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Lecture 28: More on Functional Programming

The University of North Carolina at Chapel Hill. Lecture 28: More on Functional Programming. COMP 144 Programming Language Concepts Spring 2002. Felix Hernandez-Campos April 1. Advanced Functional Programming. Functional programming languages can increase readability

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Lecture 28: More on Functional Programming

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  1. The University of North Carolina at Chapel Hill Lecture 28: More on Functional Programming COMP 144 Programming Language Concepts Spring 2002 Felix Hernandez-Campos April 1 COMP 144 Programming Language Concepts Felix Hernandez-Campos

  2. Advanced Functional Programming • Functional programming languages can increase readability • But they can also help developing obfuscated code • Unlambda is a functional programming language specifically designed for this task • It is powerful (Turing-complete) • It is the ideal language for abstraction-elimination COMP 144 Programming Language Concepts Felix Hernandez-Campos

  3. Programming Principles • Seven primitive functions : • k, • s, • i, • v, • d, • C, and • .x COMP 144 Programming Language Concepts Felix Hernandez-Campos

  4. Numbers • Church integers: • <0> is ^f^x$x (i.e. `ki). • <1> is ^f^x`$f$x (i.e. i). • <2> is ^f^x`$f`$f$x (i.e. ``s``s`kski). • <3> is ^f^x`$f`$f`$f$x (i.e. ``s``s`ksk``s``s`kski). • and so on… COMP 144 Programming Language Concepts Felix Hernandez-Campos

  5. Example: Fibonacci • The following Unlambda program calculates and prints the Fibonacci numbers (as lines of asterisks) ```s``s``sii``s`kk`ki`ki``s``s`ks``s``s`ks``s`kk`ks``s``s`ks``s``s`ks` `s`kk`ks``s``s`ks``s``s`ks``s`kk`ks``s``s`ks``s``s`ks``s`kk`ks``s``s`k s``s`kk`kk``s`kk`kr``s``s`ks``s``s`ks``s`kk`ks``s``s`ks``s``s`ks``s`kk `ks``s``s`ks``s`kk`kk`ki``s``s`ks``s`kk`kk``s`kk`k.*``s``s`ks``s`kk`kk ``s`kki``s``s`ks``s`kk`kk``s`kki``s`kk`ki``s``s`ks``s``s`ks``s`kk`ks`` s``s`ks``s``s`ks``s`kk`ks``s``s`ks``s`kk`kk``s`kk`k``s``s`ks``s``s`ks` `s`kk`ks``s``s`ks``s``s`ks``s`kk`ks``s``s`ks``s`kk`kk``s`kk`ks``s``s`k s``s``s`ks``s`kk`ks``s``s`ks``s``s`ks``s`kk`ks``s``s`ks``s`kk`kk``s`kk `ks``s``s`ks``s``s`ks``s`kk`ks``s``s`ks``s`kk`kk``s`kk`kk``s``s`ks``s` kk`kk``s`kki``s``s`ks``s``s`ks``s`kk`ks``s``s`ks``s`kk`kk``s`kk`kk``s` kk`ki``s``s`ks``s``s`ks``s`kk`ks``s``s`ks``s``s`ks``s`kk`ks``s``s`ks`` s`kk`kk``s`kk`ks``s``s`ks``s``s`ks``s`kk`ks``s``s`ks``s``s`ks``s`kk`ks ``s``s`ks``s`kk`kk``s`kk`ks``s``s`ks``s``s`ks``s`kk`ks``s``s`ks``s`kk` kk``s`kk`kk``s``s`ks``s`kk`kk`ki``s``s`ks``s``s`ks``s`kk`ks``s``s`ks`` s`kk`kk``s`kk`kk``s`kk`ki``s``s`ks``s`kk`kk``s`kk`ki``s``s`ks``s`kk`kk `ki``s`kk`ki COMP 144 Programming Language Concepts Felix Hernandez-Campos

  6. Unlambda in Unlambda • http://www.ofb.net/~jlm/unlambda/unlambda.unl.gz COMP 144 Programming Language Concepts Felix Hernandez-Campos

  7. The Shocking Truth • “It's disgusting — it's revolting — we love it.” CyberTabloid • “Unlambda, the language in which every program is an IOUCC.” Encyclopædia Internetica • “The worst thing to befall us since Intercal.” Computer Languages Today • “The effect of reading an Unlambda program is like habing your brains smashed out by a Lisp sexp wrapped around an ENIAC. You won't find anything like it west of Alpha Centauri.” The Hitch-Hacker's Guide to Programming COMP 144 Programming Language Concepts Felix Hernandez-Campos

  8. Source of this evil • Reference • http://www.eleves.ens.fr:8080/home/madore/programs/unlambda/ • Extra credit • A+ guaranteed to the first one that develops a Turtle interpreter in Unlambda COMP 144 Programming Language Concepts Felix Hernandez-Campos

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