CS3: Introduction to Symbolic Programming

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CS3 Introduction to Symbolic Programming

• Instructor Nate Titterton
• Email nate_at_socrates.berkeley.edu

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Announcements

• Nate's office hours
• Wed 2-4
• 329 Soda
• Get your card keys

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Any questions?

• Grading?
• Working at home?

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Review

• What is Scheme?
• (interpreter, editor)
• Functions
• Words and Sentences

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Some programming

• first-two
• takes a word, returns the first two letters (as a
  word)
• two-first
• takes a sentence of two words, returns the first
  two letters (as a word)

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A big idea

• Data abstraction
• Selectors!
• Constructors!

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Coming up conditionals

• Conditionals allow programs to do different
  things depending on data values
• To make decisions
• "Intelligence" depends on this

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Structure of conditionals

• (if lttrue? or false?gt ltdo something if
  truegt ltdo something if falsegt)
• (define (smarty x)
• (if (odd? x)
• (se x '(is odd))
• (se x '(is even))))

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true? or false? Boolean!

• With conditionals, we need something that
  represents TRUE and FALSE.
• t and f
• in practice, everything is true except f
• false is true!
• (really, false is t)
• Predicates procedures that return t or f
• by convention, their names end with a "?"