Exercise 3: Work with text

Aim: distinguish a name from literal text, use escapes and qualify a library function. Save ex03.fib.

Type and predict

(ns main (:require [fib.string :as text]))
(defun main () -> i64
  (let ((name "Ada")
        (cups 3))
    (do
      (println (str "Hello, " name "."))
      (println (str name " has " cups " cups."))
      (println "She said \"hello\".")
      (println (text/join " / " ["tea" "coffee" "water"]))
      0)))

str builds text from its arguments. \" puts a quote inside a string without ending it. The namespace declaration gives fib.string the alias text; text/join joins strings with a separator. Unqualified join has a different job: waiting for a task. Keep this string call qualified.

Check your prediction

Hello, Ada.
Ada has 3 cups.
She said "hello".
tea / coffee / water
0

Change it

1. Change the name and number without editing the message templates.
2. Print a string containing \n. Predict the number of output lines.
3. Join the same drinks with ", ", then an empty separator.

Break and repair

Remove the backslash before an interior quote in a copy. Observe how the reader now sees the rest of the line. Restore the escape. Then misspell the text alias on the join call and repair the namespace/call agreement.

Checkpoint

Explain the difference between name and "name". Build a greeting with a different alias for fib.string, and explain why both declarations and calls must agree. Reference: module names.

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