a sidebyside reference sheet
grammar and invocation  variables and expressions  arithmetic and logic  strings  dates and time  arrays  lists  tuples  dictionaries  functions  execution control  exceptions  concurrency  file handles  files  directories  processes and environment  libraries and namespaces  userdefined types  objects  inheritance and polymorphism  net and web  unit tests  debugging and profiling  repl
sml  ocaml  f#  haskell  

version used 
SML NJ 110  4.0  F# 3.0 Mono 3.2 
7.4 
show version 
displayed at startup  $ ocaml version  $ fsharpi help  $ ghc version 
grammar and invocation  
sml  ocaml  f#  haskell  
interpreter 
$ echo 'print_endline "hello"' > hello.ml $ ocaml hello.ml 
$ cat <<EOF > hello.fs module hello let main = printfn "hello" EOF $ fsharpi quiet exec hello.fs 
$ echo 'main = putStrLn "hello"' > hello.hs $ runghc hello.hs 

shebang  $ cat <<EOF > hello.ml #!/usr/bin/env ocaml print_endline "hello";; EOF $ chmod +x hello.ml $ ./hello.ml 
$ cat <<EOF > hello.fs #light (* exec fsharpi exec $0 quiet *) module hello printfn "hello" EOF $ chmod +x hello.fs $ ./hello.fs 
$ cat <<EOF > hello.hs #!/usr/bin/env runghc main = putStrLn "hello" EOF $ chmod +x hello.hs $ ./hello.hs 

bytecode compiler and interpreter  $ echo 'print_endline "hello";;' > hello.ml $ ocamlc o hello hello.ml $ ocamlrun hello 
$ echo 'printfn "hello"' > hello.fs $ fsharpc hello.fs $ mono hello.exe 
none  
native compiler  $ echo 'print_endline "hello";;' > hello.ml $ ocamlopt hello.ml o hello $ ./hello 
none  $ echo 'main = putStrLn "hello"' > hello.hs $ ghc o hello hello.hs $ ./hello 

library which is always imported  Pervasives  Core  Prelude  
statement terminator  ;  ;;  ;;  next line has equal or less indentation, or ; 
blocks  ( expr ; … )  ( expr ; … ) begin expr ; … end 
( expr ; … ) begin expr ; … end 
offside rule or { } 
endofline comment  none  none  // comment   comment 
multiple line comment  (* comment another comment *) 
(* comment another comment *) 
(* comment another comment *) 
{ comment another comment } 
variables and expressions  
sml  ocaml  f#  haskell  
writeonce variable 
val a = 3;  let n = 1 + 2;;  let n = 1 + 2  n = 3 
modifiable variable  val a = ref 3; a := 4; !a + 7; 
let n = ref 3;; n := 4;; !n + 7;; 
let n = ref 3 n := 4 !n + 7 
n < return 3 
unit type and value  unit () 
unit () 
unit () 
() () 
conditional expression  val x = 3; if x < 0 then ~x else x; 
let n = 3;; let absn = if n < 0 then n else n;; 
let n = 3 let absn = if n < 0 then n else n 
n = 3 let absn = if n < 0 then n else n 
branch type mismatch  (* compilation error: *) if true then "hello" else 3; 
(* compilation error: *) if true then "hello" else 3;; 
(* compilation error: *) if true then "hello" else 3 
 compilation error: if True then "hello" else 3 
null 
NONE  None  None Also this value returned by .NET library functions. It has a type distinct from None: null 
Nothing 
nullable type  type list_option_int = int option list; val list = [SOME 3,NONE, SOME ~4]; 
type list_option_int = int option list;; let list = [Some 3; None; Some (4)];; 
list = [Just(3), Nothing, Just(4)]  
null test  match foo with  None > true  _ > false;; 

coalesce  val foo = SOME 3; (* raises exception if NONE: *) valOf foo; (* evaluates to 0 if NONE: *) getOpt (foo, 0); 
match foo with  None > 0  Some n > n;; 
import Data.Maybe let foo = Just(3) raises exception if Nothing: fromJust foo let intId x = x evaluates to 0 if Nothing: maybe 0 intId foo 

nullif  match foo with  999 > None  n > Some n;; 

expression type declaration  float 1  float 1  1 :: Double  
let ... in ...  val z = let val x = 3.0 val y = 2.0 * x in x * y end; 
let z = let x = 3.0 in let y = 2.0 *. x in x *. y;; 
let z = let x = 3.0 in let y = 2.0 * x in x * y 
z = let x = 3.0 y = 2.0 * x in x * y 
where  none  none  none  z = x * y where x = 3.0 y = 2.0 * x 
arithmetic and logic  
sml  ocaml  f#  haskell  
boolean type 
bool  bool  bool  Bool 
true and false 
true false  true false  true false  True False 
logical operators  andalso orelse not  &&  not  &&  not  &&  not 
relational operators  = <> < > <= >=  = <> < > <= >=  = <> < > <= >=  == /= < > <= >= 
min and max  min 1 2 max 1 2 
min 1 2 max 1 2 
min 1 2 max 1 2 

