nested block structure: code sequences and associated declarations could be grouped into blocks without having to be turned into separate, explicitly named procedures; lexical scoping: a block could have its own private variables, procedures and functions, invisible to code outside that block, that is, information hiding. Another innovation, related to this, was in how the language was described: a mathematically exact notation, Backus–Naur form (BNF), was used to describe the language's syntax. Nearly all subsequent programming languages have used a variant of BNF to describe the context-free portion of their syntax. Algol 60 was particularly influential in the design of later languages, some of which soon became more popular. The Burroughs large systems were designed to be programmed in an extended subset of Algol. Algol's key ideas were continued, producing ALGOL 68: syntax and semantics became even more orthogonal, with anonymous routines, a recursive typing system with higher-order functions, etc.; not only the context-free part, but the full language syntax and semantics were defined formally, in terms of Van Wijngaarden grammar, a formalism designed specifically for this purpose. Algol 68's many little-used language features (for example, concurrent and parallel blocks) and its complex system of syntactic shortcuts and automatic type coercions made it unpopular with implementers and gained it a reputation of being difficult. Niklaus Wirth actually walked out of the design committee to create the simpler Pascal language. Some notable languages that were developed in this period include: 1951 – Regional Assembly Language 1952 – Autocode 1954 – IPL (forerunner to LISP) 1955 – FLOW-MATIC (led to COBOL) 1957 – FORTRAN (first compiler) 1957 – COMTRAN (precursor to COBOL) 1958 – LISP 1958 – ALGOL 58 1959 – FACT (forerunner to COBOL) 1959 – COBOL 1959 – RPG 1960 - ALGOL 60 1962 – APL 1962 – Simula 1962 – SNOBOL 1963 – CPL (forerunner to C) 1964 – Speakeasy 1964 – BASIC 1964 – PL/I 1966 – JOSS 1966 – MUMPS 1967 – BCPL (forerunner to C) 1967 - Logo (an educational language that later influenced SmallTalk and Scratch). Establishing fundamental paradigms The period from the late 1960s to the late 1970s brought a major flowering of programming languages. Most of the major language paradigms now in use were invented in this period: Speakeasy, developed in 1964 at Argonne National Laboratory (ANL) by Stanley Cohen, is an OOPS (object-oriented programming system, much like the later MATLAB, IDL and