CS 331, Principles of Programming LanguagesChapter 1

ObjectivesTo introduce several different paradigms of programmingTo gain experience with these paradigms by using example programming languagesTo understand concepts of syntax, translation, abstraction, and implementation

Paradigms of Programming?There are several ways to think about computation:set of instructions to be followedset of expressions to be evaluateda set of rules to be applieda set of objects to be rearrangeda set of messages to be sent and received

Some Programming ParadigmsProceduralexamples: C, Pascal, Basic, FortranFunctionalexamples: Lisp, MLObject-orientedexamples: C++, Java, SmalltalkRule-based (or Logic)example: Prolog

Why so many?Most important: the choice of paradigm (and therefore language) depends on how humans best think about the problemOther considerations:efficiencycompatibility with existing codeavailability of translators

Models of ComputationRAM machineproceduralDirected Acyclic GraphsSmalltalk model of O-Opartial recursive functionsLisp and MLMarkov algorithmsProlog is loosely based on these

Lots of LanguagesThere are many programming languages out thereLots of other PL-like objectsdocument languages, e.g. LaTeX, Postscriptcommand languages, e.g. csh, MATLABMarkup languages, e.g. HTML and XMLspecification languages, e.g. Z, UML

TranslationCompilationTranslate into instructions suitable for some other (lower level) machineDuring execution, that machine maintains program state informationInterpretationMay involve some translationInterpreter maintains program state

Trade-offsCompilationlower level machine may be faster, so programs run fastercompilation can be expensiveexamples: C (and Java?)Interpretationmore ability to perform diagnostics (or changes) at run-timeexamples: Basic, UNIX shells, Lisp

Web resourcesProgramming language researchhttp://www.cs.cmu.edu/afs/cs.cmu.edu/user/mleone/web/language-research.htmlFree compilers and interpretershttp://cuiwww.unige.ch/OSG/info/FreeComp/fc/categorie.html