> They thought many ideas of it (see Lisp, Smalltalk) but computers where not powerful enough for complex compilers. That's probably true for borrower-checking

> They thought many ideas of it (see Lisp, Smalltalk) but computers where not powerful enough for complex compilers. That's probably true for borrower-checking specifically, but I don't think it accounts for all language-design breakthroughs. There were decades between the development of functional programming languages, and widespread hybrid languages which incorporated those ideas (e.g. modern Python and C#).