integer type  int  int other integer types: int32 int64 nativeint 
int other integer types: int32 int64 nativeint 
Integer 
integer literal  negative integer: ~4 
int, int64, and nativeint literals: 12 12L 12n literals can contain underscores: 1_000_000 this parses as an expression: 4 
4  an expression, not a literal: 4 
float type  real  float  float  Double 
integer operators  +  * div mod  +  * / mod mod //is an infix operator 
+  * / %  +  * div rem div and rem are functions, not infix operators 
float operators 
+  * /  +. . *. /.  +  * /  +  * / 
add integer and float  real 3 + 7.0;  float 3 +. 7.0  float 3 + 7.0  3 + 7.0 
integer division and remainder 
7 div 3 7 mod 3 real 7 / real 3 
7 / 3 7 mod 3 
7 / 3 7 % 3 
div 7 3 rem 7 3 
integer division by zero  raises Division_by_zero  System.DivideByZeroException  Exception: divide by zero  
float division 
float 7 /. float 3  float 7 / float 3  7 / 3  
float division by zero  infinity nan or neg_infinity  infinity nan or neg_infinity  evaluates to Infinity, NaN, or Infinity, values which do not have literals  
power  Math.pow (2.0, 32.0);  2.0 ** 32.0  2.0 ** 32.0  2 ** 32  syntax error if exponent not an integer: 2 ^ 32 
sqrt 
Math.sqrt 2.0  sqrt 2.0  sqrt 2.0  sqrt 2 
sqrt 1  Math.sqrt ~1.0 evaluates to nan  sqrt (1.0): nan 
nan  sqrt (1) evaluates to NaN, a value which has no literal 
transcendental functions  Math.exp Math.ln Math.sin Math.cos Math.tan Math.asin Math.acos Math.atan Math.atan2 
exp log sin cos tan asin acos atan atan2 
exp log sin cos tan asin acos atan atan2 
exp log sin cos tan asin acos atan atan2 
transcendental constants  Math.pi Math.e 
4.0 *. atan 1.0 exp 1.0 
System.Math.PI System.Math.E 
pi exp 1 
float truncation  round 3.14 trunc 3.14 floor 3.14 ceil 3.14 
truncate 3.14 none floor 3.14 returns float ceil 3.14 returns float 
truncate 3.14 round 3.14 floor 3.14 returns float ceil 3.14 returns float 
truncate 3.14 round 3.14 floor 3.14 ceiling 3.14 
absolute value and signum 
abs (7) abs_float (7.0) no signum 
abs 7 abs 7.0 sign 7 sign 7.0 
abs (7) signum (7) 

integer overflow  Overflow exception  modular arithmetic  modular arithmetic  has arbitrary length integers 
float overflow  infinity  infinity  evaluates to Infinity, a value which has no literal  
arbitrary length integer  open Big_int;; let n = big_int_of_int 7;; let m = big_int_of_int 12;; 
// System.Numerics.BigInteger: let n = 7I let m = 12I 
 Integer is arbitrary length type: let n = 7 let m = 12 

arbitrary length integer operators  add_big_int n m sub_big_int n m mult_big_int n m div_big_int n m (* quotient *) mod_big_int n m eq_big_int n m lt_big_int n m gt_big_int n m le_big_int n m ge_big_int n m 
n + m n  m n * m n / m n % m n = m n < m n < m n <= m n >= m 
n + m n  m n * m div n m mod n m n == m n < m n < m n <= m n >= m 

rational type  Ratio Integer  
rational construction  import Data.Ratio 1 % 7 

rational decomposition  import Data.Ratio numerator (1 % 7) denominator (1 % 7) 

complex type  Complex.t  Complex Double  
complex constants  Complex.zero Complex.one Complex.i 

complex operators  Complex.add z w;; Complex.sub z w;; Complex.mul z w;; Complex.div z w;; 

complex construction  {Complex.re=1.0; Complex.im=2.0}  System.Numerics.Complex(1.0, 2.0)  import Data.Complex 1 :+ 2.0 

complex decomposition  let z = {Complex.re=1.0; Complex.im=2.0};; z.Complex.re;; z.Complex.im;; Complex.arg z;; Complex.norm z;; Complex.conj z;; 
import Data.Complex realPart (1 :+ 2) imagPart (1 :+ 2) phase (1 :+ 2) magnitude (1 :+ 2) conjugate (1 :+ 2) 

random number uniform int, uniform float, normal float 
Random.int 100 Random.float 1.0 none 
let rnd = System.Random() rnd.Next(0, 100) rnd.NextDouble() none 
 $ cabal install random import System.Random getStdRandom (randomR (0, 99)) getStdRandom (randomR (0.0, 1.0)) none 

random seed set, get, restore 
Random.init 17;; let seed = Random.get_state();; Random.set_state seed;; 
let rnd = System.Random(17) none none 
 $ cabal install random import System.Random setStdGen $ mkStdGen 17 seed < getStdGen setStdGen seed 

bit operators  1 lsl 4 1 lsr 4 1 land 3 1 lor 3 1 lxor 3 lnot 1 
1 <<< 4 1 >>> 4 1 &&& 3 1  3 1 ^^^ 3 ~~~ 1 
import Data.Bits x = 1 :: Integer y = 3 :: Integer shiftL x 4 shiftR x 4 x .&. y x .. y xor x y complement x 

binary, octal, and hex literals  0b101010 0o52 0x2a 
0b101010 0o52 0x2a 
none 052 0x2a 

radix  
strings  
sml  ocaml  f#  haskell  
string type 
string  string  string  String 
string literal 
"Hello, World!"  "Hello, World!"  "Hello, World!"  "Hello, World!" 
newline in literal  no  yes  no  
literal escapes  \000 \a \b \f \n \r \t \v \040  \b \n \r \t \" \' \\ \ooo \xhh 
\b \n \r\ t \" \' \\ \uhhhh \Uhhhhhhhh 
\a \b \f \n \r \t \v \" \& \' \\ \oo... \d... \xh... Octal, decimal, and hex escapes denote Unicode characters and can contain anywhere from 1 to 7 digits. The max values are \o4177777, \1114111, and \x10ffff. The \& escape does not represent a character, but can separate a numeric backslash escape sequence from a following digit. 
format string  sprintf "foo %s %d %.2f" "bar" 7 3.1415  import Text.Printf printf "foo %s %d %.2f" "bar" 7 3.1415 

concatenate 
"Hello" ^ ", " ^ "World!"  "Hello" ^ ", " ^ "World!"  "Hello" + ", " + "World!"  "Hello" ++ ", " ++ "World!" 
replicate 
String.make 80 ''  String.replicate 80 ""  concat ( replicate 80 "" )  
translate case to upper, to lower 
String.uppercase "hello" String.lowercase "HELLO" 
"hello".ToUpper() "HELLO".ToLower() 
import Data.Char map toUpper "hello" map toLower "HELLO" 

