From c8e87e1d188029ca726381d191472c26b92f9fd6 Mon Sep 17 00:00:00 2001
From: Nao Pross <np@0hm.ch>
Date: Mon, 27 May 2024 15:08:47 +0200
Subject: Create poly.what_is to inspect variable that have been given names
 with poly.give_name

---
 polymatrix/__init__.py            |  2 ++
 polymatrix/expression/__init__.py | 21 ++++++++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/polymatrix/__init__.py b/polymatrix/__init__.py
index d0f53ee..b055833 100644
--- a/polymatrix/__init__.py
+++ b/polymatrix/__init__.py
@@ -27,6 +27,7 @@ from polymatrix.expression import (
     block_diag as internal_block_diag,
     lower_triangular as internal_lower_triangular,
     give_name as internal_give_name,
+    what_is as internal_what_is,
 )
 
 from polymatrix.expression.to import (
@@ -54,6 +55,7 @@ concatenate = internal_concatenate
 block_diag = internal_block_diag
 lower_triangular = internal_lower_triangular
 give_name = internal_give_name
+what_is = internal_what_is
 
 to_constant_repr = internal_to_constant
 to_matrix_repr = from_polymatrix
diff --git a/polymatrix/expression/__init__.py b/polymatrix/expression/__init__.py
index eac0a07..b44aa3e 100644
--- a/polymatrix/expression/__init__.py
+++ b/polymatrix/expression/__init__.py
@@ -7,6 +7,7 @@ import polymatrix.expression.impl
 
 from polymatrix.utils.getstacklines import get_stack_lines
 from polymatrix.expression.expression import init_expression, Expression
+from polymatrix.expression.mixins.namedexprmixin import NamedExprMixin
 
 from polymatrix.expression.init import (
     init_arange_expr,
@@ -133,4 +134,22 @@ def lower_triangular(vector: Expression):
 
 
 def give_name(expr: Expression, name: str):
-    return init_expression(init_named_expr(expr, name))
+    """ Give a name to an expression. """
+    return init_expression(init_named_expr(expr.underlying, name))
+
+
+def what_is(expr: Expression) -> Expression:
+    """
+    Opposite of :py:fn:`give_name`. Query what is inside a named expression.
+    Example:
+    .. py:
+
+        p = poly.give_name(x ** 2 + 1, "p(x)")
+        print(p) # shows "p(x)"
+        print(poly.what_is(p)) # shows "(x ** 2) + 1"
+    """
+
+    if not isinstance(expr.underlying, NamedExprMixin):
+        raise TypeError(f"{expr} is not a named expression!")
+
+    return init_expression(expr.underlying.underlying)
-- 
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