Many people have their problems with lispy s-expressions because
they involve many parentheses. Especially if Lisp is coded in
the way it should, “like a waterfall”, that is: functional,
reusing values, avoiding sequences. Then code often looks like
this (example taken from
(defparameter *t* (make-array 64 :element-type 'ub32 :initial-contents (loop for i from 1 to 64 collect (truncate (* 4294967296 (abs (sin (float i 0.0d0))))))))
Note the 9(!) closing parens at the end; these become difficult to maintain, especially if code gets changed in the middle of it.
(f (g (h x)))
(f ~ g ~ h x)
Notice the reduction of parentheses. Again the first sample:
(defparameter *t* ~ make-array 64 :element-type 'ub32 :initial-contents ~ loop for i from 1 to 64 collect ~ truncate ~ * 4294967296 ~ abs ~ sin ~ float i 0.0d0)
Suddenly, we have much less parentheses, but a more mysterious and—at least to Lisp users—more weird syntax.
Also note that there have been former tries to simplify multiple
parentheses, for example the superparentheses of Interlisp. They are
] closes all parens upto the first
or to toplevel.
Or, as we can read in the INTERLISP Manual:
The INTERLISP read program treats square brackets as “superparentheses”: a right square bracket automatically supplies enough right parentheses to match back of the last left square bracket (in the expression being read), or if none has appeared, to match the first left parentheses, […]
Now the code would get:
(defparameter *t* (make-array 64 :element-type 'ub32 :initial-contents (loop for i from 1 to 64 collect (truncate (* 4294967296 (abs (sin (float i 0.0d0]
This looks even more weird than the
~-syntax because it is visibly
unbalanced. This is probably the main reason that the superparentheses
didn’t made it into Common Lisp.
I, for myself, however consider the
~-syntax to be an interesting,
refreshing idea for lisp and hope Paul Graham will implement them.
If not in the core language, they are at least possible using a reader
extension. Maybe I code them for myself in Common Lisp. Mhmmm…