capitalize 
String.capitalize "hello"  
trim both sides, left, right 
String.trim " hello "  " hello ".Trim() " hello".TrimStart() "hello ".TrimEnd() 

pad on left, on right 
"hello".PadLeft(10, ' ') "hello".PadRight(10, ' ') 

number to string  "two: " ^ string_of_int 2 "pi: " ^ float_of_string 3.14 
"two: " + string 2 "pi: " + string 3.14 
"two: " ++ (show 2) "pi: " ++ (show 3.14) 

string to number  Int.toString 3 Real.toString 3.14 
7 + int_of_string "12" 73.9 +. float_of_string ".037" 
7 + int "12" 73.9 + float ".037 
7 + (read "12")::Integer 73.9 + (read "0.037")::Double raises exception if string doesn't completely parse 
join 
System.String.Join(" ", ["do"; "re"; "mi"])  
split 
"do re mi".Split(' ')  
character type 
char  char  char  Char 
character literal  #"h"  'h'  'h'  'h' 
length 
size "hello"  String.length "hello"  "hello".Length  length "hello" 
index of substring  "hello".IndexOf("hell")  
extract substring  substring ("hello",0,4)  String.sub "hello" 0 4  "hello".Substring(0, 4)  drop 0 (take 4 "hello") 
extract character  String.sub ("hello", 0)  "hello".[0]  "hello".[0]  "hello" !! 0 
chr and ord  ord #"a" chr 97 
Char.code 'a' Char.chr 97 
int 'a' char 97 
Char.ord 'a' Char.chr 97 
dates and time  
sml  ocaml  f#  haskell  
date and time types  ClockTime CalendarTime TimeDiff  
current date and time  import Time t < getClockTime 

current unix epoch  open Unix;; (* float: *) time();; 
import System.Time getClockTime >>= (\(TOD sec _) > return sec) 

arrays  
sml  ocaml  f#  haskell  
literal  
size  
lookup  
update  
outofbounds  
lists  
sml  ocaml  f#  haskell  
literal  [1, 2, 3]  [1; 2; 3]  [1; 2; 3]  [1, 2, 3] 
empty list 
[]  []  
empty list test  let list = [1; 2; 3];; list == [] 
let list = [1, 2, 3] list == [] null list 

cons 
1 :: [2, 3]  1 :: [2; 3]  1 :: [2; 3]  1 : [2, 3] 
head 
List.hd [1, 2, 3]  List.hd [1; 2; 3]  List.head [1; 2; 3]  head [1, 2, 3] 
tail 
List.tl [1, 2, 3]  List.tl [1; 2; 3]  List.tail [1; 2; 3]  tail [1, 2, 3] 
head and tail of empty list  exceptions  exceptions  
length 
List.length [1, 2, 3]  List.length [1; 2; 3]  List.length [1; 2; 3]  length [1, 2, 3] 
nth element 
List.nth ([1, 2, 3], 0)  List.nth [1; 2; 3] 0  List.nth [1; 2; 3] 0  [1, 2, 3] !! 0 
element index  import Data.list  Just 1: elemIndex 8 [7, 8, 9]  Nothing: elemIndex 10 [7, 8, 9] 

update  
concatenate two lists, list of lists 
[1, 2] @ [3, 4] List.concat [[1, 2], [3, 4]] 
[1; 2] @ [3; 4] List.append [1; 2] [3; 4] List.concat [[1; 2]; [3; 4]] 
[1; 2] @ [3; 4] List.append [1; 2] [3; 4] List.concat [[1; 2]; [3; 4]] 
[1, 2] ++ [3, 4] concat [[1, 2], [3, 4]] 
last and butlast 
last [1, 2, 3] init [1, 2, 3] 

take 
take 2 [1, 2, 3]  
drop 
drop 2 [1, 2, 3]  
iterate  fun f i = print ((Int.toString i) ^ "\n"); List.app f [1, 2, 3]; 
let f i = print_endline (string_of_int i);; List.iter f [1; 2; 3];; 
let f i = System.Console.WriteLine(string i) List.iter f [1; 2; 3] 
mapM_ print [1, 2, 3] 
reverse 
List.rev [1, 2, 3]  List.rev [1; 2; 3]  List.rev [1; 2; 3]  reverse [1, 2, 3] 
sort  List.sort min [1; 3; 2; 4] List.sort max [1; 3; 2; 4] 
List.sort [1; 3; 2; 4]  import Data.List sort [1, 3, 2, 4] 

map  List.map (fn (x) => x + 2) [1, 2, 3];  List.map (( * ) 2) [1; 2; 3]  List.map (( * ) 2) [1; 2; 3]  map (\x > x * x) [1, 2, 3] 
filter 
List.filter (fn (x) => x > 2) [1, 2, 3];  List.filter ((<) 2) [1; 2; 3]  List.filter ((<) 2) [1; 2; 3]  filter (\x > x > 2) [1, 2, 3] 
fold from left  List.foldl (op +) 0 [1, 2, 3];  List.fold_left (+) 0 [1; 2; 3]  List.fold () 0 [1; 2; 3]  foldl (+) 0 [1, 2, 3] 
fold from right 
List.fold_right () [1; 2; 3] 0  List.foldr (op ) 0 [1, 2, 3];  foldr () 0 [1, 2, 3]  
membership 
List.mem 3 [1; 2; 3]  elem 3 [1, 2, 3]  
universal test 
List.for_all (fun x > x > 2) [1; 2; 3];;  List.forall (fun x > x > 2) [1; 2; 3]  all (\x > x > 2) [1, 2, 3]  
existential test 
List.exists (fun x > x > 2) [1; 2; 3];;  List.exists (fun x > x > 2) [1; 2; 3]  any (\x > x > 2) [1, 2, 3]  
zip lists  (* list of tuples *) List.combine [1; 2; 3] ['a'; 'b'; 'c'] 
 list of tuples: zip [1, 2, 3] ['a', 'b', 'c'] 

