Introduction to Programming Languages and Compilers ..., Study notes of Programming Languages

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Introduction to Programming Languages and Compilers CS 11:00-12:00 MWF 10 Evans Notes by G. Necula, with additions by P. Hilfinger

Administrivia

• Course home page: http://www-inst.eecs.berkeley.edu/~cs
• Concurrent enrollment: see me after class
• Pick up class accounts at the end of lecture Wednesday
• Pick a partner
• We’re understaffed. Those in 10-11, 3- sections might consider moving to 9-10, 4-5; will discuss more in section meetings.

Academic Honesty

• Don’t use work from uncited sources
  • Including old code
• We use plagiarism detection software
  • 6 cases in last few semesters

PLAGIARISM

The Course Project

• Course has hidden agenda: programming design and experience.
• Substantial project in parts.
• Provides example of how complicated problem might be approached.
• Validation (testing) is part of the project.
• Also a chance to introduce important tool: version control, which we’ll use to monitor your progress
• General rule: start early!

(Short) History of High-Level Languages

• Initially, programs “hard-wired” or entered electro- mechanically: Analytical Engine, Jacquard Loom, ENIAC, punched-card-handling machines
• Programs encoded as numbers (machine language) stored as data: Manchester Mark I, EDSAC.
• 1953 IBM develops the 701
• All programming done in assembly
• Problem: Software costs exceeded hardware costs!
• John Backus: “Speedcoding”
  • An interpreter
  • Ran 10-20 times slower than hand-written assembly

FORTRAN I

• 1954 IBM develops the 704
• John Backus
  • Idea: translate high-level code to assembly
  • Many thought this impossible
• 1954-7 FORTRAN I project
• By 1958, >50% of all software is in FORTRAN
• Cut development time dramatically
  • (2 wks! 2 hrs)

After FORTRAN

• Lisp, late 1950s: dynamic, symbolic data structures.
• Algol 60: Europe’s answer to FORTRAN: modern syntax, block structure, explicit declaration. Set standard for language description. Dijkstra: “A marked improvement on its successors.”
• COBOL: late 1950’s. Business-oriented. Records.

The 60s Language Explosion

• APL (arrays), SNOBOL (strings), FORMAC (formulae), and many more.
• 1967-68: Simula 67, first “object-oriented” language.
• Algol 68: Combines FORTRAish numerical constructs, COBOLish records, pointers, all described in rigorous formalism. Remnants remain in C, but Algol68 deemed too complex.
• 1968: “Software Crisis” announced. Trend towards simpler languages: Algol W, Pascal, C

And on into the present

• Complexity increases with C++.
• Then decreases with Java.
• Then increases again (C#).
• Proliferation of little or specialized languages and scripting languages: HTML, PHP, Perl, Python, Ruby, …

Problems to address

• How to describe language clearly for programmers, precisely for implementors?
• How to implement description, and know you’re right?
  • Automatic conversion of description to implementation
  • Testing
• How to save implementation effort?
  • Multiple languages to multiple targets: can we re-use effort?
• How to make languages usable?
  • Handle errors reasonably
  • Detect questionable constructs
  • Compile quickly

Lexical Analysis

• First step: recognize letters and words.
  • Words are smallest unit above letters This is a sentence.
• Note the
  • Capital “T” (start of sentence symbol)
  • Blank “ “ (word separator)
  • Period “.” (end of sentence symbol)

More Lexical Analysis

• Lexical analysis is not trivial. Consider: ist his ase nte nce
• Plus, programming languages are typically more cryptic than English: *p->f+=-.12345e-

Parsing

• Once words are understood, the next step is to understand sentence structure
• Parsing = Diagramming Sentences
  • The diagram is a tree

Diagramming a Sentence This line is a longer sentence article noun verb article adjective noun subject object sentence