Why are most S-Expression languages dynamically typed?

Question

How come most Lisps and Schemes are dynamically typed? Does static typing not mix with some of their common features?

Answer 1

When Lisp was invented in the years from 1958 to 1960 it introduced a lot of features both as a language and an implementation (garbage collection, a self-hosting compiler, ...). Some features were inherited (with some improvements) from other languages (list processing, ...). The language implemented computation with functions. The s-expressions were more an implementation detail ( at that time ), than a language feature. A type system was not part of the language. Using the language in an interactive way was also an early implementation feature.

The useful type systems for functional languages were not yet invented at that time. Still until today it is also relatively difficult to use statically typed languages in an interactive way. There are many implementations of statically typed languages which also provide some interactive interface - but mostly they don't offer the same level of support of interactive use as a typical Lisp system. Programming in an interactive Lisp system means that many things can be changed on the fly and it could be problematic if type changes had to be propagated through whole programs and data in such an interactive Lisp system. note that Some Schemers have a different view about these things. R6RS is mostly a batch language generally not that much in the spirit of Lisp...

The functional languages that got invented later with static type systems then also got a non-s-expression syntax - they did not offer support for macros or related features. later some of these languages/implementations used a preprocessor for syntactic extensions.