postponing unquote

I need to generate S-expressions like:

(let ((val "datum")) val)

The actual expressions are more complex, the value “datum” is dynamic, therefore the special Scheme feature “quasiquote” should be used:

(quasiquote (let ((val ,value)) val))

When a Scheme imterpreter/compiler finds a “quasiquote” construction, it replaces comma-starting identifiers with their values.

To add more complexity, I have to generate the skeleton of an S-expression at one time, and provide actual values later. Surprisingly for me, I needed only one attempt to write a working test code:

(define (pre-generate)
  (lambda (value)
    (quasiquote
      (let ((val ,value))
        val))))

(define x (pre-generate))
(write x)
(display "\n")
(define y (x "datum"))
(write y)
(display "\n")

Executing code in Guile:


#
(let ((val "datum")) val)

In Bigloo:


#
(let ((val "datum")) val)

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