CS537 - Lecture Notes for 2000.03.22

By Christopher Cunningham

SML Basic Types

Type	Example	Operators
Unit	()
Bool	true, false	andalso, orelse, =, <>
Integers	75, ~10	basic math ops (+, -, *, div, mod) and relational ops (<, <=, >, >=, =, <>)
Strings	"xyz"	std. escape chars, relational ops
Reals	3.14, 21e7	real(conversion), basic math ops, relational ops except for = and <>, floor, ceiling
Char	#"a"	str(#"a") (conversion)

Type Constructors

Tuples

Fixed sequence of types (not a list)
Must have at least 2 values

(1,2) : int * int
("xyz", 1=2) : string * bool

Nested tuples

(1,2, (3, 4)) : int * int * (int * int)

Equality testing

(1, 2) = (0+1, 1+1) : true
(1,2,3) = (1, 2) : type error

Selecting single components

#2(4,3,2,1) : 3
#4(4,3,2,1) : 1
#5(4,3,2,1) : error

Lists

All elements must be of the same type
Example

[1,2,3,4,5] : int list

Operators

[] : empty list (can also use nil)
:: : cons

1::[] : [1]
1::2::[] : [1,2]

HD - head of list

HD[1,2,3,4] : 1

TL - tail of list

TL[1,2,3,4] : [2,3,4]

NULL - test for empty list
@ - append

[1,2,3] @ [4,5] : [1,2,3,4,5]

Records

Example

{a = 1, b = 2} : {a:int, b:int}

Element access

#field name
#b {a = 1 + 2, b = 3.0/4.0} : 3.0 / 4.0

Identifiers (two types)

Alphanumeric (excludes reserved words)

sequence of letters, digits, underscores, and tic's
must start with a letter or a tic
examples

'a (polymorphic)
a (regular expression)
a' (also a regular expression - the tic is just part of the id name)

Symbolic

any regular sequence of ! % @ $ + - / : > = < ? \ ~ ^ | # *
example

<==>
|=>

can't redefine + - * because they're overloadable

Comments

(* text *)

Creating New Identifiers

val id = expression
Basic examples

val x = 1

val x = 1 : int

val x = x + 1

val x = 2 : int (x has been rebound)

More complex examples (extended from above)

val z = (x, x, x)

val z = (2, 2, 2) : int * int * int

val l = [z, z]

val l = [(2,2,2), (2,2,2)] : (int * int * int) list

Using patterns in value declarations examples

Basic

val x = (1,2)
val (h,t) = x

val h = 1 : int, val t = 2 : int

More complex

val l = [1,2,3]
val [v1, v2, v3] = l

val v1 = 1 : int, val v2 = 2 : int, val v3 = 3 : int

val [1, x, 3] = l

val x = 2 : int

val [1, rest] = l

error, not the same length

val v1 :: rest = l

val v1 = 1 : int, val rest = [2,3] : int list

Using the wildcard character as a 'don't care

val _ :: rest = l

val rest = [2,3] : int list

Other notes for using patterns

cannot use the same identifier more than once in the pattern

val [x,x,x] = [1,1,1]

error, not a valid declaration

Introduction to Functions

Calling a function

Function-name args
Parenthesis are optional

fn args = fn (args) = (fn args)

examples

fct : call to function fn with no args
fct (x) : call to function fn with one arg
fct (x,y,z) : call to function fn with one arg also (treated as a tuple)