【文章內容簡介】 OL 60 Evaluation (continued) ? Failure – Never widely used, especially in . – Reasons ?Lack of I/O and the character set made programs nonportable ?Too flexiblehard to implement ?Entrenchment of Fortran ?Formal syntax description ?Lack of support from IBM 134 Computerizing Business Records: COBOL ? Environment of development – UNIVAC was beginning to use FLOWMATIC – USAF was beginning to use AIMACO – IBM was developing COMTRAN 135 COBOL Historical Background ? Based on FLOWMATIC ? FLOWMATIC features – Names up to 12 characters, with embedded hyphens – English names for arithmetic operators (no arithmetic expressions) – Data and code were pletely separate – The first word in every statement was a verb 136 COBOL Design Process ? First Design Meeting (Pentagon) May 1959 ? Design goals – Must look like simple English – Must be easy to use, even if that means it will be less powerful – Must broaden the base of puter users – Must not be biased by current piler problems ? Design mittee members were all from puter manufacturers and DoD branches ? Design Problems: arithmetic expressions? subscripts? Fights among manufacturers 137 COBOL Evaluation ? Contributions – First macro facility in a highlevel language – Hierarchical data structures (records) – Nested selection statements – Long names (up to 30 characters), with hyphens – Separate data division 138 COBOL: DoD Influence ? First language required by DoD – would have failed without DoD ? Still the most widely used business applications language 139 The Beginning of Timesharing: BASIC ? Designed by Kemeny amp。 Kurtz at Dartmouth ? Design Goals: – Easy to learn and use for nonscience students – Must be ―pleasant and friendly‖ – Fast turnaround for homework – Free and private access – User time is more important than puter time ? Current popular dialect: Visual BASIC ? First widely used language with time sharing （分時性，多人使用同一臺計算機） 140 Everything for Everybody: PL/I ? Designed by IBM and SHARE ? Computing situation in 1964 (IBM39。s point of view) – Scientific puting ?IBM 1620 and 7090 puters ?FORTRAN ?SHARE user group – Business puting ?IBM 1401, 7080 puters ?COBOL ?GUIDE user group 141 PL/I: Background ? By 1963 – Scientific users began to need more elaborate I/O, like COBOL had。 business users began to need floating point and arrays for MIS – It looked like many shops would begin to need two kinds of puters, languages, and support stafftoo costly ? The obvious solution – Build a new puter to do both kinds of applications – Design a new language to do both kinds of applications 142 PL/I: Design Process ? Designed in five months by the 3 X 3 Committee – Three members from IBM, three members from SHARE ? Initial concept – An extension of Fortran IV ? Initially called NPL (New Programming Language) ? Name changed to PL/I in 1965 143 PL/I: Evaluation ? PL/I contributions – First unitlevel concurrency – First exception handling – Switchselectable recursion – First pointer data type – First array cross sections ? Concerns – Many new features were poorly designed – Too large and too plex 144 Two Early Dynamic Languages: APL and SNOBOL ? Characterized by dynamic typing and dynamic storage allocation ? Variables are untyped – A variable acquires a type when it is assigned a value ? Storage is allocated to a variable when it is assigned a value 145 APL: A Programming Language ? Designed as a hardware description language at IBM by Ken Iverson around 1960 – Highly expressive (many operators, for both scalars and arrays of various dimensions) – Programs are very difficult to read ? Still in use。 minimal changes 146 SNOBOL（ String Orientated Symbolic Language） ? Designed as a string manipulation language at Bell Labs by Farber, Gr