Simplify assignment_expression?

lib/irb.rb

@@ -736,22 +736,15 @@ def inspect
     end
 
     def assignment_expression?(line)
-      # Try to parse the line and return false if it doesn't seem valid
-      s = Ripper.sexp(line)
-      return false if !s.is_a?(Array)
-
-      # The first element of the returned array should just be :program, the
-      # second element should be an array of the top level expressions
-      expressions = s[1]
-      return false if !expressions.is_a?(Array)
-
-      # We only consider the type of the last expression
-      last_expression = expressions.last
-      return false if !last_expression.is_a?(Array)
-
-      # The first element of the last expression should be its type, return
-      # whether it's one of our assignment types
-      ASSIGNMENT_NODE_TYPES.include?(last_expression[0])
+      # Try to parse the line and check if the last of possibly multiple
+      # expressions is an assignment type.
+
+      # If the expression is invalid, Ripper.sexp should return nil which will
+      # result in false being returned. Any valid expression should return an
+      # s-expression where the second selement of the top level array is an
+      # array of parsed expressions. The first element of each expression is the
+      # expression's type.
+      ASSIGNMENT_NODE_TYPES.include?(Ripper.sexp(line)&.dig(1,-1,0))
     end
 
     ATTR_TTY = "\e[%sm"