Functions in SML - Kansas State University

Defining Functions

Defining values of simple types

? val i = 3;

val i = 3 : i n t

Defining function values:

? v a l i n c = f n ( x ) => x + 1 ;

v a l i n c = f n : i n t ?> i n t

? inc (3);

val i t = 4 : i n t

? v a l i s 3 = f n x =>

i f x = 3 then ¡± y e s ¡± e l s e ¡± no ¡± ;

v a l i s 3 = f n : i n t ?> s t r i n g

? i s 3 4;

v a l i t = ¡± no ¡± : s t r i n g

Function types: fn: ->

Functions in SML

Amtoft

from Hatcliff

from Leavens

Defining Functions

Functions as Values

Multiple Arguments

Currying

Polymorphism

Fun with fun

Functions in SML

Amtoft

from Hatcliff

from Leavens

Defining Functions

The previous definitions can be abbreviated:

fun () = ;

? fun i n c ( x ) = x + 1 ;

v a l i n c = f n : i n t ?> i n t

? fun i s 3 x =

i f x = 3 then ¡± y e s ¡± e l s e ¡± no ¡± ;

v a l i s 3 = f n : i n t ?> s t r i n g

? fun t e s t ( x , y ) = i f x < y then y e l s e x +1;

v a l t e s t = f n : i n t ? i n t ?> i n t

Functions as Values

Multiple Arguments

Currying

Polymorphism

ML Programs

A (simple) ML program is generally a sequence of

function definitions

Functions in SML

Amtoft

from Hatcliff

from Leavens

Defining Functions

Functions as Values

fun push ( v a l u e , s t a c k )

...

...;

fun pop ( s t a c k )

...

...;

fun empty ( s t a c k )

...

...;

fun make?s t a c k ( v a l u e )

...

...;

Multiple Arguments

Currying

Polymorphism

Functions as Values

Functions in SML

Amtoft

from Hatcliff

from Leavens

Functions can be anonymous

? f n x => x + 2 ;

v a l i t = f n : i n t ?> i n t

Defining Functions

Functions as Values

Multiple Arguments

Currying

Functions can be tuple components

? v a l p = ( f n ( x , y ) => x + y ,

f n ( x , y ) => x ? y ) ;

v a l p = ( fn , f n ) :

( i n t ? i n t ?> i n t ) ? ( i n t ? i n t ?> i n t )

? #1(p ) ( 2 , 3 ) ;

val i t = 5 : i n t

? #2(p ) ( 2 , 3 ) ;

v a l i t = ?1 : i n t

Polymorphism

Functions in SML

Functions as Values

Amtoft

from Hatcliff

from Leavens

Functions can be list elements

? fun add1 ( x )

v a l add1 = f n

? fun add2 ( x )

v a l add2 = f n

? fun add3 ( x )

v a l add3 = f n

=

:

=

:

=

:

x +

int

x +

int

x +

int

1;

?> i n t

2;

?> i n t

3;

?> i n t

? v a l l s = [ add1 , add2 , add3 ] ;

v a l l s = [ fn , fn , f n ] : ( i n t ?> i n t ) l i s t

? hd ( l s ) ( 3 ) ;

val i t = 4 : i n t

? hd ( t l ( l s ) ) ( 3 ) ;

val i t = 5 : i n t

Defining Functions

Functions as Values

Multiple Arguments

Currying

Polymorphism

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download