Merge pull request #1242 from mathics/fixReadExpression

Processing comments in Read Expression

Author: mmatera

mathics/builtin/files.py

@@ -34,6 +34,7 @@
 from mathics.core.expression import (
     BoxError,
     Complex,
+    BaseExpression,
     Expression,
     Integer,
     MachineReal,
@@ -624,6 +625,14 @@ class Read(Builtin):
     ## #> str = Quiet[StringToStream["Sin[1 123"]; Read[str, Expression]]
     ##  = $Failed
 
+    ## HoldExpression:
+    >> str = StringToStream["2+2\\n2+3"];
+    >> Read[str, Hold[Expression]]
+     = Hold[2 + 2]
+    >> Read[str, Expression]
+     = 5
+    >> Close[str];
+
     ## Multiple types
     >> str = StringToStream["123 abc"];
     >> Read[str, {Number, Word}]
@@ -766,8 +775,15 @@ def apply(self, channel, types, evaluation, options):
         else:
             types = (types,)
 
+        # TODO: look for a better implementation handling "Hold[Expression]".
+        #
         types = (
-            typ._leaves[0] if typ.get_head_name() == "System`Hold" else typ
+            Symbol("HoldExpression")
+            if (
+                typ.get_head_name() == "System`Hold"
+                and typ.leaves[0].get_name() == "System`Expression"
+            )
+            else typ
             for typ in types
         )
         types = Expression("List", *types)
@@ -778,6 +794,7 @@ def apply(self, channel, types, evaluation, options):
                 "Byte",
                 "Character",
                 "Expression",
+                "HoldExpression",
                 "Number",
                 "Real",
                 "Record",
@@ -875,7 +892,7 @@ def reader(stream, word_separators, accepted=None):
                     if tmp == "":
                         raise EOFError
                     result.append(tmp)
-                elif typ == Symbol("Expression"):
+                elif typ == Symbol("Expression") or typ == Symbol("HoldExpression"):
                     tmp = next(read_record)
                     while True:
                         try:
@@ -889,13 +906,17 @@ def reader(stream, word_separators, accepted=None):
                             except EOFError:
                                 expr = Symbol("EndOfFile")
                                 break
+                        except Exception as e:
+                            print(e)
 
-                    if expr is None:
+                    if expr == Symbol("EndOfFile"):
                         evaluation.message(
                             "Read", "readt", tmp, Expression("InputSteam", name, n)
                         )
                         return SymbolFailed
-                    else:
+                    elif isinstance(expr, BaseExpression):
+                        if typ == Symbol("HoldExpression"):
+                            expr = Expression("Hold", expr)
                         result.append(expr)
 
                 elif typ == Symbol("Number"):
@@ -3815,10 +3836,13 @@ class Compress(Builtin):
 
     def apply(self, expr, evaluation, options):
         "Compress[expr_, OptionsPattern[Compress]]"
-        string = expr.format(evaluation, "System`FullForm")
-        string = string.boxes_to_text(
-            evaluation=evaluation, show_string_characters=True
-        )
+        if isinstance(expr, String):
+            string = '"' + expr.value + '"'
+        else:
+            string = expr.format(evaluation, "System`FullForm")
+            string = string.boxes_to_text(
+                evaluation=evaluation, show_string_characters=True
+            )
         string = string.encode("utf-8")
 
         # TODO Implement other Methods