4 files changed, 47 insertions, 0 deletions
diff --git a/polymatrix/expression/expression.py b/polymatrix/expression/expression.py
index 291560f..195a256 100644
--- a/polymatrix/expression/expression.py
+++ b/polymatrix/expression/expression.py
@@ -339,6 +339,7 @@ class Expression(ExpressionBaseMixin, ABC):
             ),
         )
 
+    # FIXME: replace with __setitem__?
     def set_element_at(
         self,
         row: int,
@@ -358,6 +359,9 @@ class Expression(ExpressionBaseMixin, ABC):
             ),
         )
 
+    def shape(self) -> Expression:
+        return self.copy(underlying=polymatrix.expression.init.init_shape_expr(self.underlying))
+
     # remove?
     def squeeze(
         self,
diff --git a/polymatrix/expression/impl.py b/polymatrix/expression/impl.py
index 176fe39..f4c4df4 100644
--- a/polymatrix/expression/impl.py
+++ b/polymatrix/expression/impl.py
@@ -43,6 +43,7 @@ from polymatrix.expression.mixins.quadraticmonomialsexprmixin import QuadraticMo
 from polymatrix.expression.mixins.repmatexprmixin import RepMatExprMixin
 from polymatrix.expression.mixins.reshapeexprmixin import ReshapeExprMixin
 from polymatrix.expression.mixins.setelementatexprmixin import SetElementAtExprMixin
+from polymatrix.expression.mixins.shapeexprmixin import ShapeExprMixin
 from polymatrix.expression.mixins.sliceexprmixin import SliceExprMixin
 from polymatrix.expression.mixins.squeezeexprmixin import SqueezeExprMixin
 from polymatrix.expression.mixins.subtractmonomialsexprmixin import SubtractMonomialsExprMixin
@@ -364,6 +365,14 @@ class SetElementAtExprImpl(SetElementAtExprMixin):
 
 
 @dataclassabc.dataclassabc(frozen=True)
+class ShapeExprImpl(ShapeExprMixin):
+    underlying: ExpressionBaseMixin
+
+    def __str__(self):
+        return f"shape({self.underlying})"
+
+
+@dataclassabc.dataclassabc(frozen=True)
 class SliceExprImpl(SliceExprMixin):
     underlying: ExpressionBaseMixin
     slice: tuple[int | slice | range, int | slice | range]
diff --git a/polymatrix/expression/init.py b/polymatrix/expression/init.py
index 7c3f5fa..60fa580 100644
--- a/polymatrix/expression/init.py
+++ b/polymatrix/expression/init.py
@@ -376,6 +376,10 @@ def init_set_element_at_expr(
     )
 
 
+def init_shape_expr(underlying: ExpressionBaseMixin):
+    return polymatrix.expression.impl.ShapeExprImpl(underlying)
+
+
 def init_slice_expr(
     underlying: ExpressionBaseMixin,
     slice: tuple[int | slice | range, int | slice | range]
diff --git a/polymatrix/expression/mixins/shapeexprmixin.py b/polymatrix/expression/mixins/shapeexprmixin.py
new file mode 100644
index 0000000..916289f
--- /dev/null
+++ b/polymatrix/expression/mixins/shapeexprmixin.py
@@ -0,0 +1,30 @@
+from abc import abstractmethod
+from typing_extensions import override
+
+from polymatrix.expression.mixins.expressionbasemixin import ExpressionBaseMixin
+from polymatrix.expressionstate import ExpressionState
+from polymatrix.polymatrix.abc import PolyMatrix
+from polymatrix.polymatrix.init import init_poly_matrix
+from polymatrix.polymatrix.index import PolyMatrixDict, PolyDict, MatrixIndex, MonomialIndex
+
+class ShapeExprMixin(ExpressionBaseMixin):
+    """
+    Get the shape of a polymatrix.
+    This gives the shape as a row vector [[nrows], [ncols]].
+    """
+    @property
+    @abstractmethod
+    def underlying(self) -> ExpressionBaseMixin:
+        """ The expression for which we compute the shape. """
+
+    @override
+    def apply(self, state: ExpressionState) -> tuple[ExpressionState, PolyMatrix]:
+        state, u = self.underlying.apply(state)
+        nrows, ncols = u.shape
+        p = PolyMatrixDict({
+            MatrixIndex(0, 0): PolyDict({MonomialIndex.constant(): nrows}),
+            MatrixIndex(1, 0): PolyDict({MonomialIndex.constant(): ncols})
+        })
+
+        return state, init_poly_matrix(p, shape=(2,1))
+