Why Early BASIC Interpreters Were Not Structured

Early BASIC interpreters were not structured mainly due to their foundation on versions of Dartmouth BASIC built before 1976, where modern structuring keywords were scarce or non-existent. This article delves into the historical context and technological limitations that contributed to this lack of structure in early BASIC interpreters.

The Role of Dartmouth BASIC

The earliest versions of BASIC, up to version 5, did not adopt modern structuring techniques. The first five versions of Dartmouth BASIC did not contain contemporary structure-oriented keywords, making it more difficult to develop programs with organized and efficient code.

However, the SBASIC preprocessor introduced in 1976 aimed to address this issue. It added necessary structuring elements to enhance the language. Unfortunately, versions 6 and 7, which integrated the SBASIC preprocessor into the compiler, did not gain the same level of recognition as the earlier, more stable versions of BASIC (like version 5).

Why Most Interpreters Lacked Structure

The absence of structured programming in early BASIC interpreters can be attributed to several factors:

Technological Constraints

Cost and Storage Space: During the late 1970s and early 1980s, cost and storage space considerations outweighed the benefits of advanced programming techniques. CPUs with 16-bit address buses and limited RAM made it challenging to incorporate modern programming constructs. Machine Specifications: The machines available at the time were quite basic. For example, the first microcomputer BASIC supported by the author had just 1k of RAM expandable to 16k, with an 8k ROM that held the interpreter along with a rudimentary operating system. Hardware Limitations: The absence of dedicated graphics hardware and the CPU's necessity to refresh the display meant that additional space would be required, further reducing the space available for code. Speed Limitations: The processor's performance was constrained, making the overhead of control structures, such as procedure calls and argument passing, even more significant.

Cultural Factors

The people designing these machines were often hobbyists and inventors, not primarily involved in academic Computer Science. They were often disconnected from the academic pursuit of efficient programming techniques. Concepts like structured programming and the avoidance of GOTO statements, which were gaining traction in research, did not yet have practical implementations due to technological and cultural limitations.

Additionally, efforts to optimize hardware for more efficient Lisp code compared to standard minicomputers were less successful and did not influence the widespread adoption of structured programming in BASIC.

Consequences for Early Users

The lack of structured programming in early BASIC interpreters meant that code was often harder to read, maintain, and debug. Programmers had to rely on a more procedural approach, which, while functional, could lead to less efficient and less readable code.

However, despite these limitations, BASIC became the de facto language for early microcomputers due to its simplicity and popularity. Bill Gates recognized its potential, and his efforts in promoting and developing BASIC for personal computers further cemented its significance.

In conclusion, the reasons why early BASIC interpreters were not structured are multifaceted, involving both technological and cultural factors. However, as technology has advanced, modern versions of BASIC, with their structured programming capabilities, have become more widely available and more user-friendly.