tuples  
sml  ocaml  f#  haskell  
literal  (1, "hello", true)  (1, "hello", true)  (1, "hello", true)  (1, "hello", True) 
lookup  #1 (1, "hello", true)  match (1, "hello", true) with _, x, _ > x  match (1, "hello", true) with _, x, _ > x  (\(a, _, _) > a) (1, "hello", True) 
pair lookup  #1 (12,"December") #2 (12,"December") 
fst (12, "December") snd (12, "December") 
fst (12, "December") snd (12, "December") 
fst (12, "December") snd (12, "December") 
dictionaries  
sml  ocaml  f#  haskell  
functions  
sml  ocaml  f#  haskell  
define function  fun average a b = ( a + b ) / 2.0;  let average a b = ( a +. b ) /. 2.0;;  let average a b = ( a + b ) / 2.0  average a b = (a + b) / 2.0 
invoke function  (* 4.5: *) average 1.0 2.0 +. 3.0;; (* 3.0: *) average 1.0 (2.0 +. 3.0);; 
// 4.5: average 1.0 2.0 + 3.0 // 3.0: average 1.0 (2.0 + 3.0) 
 4.5: average 1 2 + 3  3.0: average 1 (2 + 3) average 1 $ 2 + 3 

named parameter  let subtract ~m ~s = m  s;; subtract ~s: 3 ~m: 7;; 
none  
named parameter default value  let logarithm ?(base = (exp 1.0)) x = log x /. (log base);; logarithm 2.718;; logarithm ~base: 2.0 10.0;; 
none  
piecewise defined function  val to_s = fn Red => "red"  Green => "green"  Blue => "blue"; 
let to_s = function Red > "red"  Green > "green"  Blue > "blue";; 
to_s Red = "red" to_s Green = "green" to_s Blue = "blue" 

recursive function  fun range a b = if a > b then [] else a :: range (a + 1) b; 
let rec range a b = if a > b then [] else a :: range (a+1) b;; 
range a b = if a > b then [] else a : range (a+1) b  
mutuallyrecursivefunctions  let rec even n = if n = 0 then true else odd (n1) and odd n = if n = 0 then false else even (n1);; 

anonymous function  fn x => fn y => (x + y) / 2.0  fun x > fun y > (x +. y) /. 2.0  fun x > fun y > (x + y) / 2.0  \x y > (x+y) / 2.0 
infix operator in prefix position  (op * ) (3, 4)  ( * ) 3 4;;  ( * ) 3 4  
function in infix position  none  add x y = x + y 3 ‘add` 4 

currying  un plus x y = x + y; val plus2 = plus 2; plus2 7; 
let plus2 = (+) 2;;  plus2 = (+) 2  
composition  f x = x + 2 g x = x * 3 (f . g ) 4 

function composition operator  fun double x = 2 * x; val quadruple = double o double; 
none  double x = 2 * x quadruple x = double . double 

lazy evaluation  let arg1 x y = x;; arg1 7 (lazy (1/0) );; 
lazy evaluation is default: arg1 x y = x arg1 7 (error "bam!") 

strict evaluation  default behavior  default behavior  arg1 x y = seq y x arg1 7 (error "bam!") 

execution control  
sml  ocaml  f#  haskell  
if  f x > 0 then print "pos\n" else (); 
if x > 0 then print_endline "pos";; 
if x > 0 then printfn "pos" 
if x > 0 then putStrLn "pos" else return () 
if elseif else  if x > 0 then print "pos" else if x < 0 then print "neg" else print "zero";  if x > 0 then print_endline "pos" else if x < 0 then print_endline "neg" else print_endline "zero";; 
if x > 0 then printfn "pos" else if x < 0 then printfn "neg" else printfn "zero" 
if x > 0 then putStrLn "pos" else if x < 0 then putStrLn "neg" else putStrLn "zero" 
sequencing  print_endline "one"; print_endline "two"; print_endline "three";; 
printfn "one" printfn "two" printfn "three" 
do putStrLn "one" putStrLn "two" putStrLn "three" 

while  let i = ref 0;; while !i < 10 do print_endline (string_of_int !i); i := !i + 1 done;; 
let i = ref 0 while !i < 10 do printfn "%d" !i i := !i + 1 

for  for i = 1 to 10 do let s = string_of_int i in print_endline s done;; 

for in reverse  for i = 10 downto 1 do let s = string_of_int i in print_endline s done;; 

list iteration  none  
loop  let rec loop i = if i <= 10 then begin print_endline (string_of_int i); loop (i+1) end in loop 0;; 

exceptions  
sml  ocaml  f#  haskell  
raise error  raise (Failure "bam!");; or failwith "bam!";; 
error "bam!"  
handle error  let x = try 1 / 0 with Division_by_zero > 0;;  
type of exceptions  exn  
user defined exception  exception Foo of string;; raise (Foo "invalid input");; 

standard exceptions  Division_by_zero Failure string Not_found Invalid_argument string Match_failure (string, int, int) Assert_failure (string, int, int) Out_of_memory Stack_overflow 

assert  assert(1 = 0);;  
concurrency  
sml  ocaml  f#  haskell  
file handles  
sml  ocaml  f#  haskell  
standard file handles  stdin stdout stderr  stdin stdout stderr  import System.Posix.IO stdInput stdOutput stdError 

read line from stdin  let line = read_line();;  line < getLine  
endoffile behavior  raises End_of_file  when last data is returned, hIsEOF will return True. Reading after endoffile throws an exception.  
chomp  
write line to stdout  print_endline "lorem ipsum";;  printfn "lorem ipsum"  putStrLn "lorem ipsum"  
write formatted string to stdout  
open file for reading  let f = open_in "/etc/passwd";;  import System.IO f < openFile "/etc/hosts" ReadMode 

open file for writing  let f = open_out "/tmp/ocaml.out";;  import System.IO f < openFile "/tmp/test" WriteMode 

