-
List: (x y z) -> S-expression
- Example:
(1 2 3 4 5) -> List of whole numbers until 5
-
Evaluation: (f x y z) -> First symbol is evaluated (considered to be a function)
- Example:
(+ 1 2 3 4 5) -> Addition on list of whole numbers until 5
-
Quotes: '(1 2 3 4 5) -> Do not evaluate first symbol, returns a list as is
- Example:
(println '(+ 1 2 3 4 5))
-
Global Symbols: Like variables/functions; References to S-expressions
- Example:
(define x 6) | (define l '(1 2 3 4 5))
-
Comments: Comments start with ; until EOL
- Example:
(define n 42) ; the meaning of life
-
Branching:
-
if:
- Syntax:
(if <cond> <true> [<false>] [... <cond> <true> [<false>]])
- Example:
(if should-reroute? (switch-to-other))
- Example:
(if (> 4 2) "4 > 2" "4 < 2") ; "4 > 2"
- Example:
(if (> 2 1) "2 > 1" (> 3 2) "3 > 2" "3 < 2") ; "2 > 1"
nil | () | unknown are false, rest true
-
when: Like an if without the else, can execute multiple exprs if true
(when (> 1 0)
(println "First body")
(println "Second body")
"I'm returned")
-
case: Switch to an expression based on value of case
(case v
(1 (print "ONE"))
(2 (print "TWO"))
(3 (print "THREE"))
(true (print v)))
- Case values are literals, not expressions; they are not evaluated
-
cond: check if conditions are true, then evaluate (mix of if and when)
; Syntax: (cond (<cond> <exprs>) [... (<cond> <exprs>)])
(cond
((> 1 x) (println "First") (println "Second"))
((> 10 x) (println "First Again") (println "Second Again"))
(true (println "Catch-all")))
-
Looping:
-
dolist: Loop on a list
; Syntax: (dolist <list> <exprs>)
(dolist (i (sequence 0 10))
(println "Element " i " at index " $idx))
-
dostring: Loop on a string
; Syntax: (dolist <string> <exprs>)
(dostring (code "abcdef") (println code))
-
dotimes: Loop for a count
; Syntax: (dotimes <counter> <exprs>)
(dotimes (c 10) (println c)) ; (c from 0 to <count>), here 0..9
-
for: Loop for a “custom” count
; Syntax: (for <custom counter> <exprs>)
(for (c 5 -5 .5) (println c)) ; (c <from> <to> <step>)
(for (c 1 10) (println c)) ; here 1..10
- break out early: Use a test condition to exit loop
```lisp
; Syntax: (looper (<counter> <test>) <exprs>) ; Stop if test is true
; Works in dolist, dostring and for as well
(dotimes (c 10 (= c 5)) (println c)) ; Stop at count 5
```
-
while (do-while): Loop for a condition success (opposite of until false)
; Syntax; (while <success-cond> <exprs>)
(while (disk-not-full?) (add-file))
-
until (do-until): Loop for a condition failure (opposite of while true)
; Syntax: (until <failure-cond> <exprs>)
(until (disk-full) (add-file)) ; Does the same as above while
-
map: Apply a function over a list
; Syntax: (map <fn> <list>)
(map println (sequence 0 10))
-
Lambas:
(fn (i) i * i) ; An anonymous function that returns square of i
-
Blocks: Groups of related but independent S-expressions; can be groups explicitly
-
begin: Group expressions into a single list, return value of last
(begin (first) (second) (third) (fourth) (return-fifth-value))
-
and: Finish all expressions and return truthy or fail one and return nil immediately
(and (first) (second) (third-fails-returns-null) (fourth-doesnt-run))
-
or: Finish expressions until a truthy value; return nil if none of them return true
(or (first-gives-nil) (second-gives-nil) (third-is-true) (fourth-not-evaled))
-
amb: chose a random (ambiguous) expressions to eval
(amb 1 2 3 4 5) ; returns a new number every time
-
Local Symbols: Variables valid only inside the S-expression they are defined in
; (let (<sym> <expr>) <exprs using sym>)
(let (x 2 y 3 z 4) (println x " " y " " z))
; letn (<sym1> <exprs> <sym2> <exprs using sym1>) <exprs using sym>)
; Used when symbols are used during initialization
-
Functions: Using “define”
; Syntax: (define (<name> <args>) <exprs>)
(define print-something (println "Something"))