* guix/utils.scm (define-record-type*)[make-syntactic-constructor]: Add
a `thunked' parameter.
(thunked-field?, field-bindings): New procedures. Use the latter when
generating `letrec*' bindings.
[thunked-field?, thunked-field-accessor-name, field-spec->srfi-9,
thunked-field-accessor-name]: New procedures.
Use them when generating the `define-record-type' form, and to
generated thunk field accessors, along call to
`make-syntactic-constructor' with the new argument.
* tests/utils.scm ("define-record-type* & thunked",
"define-record-type* & thunked & default",
"define-record-type* & thunked & inherited"): New tests.
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