open file for appending  import System.IO f < openFile "/tmp/err.log" AppendMode 

close file  import System.IO hClose f 

i/o errors  
read line  fun displayFile(file: string) = let val f = TextIO.openIn file fun iter(s: string option) = case s of NONE => (TextIO.closeIn f)  SOME(line) => (print line; iter(TextIO.inputLine f)) in iter(TextIO.inputLine f) end displayFile("/etc/passwd"); 
let ic = open_in "/etc/passwd" in let line = input_line ic in print_endline line;; 
import IO readAndPrintLines h = do eof < hIsEOF h if eof then return () else do line < hGetLine h putStrLn line readAndPrintLines h main = do h < openFile "/etc/passwd" ReadMode readAndPrintLines h 

iterate over file by line  
read file into array of strings  
read file into string  
write string  
write line  val file = "/tmp/testsml"; val f = TextIO.openOut file; TextIO.output(f, "hello out\n"); TextIO.closeOut f; 
open Printf let oc = open_out "/tmp/testocaml" in fprintf oc "hello out\n"; close_out oc;; 
s = "hello out\n" f = "/tmp/testhaskell" main = writeFile f s 

flush file handle  
endoffile test  
get and set filehandle position  
files  
sml  ocaml  f#  haskell  
file test, regular file test  open Unix try Some (stat "/etc/hosts") with Unix_error (ENOENT, _, _) > None (stat "/etc/hosts").st_kind = S_REG 
import System Directory.doesFileExist "/etc/hosts" import Control.Monad import System.Posix.Files liftM isRegularFile (getFileStatus "/etc/hosts") 

file size  (stat "/etc/hosts").st_size  import Control.Monad import System.Posix.Files liftM fileSize (getFileStatus "/etc/hosts") 

is file readable, writable, executable  open Unix try access "/tmp/bar" [R_OK]; true with Unix.Unix_error (EACCES, _, _) > false;; try access "/tmp/bar" [W_OK]; true with Unix.Unix_error (EACCES, _, _) > false;; try access "/tmp/bar" [X_OK]; true with Unix.Unix_error (EACCES, _, _) > false;; 
import Control.Monad liftM readable (getPermissions "/etc/hosts") liftM writable (getPermissions "/etc/hosts") liftM executable (getPermissions "/etc/hosts") 

set file permissions  open Unix chmod "/tmp/foo" 0o755 
import System.Posix.Files setFileMode "/tmp/foo" ownerModes setFileMode "/tmp/foo" groupReadMode setFileMode "/tmp/foo" groupExecuteMode setFileMode "/tmp/foo" otherReadMode setFileMode "/tmp/foo" otherExecuteMode 

copy file, remove file, rename file  open Unix ?? unlink "/tmp/foo" rename "/tmp/bar" "/tmp/foo" 
import System.Directory copyFile "/tmp/foo" "/tmp/bar" removeFile "/tmp/foo" renameFile "/tmp/bar" "/tmp/foo" 

create symlink, symlink test, readlink  open Unix symlink "/etc/hosts" "/tmp/hosts" (lstat "/tmp/hosts").st_kind = S_LNK readlink "/tmp/hosts" 
import System.Posix.Files createSymbolicLink "/etc/hosts" "/tmp/hosts" ?? readSymbolicLink "/tmp/hosts" 

generate unused file name  open Filename (* prefix and suffix: *) temp_file "foo" ".txt" 

directories  
sml  ocaml  f#  haskell  
build pathname  open Filename concat "/etc" "hosts" 
import System.FilePath ((</>)) let path = "/etc" </> "hosts" 

dirname and basename  open Filename dirname "/etc/hosts" basename "/etc/hosts" 
import System.FilePath takeFileName "/etc/hosts" takeDirectory "/etc/hosts" 

iterate over directory by file  import System  returns IO [FilePath] Directory.getDirectoryContents "/etc" 

make directory  (* opam install fileutils *) open FileUtil mkdir ~parent:true "/tmp/foo/bar" 
import System.Directory createDirectoryIfMissing True "/tmp/foo/bar" 

remove empty directory  open Unix rmdir "/tmp/foodir" 
import System.Directory removeDirectory "/tmp/foodir" 

remove directory and contents  import System.Directory removeDirectoryRecursive "/tmp/foodir" 

directory test  import System Directory.doesDirectoryExist "/tmp" 

temporary directory  
processes and environment  
sml  ocaml  f#  haskell  
command line arguments  for i = 0 to Array.length Sys.argv  1 do print_endline i Sys.argv.(i) done 
import System printArgs args = do if length args == 0 then return () else do putStrLn (head args) printArgs (tail args) main = do a < getArgs printArgs a 

program name 
import System s < getProgName 

getopt  
get and set environment variable 
open Unix s = getenv "HOME" putenv "PATH" "/bin" 
import System.Posix.Env s < getEnv "HOME" putEnv "PATH=/bin" 

get pid, parent pid  open Unix let pid = getpid() let ppid = getppid() 
import System.Posix.Process pid < getProcessID ppid < getParentProcessID 

get user id and name  let uid = getuid() let username = (getpwuid (getuid())).pw_name 
import System.Posix.User uid < getRealUserID username < getLoginName 

exit 
exit 0 exit 1 
import System.Exit exitWith ExitSuccess to return nonzero status: exitWith (ExitFailure 1) 

set signal handler 

external command 
import System.Cmd rawSystem "ls" ["l", "/tmp"] 

escaped external command 

backticks 

libraries and namespaces  
sml  ocaml  f#  haskell  
namespace example  Foo/Bar.hs module Foo.Bar where data Baz = Baz say Baz = putStrLn "hello" Main.hs module Main where import Foo.Bar baz = Baz main = say baz to compile and run $ ghc c Foo/Bar.hs $ ghc Main.hs $ ./Main hello 

namespaces  values, constructors, type variables, type constructors, type classes, modules  
file name restrictions  module Foo.Bar must be in Foo.ml  module Foo.Bar must be in Foo/Bar.hs  
namespace  open Graphics;;  import Data.Bytestring  
namespace creation  put code in file MODULE_NAME.ml  
namespace alias  module Gr = Graphics;;  import qualified Data.Bytestring as B  
namespace separator  .  .  
subnamespace  in A.ml: module B = sig val display_instruction : unit > unit end = struct let msg = "attack" let display_instruction () = print_endline msg end in client source: A.B.display_instruction;; 

