all tasks

Task/Variables/GAP/variables.gap

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+# At top level, global variables are declared when they are assigned, so one only writes
+global_var := 1;
+
+# In a function, local variables are declared like this
+func := function(n)
+    local a;
+    a := n*n;
+    return n + a;
+end;
+
+# One can test whether a variable is assigned
+IsBound(global_var);
+# true;
+
+# And destroy a variable
+Unbind(global_var);
+
+# This works with list elements too
+u := [11, 12, , 14];
+IsBound(u[4]);
+# true
+IsBound(u[3]);
+# false
+Unbind(u[4]);