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GC16/3011 Functional Programming Lecture 4 Miranda

GC16/3011 Functional Programming Lecture 4 Miranda. (and her friend Amanda). Contents. Miranda/Amanda Amanda demonstration Comments Legal names and binding Types and type checking Tuples Simple functions. Amanda. PC version of Miranda Almost (but not quite) the same!

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GC16/3011 Functional Programming Lecture 4 Miranda

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  1. GC16/3011 Functional ProgrammingLecture 4Miranda (and her friend Amanda)

  2. Contents • Miranda/Amanda • Amanda demonstration • Comments • Legal names and binding • Types and type checking • Tuples • Simple functions

  3. Amanda • PC version of Miranda • Almost (but not quite) the same! • Get it from the Web pages • http://www.cs.ucl.ac.uk/teaching/3C11/index.html • Amanda204: • http://www.engineering.tech.nhl.nl/engineering/personeel/bruin/data/amanda204.zip

  4. Amanda Demonstration • Lambda Calculus • (3 + 4) * (6 + 7) • But you can gives names to (sub)expressions • x = 3 + 4 • y = 6 + 7 • main = (x * y) • Also give names to functions (no lambdas!) • inc x = x + 1 • main = inc 56

  5. Amanda Demonstration • Interpretive environment • Use it as a calculator • Simple definitions stored in a file • Main definition • Define and use functions

  6. Comments • VERY important! • Use them from the start • Example: || a simple definition for some text: message = “hello mum” || here is a function which adds one to a number: inc x = x + 1

  7. Legal names • BINDING: • NAME = EXPRESSION • Funcname argname = EXPRESSION • Binds funcname when defined (static) • Binds argname when applied to an argument (dynamic) • Each binding is unique, within specified scope • Scope of argname is the function body (only) • Nested scopes (see later) permit nested bindings for same name • Names MUST start with an alphabetic character • Names MUST NOT start with a capital letter! • but may contain numbers and underscores

  8. Types • Data can be, for example: • Numbers (42): num • Characters (‘A’): char • Text (“strings”): [char] • Truth values (True, False): bool • Functions (f x = x + 1): arg_type -> result_type • Miranda/Amanda allows us to CATEGORISE data into specific types • Helps organise programs better • Helps detect errors

  9. Type Checking • Done before the program is run • Checks that operators (e.g. +) are executed on data of the correct type • Checks that functions are applied to data of the correct type • You can ask “what type is this?” • You can specify “this is a Boolean value” etc.

  10. Tuples • A simple data structure • (“Sheila Bloggs”, 23, “2 Turnabout Road, NW3”, 60, False) • (34, True) :: (num, bool) • (34, True) DOES NOT EQUAL (True, 34) • (“increment”, (+ 1), inc) :: ([char], num->num, num->num)

  11. Simple Functions inc x = x + 1 || the hello function hello :: num -> [char] hello x = “good morning”, if (x<10) = “goodbye”, otherwise

  12. Summary • Miranda/Amanda • Amanda demonstration • Comments • Legal names and binding • Types and type checking • Tuples • Simple functions

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