1 files changed, 62 insertions, 0 deletions
diff --git a/macros/luatex/latex/luacas/tex/core/constantexpression.lua b/macros/luatex/latex/luacas/tex/core/constantexpression.lua
new file mode 100644
index 0000000000..0f91a037a9
--- /dev/null
+++ b/macros/luatex/latex/luacas/tex/core/constantexpression.lua
@@ -0,0 +1,62 @@
+--- @class ConstantExpression
+--- @alias Constant ConstantExpression
+--- Interface for a mathematical expression without any symbols.
+--- ConstantExpressions are AtomicExpressions by default, but individual classes may overwrite that inheritance.
+ConstantExpression = {}
+__ConstantExpression = {}
+
+----------------------
+-- Instance methods --
+----------------------
+
+
+--- @param symbol SymbolExpression
+--- @return boolean
+function ConstantExpression:freeof(symbol)
+    return true
+end
+
+--- @return boolean
+function ConstantExpression:isconstant()
+    return true
+end
+
+--- @param other Expression
+--- @return boolean
+function ConstantExpression:order(other)
+
+    -- Constants come before non-constants.
+    if not other:isconstant() then
+        return true
+    end
+
+    if self ~= E and self ~= PI and self ~= I then
+        if other ~= E and other ~= PI and other ~= I then
+            -- If both self and other are ring elements, we use the total order on the ring to sort.
+            return self < other
+        end
+        -- Special constants come after ring elements.
+        return true
+    end
+
+    -- Special constants come after ring elements.
+    if other ~= E and other ~= PI and other ~= I then
+        return false
+    end
+
+    -- Ensures E < PI < I.
+
+    if self == E then return true end
+
+    if self == I then return false end
+
+    return other == I
+end
+
+-----------------
+-- Inheritance --
+-----------------
+
+__ConstantExpression.__index = AtomicExpression
+ConstantExpression = setmetatable(ConstantExpression, __ConstantExpression)
+