package manager setup  do this once: $ opam init for each shell session: $ eval $(opam config env) 

package manager search; install; list installed 
$ opam search utop $ opam install utop $ opam list installed 
$ cabal list parsec $ cabal install parsec $ cabal list installed 

compile app using package  
userdefined types  
sml  ocaml  f#  haskell  
type synonym 
type name = string;  type name = string;;  type name = string  type Name = String 
sum type  datatype color = Red  Green  Blue;  type color = Red  Green  Blue;; let col = Red;; (* evaluates to true: *) col < Green;; 
type color = Red  Green  Blue let col = Red // evaluates to true: col < Green 
data Color = Red  Green  Blue col = Red  this won’t compile: col < Green 
tuple product type with one field  datatype special_int = SpecialInt of int; val x = SpecialInt 7; 
type special_int = SpecialInt of int;; let n = SpecialInt 7;; 
type special_int = SpecialInt of int let n = SpecialInt 7 
data SpecialIntType = SpecialInt Integer n = SpecialInt 7 
tuple product type with two fields  datatype int_pair = IntPair of int * int; val y = IntPair (7, 11); 
type int_pair = IntPair of int * int;; let p = IntPair (7, 11);; 
type int_pair = IntPair of int * int let p = IntPair (7, 11) 
data IntPairType = IntPair Integer Integer p = IntPair 7 11 
record product type  type customer = {id:int, name:string, address:string}  type customer = { id: int; name: string; address: string };; 
type customer = { id: int; name: string; address: string } 
data CustomerType = Customer { customerId :: Integer, name :: String, address :: String } 
record product type literal  {id=7, name="John", address="Topeka, KS"}  let cust = { id=7; name="John"; address="Topeka, KS" };; 
{id=7; name="John"; address="Topeka, KS"}  Customer { customerId=7, name="John", address="Topeka, KS" } 
generic type  datatype ('a, 'b) twosome = Twosome of 'a * 'b; val z = Twosome ("pi", 3.14); 
type ('a, 'b) twosome = Twosome of 'a * 'b;; let p = Twosome ("pi", 3.14);; 
type ('a, 'b) twosome = Twosome of 'a * 'b let p = Twosome ("pi", 3.14) 
data TwosomeType a b = Twosome a b p = Twosome ("pi", 3.14) 
recursive type  datatype binary_tree = Leaf of int  Tree of binary_tree * binary_tree; 
type binary_tree =  Leaf of int  Tree of binary_tree * binary_tree;; 
type binary_tree =  Leaf of int  Tree of binary_tree * binary_tree 
data BinaryTree = Leaf Integer  Tree BinaryTree BinaryTree 
pattern match sum type  val c = Red; case c of Red => "red"  Blue => "blue"  Green => "green"; 
let col = Red;; let s = match col with  Red > "red"  Blue > "blue"  Green > "green";; 
c = Red case c of Red > "red" Green > "green" Blue > "blue" 

pattern match product type  
pattern match guard  none; use if  match i with j when i < 0 > j  j > j;;  none, use if or piecewise function definition  
pattern match catchall  fun to_s c = case c of Red => "red"  _ => "not red";  let to_s c = match c with Red > "red"  _ > "not red";; to_s Green;; 
c = Green case c of Red > "red"; _ > "not red" 

objects  
sml  ocaml  f#  haskell  
class definition  class counter = object val mutable n = 0 method incr = n < n+1 method get = n end;; 

object creation  let c = new counter;;  
method invocation  c#incr;; c#get;; 

field access  none  
inheritance and polymorphism  
sml  ocaml  f#  haskell  
overload function  
inheritance  
net and web  
sml  ocaml  f#  haskell  
unit test  
sml  ocaml  f#  haskell  
debugging and profiling  
sml  ocaml  f#  haskell  
repl  
sml  ocaml  f#  haskell  
invoke repl  $ sml  $ ocaml Use this if you want history: $ rlwrap ocaml The utop toplevel, which can be installed via opam, also provides history. 
Mono: $ fsharpi In visual studio, highlight code and press ALT+ENTER. 
$ ghci 
repl limitations  Must use let to define values and functions; when defining functions with multiple equations the equations must be separated by semicolons; the clauses of case/of statements must be separated by semicolons; it is not possible to define data types.  
repl last value  it  none  it  it 
help  none  :?  
quit  ^D  #quit;;  
inspect type  repl displays the type of any expression entered  let a = 3 :type a 

inspect namespace  module Unix = Unix;;  
load source file  use "hello.ml";  #use "hello";;  :edit hello.hs :load hello 

load package  consider adding to .ocamlinit: #use "topfind";; # thread;; #require "core";; open Core.Std;; 

