Re: Spacing grobs with an invisible object between them (hack)

[Aaron Hill]

On 2020-02-06 6:10 am, Paolo Prete wrote:
> (code)

A few comments on the code:

1) "begin" is used to specify multiple expressions in a construct that 
only accepts one.  "if" would be an example where "begin" could be 
useful; but "let", like many other constructs, already accepts a list of 
expressions to evaluate.

;;;;
(define (foo a)
  (let ((b (1+ a)))
    (begin
      (do-something a)
      (do-something b))))

;; ...would become...

(define (foo a)
  (let ((b (1+ a)))
    (do-something a)
    (do-something b)))
;;;;


2) "let" without any bindings would be superfluous syntax.

;;;;
(define (foo a)
  (let ()
    (do-something a)))

;; ...would become...

(define (foo a)
  (do-something a))
;;;;


3) "cond" is best used when there are more than two paths, otherwise 
"if" is more concise.

;;;;
(define (foo a)
  (cond ((< 0 a) (do-something a))
        (else (do-another-thing a))))

;; ...would become...

(define (foo a)
  (if (< 0 a) (do-something a)
              (do-another-thing a)))
;;;;


4) ly:dir? and symbol-list? are built-in type predicates useful for 
directions and grob paths, respectively.  These can replace your current 
use of strings as inputs, which eliminates some potentially unsightly 
quotation marks in the user code.


5) Event functions let the user specify direction with the normal syntax 
(^, -, _), potentially obviating the need for a direction argument:

%%%%
\version "2.19.83"
foo = #(define-event-function (color) (color?)
  #{ -\tweak color #color -\markup "foo" #})
{ b'4 ^\foo #red b'4 _\foo #blue }
%%%%


-- Aaron Hill