Exercise 1: Read a program aloud

Aim: identify forms, strings and comments. Save the program as ex01.fib. Run each exercise with fibc run exNN.fib, substituting its number.

Type and predict

;; A semicolon starts a comment; this line does not print.
(defun main () -> i64
  (do
    (println "one form")
    (println "two forms")
    (println "a ; inside a string is text")
    0))

Read (println "one form") as “call println with this string.” Parentheses group a form; the first item names the operation. Double quotes delimit a string. defun defines a function, and () is main's empty parameter list. -> i64 declares its result type. do evaluates its forms in order and returns the last.

Check your prediction

one form
two forms
a ; inside a string is text
0

Change it

1. Add a fourth println. Predict where it appears.
2. Comment out the second print by putting ;; at the beginning of its line.
3. Indent the program differently without changing delimiters. Predict whether the output changes. Restore readable indentation afterward.

Break and repair

In a copy, misspell println as printl. The smallest complete example of that mistake is deliberately rejected:

(defun main () -> i64
  (do (printl "one form") 0))

Save it as ex01-broken.fib, observe the diagnostic and repair the name. The book checks that this program is rejected; it is not a second working solution.

Checkpoint

Circle the delimiters that belong together. Explain why the semicolon inside the string prints, while the first line does not. Recreate a two-message program without looking at this page.

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