search path  #directory "libdir";;  
set search path on command line  ocaml Ilibdir  
_______________________________________________  _______________________________________________  _______________________________________________  _______________________________________________ 
version used
Versions used to test the code samples in this sheet.
show version
How to get the version.
Grammar and Invocation
interpreter
How to run the interpreter on a file of source code.
shebang
How to use the interpreter in a shebang.
bytecode compiler and interpreter
How to compile source to bytecode and run it.
ocaml:
It is not necessary to invoke ocamlrun on the bytecode; the bytecode can be executed directly because the bytecode compiler puts a shebang invocation at the top of the file.
native compiler
How to compile source to native code and run it.
library which is always imported
The name of the library containing the types and functions which are always available.
statement terminator
ocaml:
;; is the ocaml statement separator. It is not necessary at the end of the line if the following line starts with an open or let keyword or at the end of the file.
blocks
How to define a block of statements.
endofline comment
A comment terminated by the end of the line.
multiple line comment
A comment with a start and end delimiter which can span multiple lines.
ocaml:
(* *) style comments can be nested.
Variables and Expressions
writeonce variable
How to define a variable which can be set at runtime but cannot be modified after it is set.
modifiable variable
How to define a modifiable variable.
unit type and value
The notation for the unit type and the unit value. In all languages the notation for the unit value is the same as the notation for an empty tuple.
The unit value is a common return value of functions which perform side effects.
conditional expression
The syntax for a conditional expression.
branch type mismatch
What happens if the two branches of a conditional expression don't have the same type.
null
A value used somewhat paradoxically to indicate the absence of a value.
Types which can contain a null value are called option types.
nullable type
null test
coalesce
expression type declaration
How to explicitly declare the type of an expression.
let ... in ...
How to define local variables.
ocaml:
OCaml uses let to define a value and let with in to define values in a local scope. OCaml follows the usage of the original dialect of ML in this respect.
OCaml can define multiple values with a single let and in by conjoining the definitions with and. The definitions are performed in parallel, so later definitions cannot use the earlier definitions:
let z =
let x = 3
and y = 4 in
x * y;;
haskell:
Haskell uses let with in to define local scope. In addition, ghci uses let without in to define values.
where
How to define local variables with definitions after the expression that uses them.
Arithmetic and Logic
boolean type
The type for boolean values.
true and false
The literals for true and false.
logical operators
The logical operators: and, or, and not.
relational operators
Operators for performing comparisons.
min and max
The binary functions min and max.
integer types
The most commonly used numeric types.
integer literal
Integer literals.
haskell:
Haskell does not have negative integer literal syntax. The negative sign parses as a unary prefix operator. It may be necessary to put parens around a negative integer constant:
 syntax error:
1 + 3
 ok:
1 + (3)
float type
Floating point types.
integer operators
The integer operators.
float operators
The floating point operators. Note that in the OCaml the floating point operators are different from the integer operators.
add integer and float
How to add an integer and a float.
ocaml:
OCaml also can convert a integer to float with float_of_int.
integer division
How to find the quotient of two integers; how to find the remainder of two integers.
integer division by zero
The result of dividing an integer by zero.
float division
float division by zero
The result of division by zero.
float exponentiation
How to exponentiate a float.
float functions
The square root function; the natural exponential and natural logarithm functions; the trigonometric functions.
arithmetic truncation
Ways to convert a float to a nearby integer.
ocaml:
This definition of round handles negative numbers correctly:
let round x = int_of_float (floor (x +. 0.5))
power
How to perform exponentiation.
ocaml:
How to define a function which computes the power of an integer:
let integer_exponent b e =
let rec aux x i =
if i = e then x else aux (x * b) (i + 1)
in
aux 1 0;;
sqrt 1
The result of taking the square root of a negative number.
transcendental functions
transcendental constants
integer overflow
What happens when expression evaluates to an integer that is larger than what can be stored.
float overflow
The result of float overflow.
Ocaml has literals for infinity and negative infinity, but Scala and Haskell do not.
rational type
rational construction
rational decomposition
complex type
complex construction
complex decomposition
random number
How to generate a uniformly distributed random integer; how to generate a uniformly distributed float; how to generate a normally distributed float.
random seed
How to set a random seed. How to get and restore the state of a random number generator.
bit operators
The bit operators.
ocaml:
Also has operators which perform arithmetic shift: asl and asr. When performing an arithmetic shift, the sign of the integer is preserved.
haskell:
Haskell does not assign a default size or type to numeric literals. Hence numeric literals must have their type declared for bit operations to be performed on them.
binary, octal, and hex literals
radix
Strings
string type
The types for strings and characters.
string literal
The syntax for a string literal.
newline in literal
literal escapes
format string
concatenate
How to concatenate strings.
f#:
F# supports (with a warning) the ^ operator for compatibility with OCaml.
replicate
translate case
How to convert a string to uppercase; how to convert a string to lowercase; how to capitalize the first character.
capitalize
trim
pad
number to string
string to number
How to parse numeric types from string; how to convert numeric types to strings.
ocaml:
To convert a string to a float:
float_of_string "3.14"
join
split
character type
character literal
length
How to get the length of a string.
index of substring
How to get the index of a substring.
extract substring
How to extract a substring.
extract character
How to get the character at a specified index of a string.
The syntax for a character literal.
chr and ord
How to convert a character to its ASCII code or Unicode point; how to convert an ASCII code or Unicode point to a character.
Dates and Time
Arrays
Lists
list literal
list element element
list head
f#:
Supports List.hd (with a warning) to be compatible with OCaml.
listtail
Supports List.tl (with a warning) to be compatible with OCaml.
Tuples
tuple
tuple element
Functions
function
How to define a function.
lambda
How to define an anonymous function.
piecewise defined function
How to define a function with multiple equations and matching on the arguments.
recursive function
How to define a recursive function.
mutually recursive functions
How to define two functions which call each other. Mutual recursion can be eliminated by inlining the second function inside the first function. The first function is then recursive and can be defined independently of the second function.
named parameter
How to define and invoke a function with named parameters.
ocaml:
Multiple parameters can share a name. In the function definition colons are used to rename the parameters for use in the function body.
let add_xs ~x:x1 ~x:x2 = x1 + x2;;
add_xs ~x:3 ~x:7;;
named parameter default value
How to make named parameters optional by providing a default value in the definition.
ocaml:
For a named parameter to be optional, it must be following by an unnamed parameter in the definition. This permits the parser to unambiguously determine if the optional parameter has been provided or not. If the optional parameter is not followed by an unnamed parameter in the definition, then named parameter is not optional. If the function is invoked without the parameter, it returns a curried version of the function which expects the missing named parameter as an argument.
infix operator in prefix position
How to invoke an infix operator in prefix position.
function in infix position
How to invoke a function in infix position.
currying
How to create a curried function by providing values for some of the arguments of a function.
function composition operator
An operator which takes two functions as arguments and returns a function constructed from them by composition.
lazy evaluation
How to evaluate the arguments to a function in a lazy manner.
Lazy evaluation is also called callbyname.
ocaml:
OCaml provides the lazy function. It is up to the caller to specify that the argument is to evaluated lazily.
haskell:
Haskell evaluates arguments lazily by default.
strict evaluation
How to evaluate arguments before they are passed to a function.
Strict evaluation is also called call byvalue.
haskell:
The seq function evaluates its first argument and then returns the second argument.
Execution Control
if
if elseif else
sequencing
while
ocaml:
There is no break or continue statement. In addition to using references, it is possible to use exceptions to break out of a while loop.
for
How to loop over a range of integers.
sml:
How to define a for loop in SML:
datatype for = to of int * int
 downto of int * int
infix to downto
val for =
fn lo to up =>
(fn f => let fun loop lo = if lo > up then ()
else (f lo; loop (lo+1))
in loop lo end)
 up downto lo =>
(fn f => let fun loop up = if up < lo then ()
else (f up; loop (up1))
in loop up end)
How to use the for loop:
for (1 to 9)
(fn i => print (Int.toString i))
for (9 downto 1)
(fn i => print (Int.toString i))
for in reverse
How to iterate over a reversed range of integers.
list iteration
How to iterate over the members of a list.
loop
An infinite loop.
Exceptions
raise error
How to raise an error.
handle error
How to handle an error.
Concurrency
Filehandles
Files
Directories
Processes and Environment
Libraries and Namespaces
namespace example
namespaces
file name restrictions
import
namespace creation
namespace alias
namespace separator
subnamespace
inspect namespace
UserDefined Types
keywords used to define types by language  

