**Classic Languages

*Criteria:

• Widely used in production today
• Withstood the test of time (created 30+ years ago)

SQL

• Appeared: 1974
• Ranked 9th on (TIOBE Index)[https://www.tiobe.com/tiobe-index/], February 2020

• .s - Show the stack
• +, -, *, mod - Math operators
• /mod - performs both / and mod

• drop and 2drop - drop a stack item (once / twice)
• dup - duplicate a stack item
• rot - rotate the stack