics.core.atoms import Integer, String
+from mathics.core.builtin import Builtin
+from mathics.core.evaluation import Evaluation
+
+# This tells documentation how to sort this module
+sort_order = "mathics.builtin.file-operations.file_path_operations"
+
+
+class FileNameDrop(Builtin):
+    """
+    <url>
+    :WMA link:
+    https://reference.wolfram.com/language/ref/FileNameDrop.html</url>
+
+    <dl>
+      <dt>'FileNameDrop["$path$", $n$]'
+      <dd>drops the first $n$ path elements in the file name $path$.
+
+      <dt>'FileNameDrop["$path$", -$n$]'
+      <dd>drops the last $n$ path elements in the file name $path$.
+
+      <dt>'FileNameDrop["$path$", {$m$, $n$}]'
+      <dd>drops elements $m$ through $n$ path elements in the file name $path$.
+
+      <dt>'FileNameDrop["$path$"]'
+      <dd>drops the last path elements in the file name $path$.
+    </dl>
+
+    >> path = FileNameJoin{"a","b","c"}
+     = ...
+
+    >> FileNameDrop[path, -1]
+      = ...
+
+    A shorthand for the above:
+
+    >> FileNameDrop[path]
+     = ...
+    """
+
+    messages = {
+        "notfinished": "m-n handling is not complete.",
+    }
+    rules = {
+        "FileNameDrop[name_]": "FileNameDrop[name, -1]",
+        "FileNameDrop[list_List, parms___]": "FileNameDrop[#1,parms]&/@list",
+    }
+    summary_text = "drop a part of a file path"
+
+    def eval_with_n(self, path: String, n: Integer, evaluation: Evaluation) -> String:
+        "FileNameDrop[path_String, n_Integer]"
+        pos = n.value
+        if pos == 0:
+            return path
+        path_elts = Path(path.value).parts
+        path_len = len(path_elts)
+        if pos >= path_len or pos <= -path_len:
+            return String("")
+
+        new_elts = path_elts[pos:] if pos > 0 else path_elts[:pos]
+        return String(osp.join(*new_elts) if new_elts else "")
+
+    def eval_with_n_to_m(
+        self, path: String, n: Integer, m: Integer, evaluation: Evaluation
+    ) -> Optional[String]:
+        "FileNameDrop[path_String, {n_Integer, m_Integer}]"
+        n_pos = n.value
+        m_pos = m.value
+        path_elts = Path(path.value).parts
+        path_len = len(path_elts)
+        if n_pos > path_len:
+            return path
+
+        if n_pos == path_len:
+            if n_pos == m_pos or n_pos + m_pos == -1:
+                # Not sure why this is so.
+                return String(osp.join(*path_elts[:-1]))
+            return path
+
+        if n_pos > m_pos:
+            return path
+
+        new_elts = None
+        if 0 < n_pos < m_pos:
+            new_elts = path_elts[: n_pos - 1] + path_elts[m_pos:]
+        elif n_pos <= m_pos <= 0:
+            new_elts = path_elts[:n_pos] + path_elts[m_pos + 1 :]
+        else:
+            evaluation.message("FindNameDrop", "notfinished")
+            return None
+
+        if new_elts:
+            return String(osp.join(*new_elts))
+        else:
+            return String("")