add make-variable

from syntax-objects/Summer2021#8
cc @xgqt

index.scrbl

@@ -18,6 +18,7 @@
 
 @include-example{first-class-or}
 @include-example{optional-assert}
+@include-example{make-variable}
 @include-example{cross-macro-communication}
 @include-example{let-star}
 @include-example{while-break}

make-variable/make-variable-test.rkt

@@ -0,0 +1,12 @@
+#lang racket/base
+(module+ test
+  (require rackunit syntax-parse-example/make-variable/make-variable)
+
+  (test-case "make-variable"
+    (check-equal?
+      (make-variable "this_variable_will_probably_change")
+      "this_variable_will_probably_change=\"this_variable_will_probably_change\"")
+    (define Z "Zzz...")
+    (check-equal? (make-variable Z) "Z=\"Zzz...\""))
+
+)

make-variable/make-variable.rkt

@@ -0,0 +1,16 @@
+#lang racket/base
+(provide make-variable as-variable)
+(require (for-syntax racket/base syntax/parse))
+
+(define (as-variable lhs rhs)
+  (format "~a=\"~a\"" lhs rhs))
+
+(define-syntax (make-variable stx)
+  (syntax-parse stx
+    [(_ name:id)
+     #'(as-variable (symbol->string 'name) name)]
+    [(_ str:string)
+     #'(as-variable str str)]
+    [(_ ((~literal quote) sym))
+     #'(as-variable (symbol->string 'sym) 'sym)]))
+

make-variable/make-variable.scrbl

@@ -0,0 +1,38 @@
+#lang syntax-parse-example
+@require[
+  (for-label racket/base racket/contract syntax/parse syntax-parse-example/make-variable/make-variable)]
+
+@(define make-variable-eval
+   (make-base-eval '(require syntax-parse-example/make-variable/make-variable)))
+
+@title{@tt{make-variable}}
+@stxbee2021["xgqt" 8]
+@nested[#:style 'inset @emph{Adapted from the @hyperlink["https://gitlab.com/xgqt/racket-ebuild" @tt{racket-ebuild}] project.}]
+
+@; =============================================================================
+
+@defmodule[syntax-parse-example/make-variable/make-variable]{}
+
+@defform[(make-variable v)]{
+  Formats a variable declaration for POSIX shell scripts.
+  @itemlist[
+    @item{When given a string or symbol, the input is the name and value of the new variable.}
+    @item{When given an identifier, the identifier name is the variable name and the identifier value is the variable's value.}
+  ]
+
+  @examples[#:eval make-variable-eval
+    (make-variable "this_variable_will_probably_change")
+    (define Z "Zzz...")
+    (make-variable Z)
+  ]
+
+  The macro uses @racket[syntax-parse] to decide how to process its input.
+  It then outputs code that calls the @racket[as-variable] helper function.
+
+  @racketfile{make-variable.rkt}
+
+}
+
+@defproc[(as-variable [lhs any/c] [rhs any/c]) string?]{
+  Formats two values into a POSIX variable declaration.
+}