advanced-strings.md

Advanced String features

Text blocks

(do
   (def s1 """{ "fruit": "apple", "color": "red" }""")

   (def s2 """
           { 
             "fruit": "apple",
             "color": "red" 
           }
           """)

   (println s1)
   (println s2))

Interpolation

Interpolation is controlled using ~{} and ~() forms. The former is used for simple value replacement while the latter can be used to embed the results of arbitrary function invocation into the produced string.

Interpolation is implemented as a reader macro. It's parsed at read time and turned into a (str args) expression.

(do
   (let [x 100] 
      (println "x: ~{x}")
      (println "f(x): ~(inc x)")))

(do
   (let [x 100] 
      (println """x: ~{x}""")
      (println """f(x): ~(inc x)""")))

The eager parsing by the reader macro can be avoided by quoting the interpolation string, thus allow reusing it:

(do
   (def template '"y ~{y}")
   
   (defn evaluate [y] (eval template))
   
   (println (evaluate 100)) 
   (println (evaluate 200)))

(do
   (def template '"y ~(inc y)")
   
   (let [y 100] (println (eval template)))  
   (let [y 200] (println (eval template))))