On Sun, Jun 07, 2020 at 08:09:40PM +0800, Siyuan Chen wrote:
> There is an alternative of Lisp macros called FEXPRs, see
> https://en.wikipedia.org/wiki/Macro_(computer_science)#Early_Lisp_macros
> > Early Lisp macros
> > Before Lisp had macros, it had so-called FEXPRs, function-like operators
> whose inputs were not the values computed by the arguments but rather the
> syntactic forms of the arguments, and whose output were values to be used
> in the computation. In other words, FEXPRs were implemented at the same
> level as EVAL, and provided a window into the meta-evaluation layer. This
> was generally found to be a difficult model to reason about effectively.

This wasn't just a feature for the expert user; it was the way basic 
primitives like 'quote', 'cond', and 'let' were implemented in the 
lisp 1.5 interpreter; the actual interpreting code being written in 
assembler (or Lisp, if it wasn't an utterly necessary primitive).

-- hendrik

> More information, see https://en.wikipedia.org/wiki/Fexpr

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