I/O

Weir provides built-in functions for console output, file I/O, terminal control, and timing.

Console Output

println

Prints a value followed by a newline. Accepts zero or one argument:

(println "Hello, World!")      ;; prints: Hello, World!\n
(println 42)                   ;; prints: 42\n
(println)                      ;; prints a blank line

print

Prints a value without a trailing newline:

(print "Enter name: ")        ;; prints: Enter name: (no newline)
(print 42)                     ;; prints: 42

str

Not strictly I/O, but commonly used with it — concatenates values into a string:

(println (str "Score: " score " / " total))

File I/O

read-file

Reads the entire contents of a file as a string:

(defn load-config () : String
  (read-file "config.txt"))

(let ((data (read-file "level.dat")))
  (println (str "Loaded " (string-length data) " bytes")))

Parameter	Type	Description
path	String	File path to read
Returns	String	File contents

write-file

Writes a string to a file (creates or overwrites):

(write-file "output.txt" "Hello, file!")
(write-file "scores.txt" (str "High score: " high-score))

Parameter	Type	Description
path	String	File path to write
contents	String	String to write
Returns	Unit	—

Terminal I/O

For building terminal-based applications (e.g., the terminal Tetris demo):

term-init

Puts the terminal into raw mode — keypresses are delivered immediately without waiting for Enter:

(term-init)

term-restore

Restores the terminal to its normal (cooked) mode. Always call this before exiting to avoid leaving the terminal in a broken state:

(term-restore)

read-key

Reads a single keypress and returns the key code as an integer:

(let ((key (read-key)))
  (cond
    ((= key 27) (quit))           ;; ESC
    ((= key 119) (move-up))       ;; 'w'
    ((= key 115) (move-down))     ;; 's'
    (else (ignore))))

Requires term-init to have been called. Blocks until a key is pressed.

Timing

time-ms

Returns the current time in milliseconds (monotonic clock):

(let ((start (time-ms)))
  (do-expensive-work)
  (println (str "Took " (- (time-ms) start) "ms")))

sleep

Pauses execution for the given number of milliseconds:

(sleep 16)     ;; ~60 FPS frame delay
(sleep 1000)   ;; 1 second

Summary

Function	Signature	Description
println	(Fn ['a] Unit)	Print value + newline
print	(Fn ['a] Unit)	Print value (no newline)
read-file	(Fn [String] String)	Read entire file
write-file	(Fn [String String] Unit)	Write string to file
term-init	(Fn [] Unit)	Enter raw terminal mode
term-restore	(Fn [] Unit)	Restore normal terminal mode
read-key	(Fn [] i64)	Read single keypress
time-ms	(Fn [] i64)	Current time in milliseconds
sleep	(Fn [i64] Unit)	Sleep for N milliseconds