Review of the Previous Lecture

Programming Languages(ICE 1341)Lecture #2February 27, 2004In-Young Koiko .AT. icu.ac.krInformation and Communications University (ICU) ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Review of the Previous Lecture • Purposes of learning programming languages • Programming domains • Programming paradigms ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Language Evaluation Criteria • Readability: How easy to read and understand programs? • Machine orientation vs. Human orientation • In the context of the problem domain • Writability: How easy to create programs for a problem domain? • In the context of the problem domain • Reliability: How easy to prevent, detect and handle errors? ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Language Evaluation Criteria – Readability Factors • Simplicity • Number of basic components • Feature Multiplicity e.g., count = count + 1; count += 1; count++; ++count • Operator Overloading e.g., int a = b + 7; float x = y + 0.7; String s = hello + “world” int[] p = new int[] { 1, 2 } + new int[] { 3, 4 } • Orthogonality:Fewer exceptions in combining primitive constructs e.g., void[] x = new void[10] • Control Statement e.g., while loop vs. goto statement • Data Types and Structures e.g., timeOut = 1 vs. timeOut = true; a record array vs. a set of arrays • Syntax Considerations • Identifier forms: e.g., length restriction, case sensitivity • Keyword selections: e.g., { } vs. Begin – End • Meaning: e.g., static variables vs. static methods in Java ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Language Evaluation Criteria – Writability Factors • Simplicity and Orthogonality • Abstraction: ability to define and use complicated structures or operations • e.g., subprograms, interfaces • Expressivity: convenience in specifying computations • e.g.1, count++ vs. count = count + 1 • e.g.2, if (a == 2 && b == 3) vs. if (a == 2 and then b == 3) • e.g.3, for vs. while ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Language Evaluation Criteria – Reliability Factors • Type Checking: testing for inconsistency in using data types • Compile-time checking is more desirable • Explicit type casting improves correctness • e.g., int a = 3 / 5 + 4 / 7 int a = (int)((float)3 / 5 + (float)4 / 7) • Exception Handling: intercepting run-time errors and performing recovery actions • Programs can continue its execution after the recovery action • Aliasing: having two or more referencing names for the same memory block • Aliasing makes programmers hard to debug programs • e.g., pointers in C • Readability and Writerbility ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Cost of a Programming Language • Cost of training programmers • Cost of writing programs • Good programming environment lowers the cost • Cost of compiling programs • Cost of executing programs • Optimization may lower the execution cost • Cost of the language implementation system (compilers and run-time platforms) • Cost of poor reliability • Unreliable languages cannot be used for developing mission-critical programs • Cost of maintaining programs • Other cost factors: portability, generality ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Imperative Languages • Languages that are designed based on the von Neumann architecture • Basic language elements: • Variables • Assignment Statements • Iteration controls * Sebesta Figure 1.1 ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Influences on Language Design • Programming methodologies • 1950s and early 1960s: Simple applications; worry about machine efficiency • Late 1960s: People efficiency became important; readability, better control structures • Structured programming • Top-down design and step-wise refinement • Late 1970s: Process-oriented to data-oriented • Data abstraction • Middle 1980s: Object-oriented programming • Middle 1990s: Component-based programming • Present: Service-oriented programming * AW Lecture Notes ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

:= id1 + id2 * id3 60 := id1 + id2 * inttoreal id3 60 Compilation Process position := initial + rate * 60 Source Program Intermediate Code Generator Lexical Analyzer temp1 := inttoreal(60) temp2 := id3 * temp1 temp3 := id2 + temp2 id1 := temp3 id1 := id2 + id3 * 60 Intermediate Code Syntax Analyzer Code Optimizer Parse Tree temp1 := id3 * 60.0 id1 := id2 + temp1 Semantic Analyzer Code Generator MOVF id3, R2 MULF #60.0, R2 MOVF id2, R1 ADDF R2, R1 MOVF R1, id1 Assembly Code * hjbang.snut.ac.kr/data/compiler/compiler_1.ppt ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Program Execution • Repetition of the fetch-execution cycle * www.faqs.org/docs/javap/c1/s1.html ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Layered View of Computer * Sebesta Figure 1.2 * AW Lecture Notes ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Pure Interpretation • Software simulation of the fetch-execution cycle • Directly execute high-level language statements • Slow process due to the decoding bottleneck • e.g., BASIC, LISP, JavaScript * Sebesta Figure 1.4 ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Hybrid Implementation Systems • Compromise between compilers and pure interpreters • Increase the portability of programs • e.g., Perl, Java ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

HW#1 • Among the programming languages described in Chapter 2, please choose 3 languages and summarize the following information about the languages: • Historic background (1-2 lines) • Programming domains • Programming paradigms • Special features • Pros and cons • Questions ICE 1341 – Programming Languages (Lecture #2) In-Young Ko

Review of the Previous Lecture