pascal  c  c++  ocaml  scala  haskell  
type synonym  type  typedef  typedef  type  type  type 
sum type  type  enum or union  type  abstract class  data  
tuple product type  type  data  
record product type  record  struct  struct or class  type … of  class  data 
Examples of algebraic sum types are the enumerated type of Pascal and the enum of C. The definition of the type lists a set of values which variables which have the type can contain. The values are called variants.
The enumerated type of Pascal and the enum of C are implemented as integers, and one can recover the underlying integer value associated with each variant. In Pascal one uses the ord function to do this. One can use the equality test operator to determine whether two variables hold the same variant. One can also use the less than (<) operator to determine if a variable holds a variant which occurs earlier in the type definition list than another.
An enumerated type is thus similar to defining a sequence of integer constants like this:
typedef int month;
const month JANUARY = 1;
const month FEBRUARY = 2;
.
.
.
const month DECEMBER = 12;
An enumerated type gives the compiler the ability to ensure that only variants listed in the type definition list are actually stored in variables with the enumerated type however.
BETTER EXPLANATION AND MOTIVATION OF UNARY TYPES. OTHER THAN VARIANTS: UNIT. ARE
UNARY TYPES USEFUL?
Algebraic sum types are more general than enumerated types, because the variants are not restricted to being unary types. By a unary type we mean a type whose variables can only contain a single value. EXAMPLE OF SUCH AND ALGEBRAIC SUM TYPE. Because of this generality, one cannot assume that a general algebraic sum type variant has an integer representation. Some languages nevertheless define an order on the variants.
SUM TYPE: NUMBER OF VALUES IS THE SUM OF THE VALUES OF EACH OF THE VARIANTS
C UNION TYPE AS ALGEBRAIC SUM TYPE
Examples of algebraic product types are the record of Pascal and the struct of C. An algebraic product type wraps several values into a single "super" value. The components of an algebraic product type are called fields, and each has a type which constrains the values which can be stored in it. The type of each field is normally a preexisting type, but see the note on recursive types below.
To extract a field from a product value, each field must be identified. In the case of the Pascal and the C struct the fields are given names. Product types can also be defined in which the fields are identified by position like a tuple. OCaml and Haskell support both types of product type.
Since OCaml and Haskell have both tuples and tuple product types, it is worthwhile to consider the differences. One could represent represent coordinates on plane with a simple pair tuple with this type:
(float, float)
However, all 2tuples in which the components are both floats are the same type. With tuple product types, we could define two distinct types:
type cartesian = Cartestion of float * float;
type polar = Polar of float * float;
The compiler will now prevent us from using cartesian coordinates in a place where polar coordinates are expected.
It is also instructive to consider the difference between a type synonym and a product type with a single field. In the former case the two types are interchangeable. Type synonyms are useful as a shorthand for a long type, such as a 10tuple or a function type. Functions which operate on variables of the original type will also operate on variables with the type synonym. In fact, it should be noted that type synonyms don't create a constructor, so the constructor for the original type must be used.
A product type with a single field creates a new type and provides a constructor for it which accepts the original type as an argument. Functions which take the original type as an argument cannot be used on the new type.
COMBINED ALGEBRAIC TYPES.
Algebraic product types first appeared in 1966 in Algol W. Algol W extended Algol 60 by adding a record type. The idea was due to Niklaus Wirth and C. A. R. Hoare. Pascal, which appeared in 1970, had both a record type and an enumerated type as already noted, and the Pascal enumerated type seems to be the first example of a type that could be called an algebraic sum type.
Algebraic types first appeared in their full generality in the programming language called Hope, circa 1980. Algebraic types were soon borrowed into ML. Hope introduced the terms algebraic data type, product type, and sum type. It also introduced pattern matching.
PATTERN MATCHING.
type synonym
sum type
generic type
recursive type
Objects
Inheritance and Polymorphism
REPL
repl
repl limitations
repl last value
help
ocaml
The OCaml top level provides these directives:
#cd "DIRNAME";;
#directory "DIRNAME";;
#install_printer PRINTER_NAME;;
#label BOOL;;
#load "FILENAME";;
#print_depth N;;
#print_length N;;
#quit;;
#remove_printer PRINTER_NAME;;
#trace FUNCTION_NAME;;
#untrace FUNCTION_NAME;;
#untrace_all;;
#use "FILENAME";;
#warnings "WARNINGS_LIST";;
inspect type
load source file
search path
set search path on command line
SML
Programming in Standard ML '97
The Standard ML Basis Library
OCaml
F#
F# Language Reference
F# Core Library Reference