Functional Design and Programming

Lecture 8:

Imperative programming

Literature

Paulson, chap. 8 Reference types (8.1-8.3) References in data structures (8.4-8.6) Input/Output (8.7-8.9)

Exercises

Paulson, chap. 8: 8.1-8.4, 8.6-8.9 8.10-8.11, 8.13-8.15, 8.26-8.32 (8.16-8.19, 8.21-8.25)

.

References

References model storage locations References make imperative programming possible

in SML Referential transparency: Evaluation of an

expression can be repeated without change in result Referential transparency is broken by the use of

references.

Environment

Environment: Bindings of values to identifiers.

Bindings are established by: declarations (val, fun, exception; type, structure,

signature, functor) parameter passing (actual argument bound to

formal parameter) pattern matching

Store

Store: Mapping of (storage) locations to values; locations are values.

The store is updated by reference operations.

Example

val x = 5val cond = falseval iref = ref 25val rref = ref (ref (ref 8.5))

Environment and store

5

false

8.5

25

Store:Environment:

x:

cond:

iref:

rref:

Environment and store...

5

false

8.5

25

Store:Environment:

x:

cond:

iref:

rref:

l1

l2

l3

l4

l2

l4 l3

l1

Reference operations

Create a new reference: ref v Look up value of a reference: !r Update a reference: r := v Check if two references are equal: r = r’

Imperative Arrays

Imperative arrays have constant-time element lookup and update operations.

Example: val a = Array.array (10000, 0)

Array.update (a, 1800, 25);Array.sub (a, 1800)

String Processing

toString functions: Return string representation of argument.

Examples:Int.toString 5Bool.toString falseReal.toString 5.25

String Processing...

fromString functions: Scan input string for longest prefix that is representation of a given type.

Examples:Int.fromString “85”Int.fromString “85Xdyf”Int.fromString “Xdvydf”Real.fromString “5.25”Real.fromString “5.25odxx”Real.fromString “Xdfkdfj”

String Splitting...

String.tokens: Splitting strings into tokens, resp. fields

Example:

String.tokens Char.isSpace “ABC DE F G”

Substrings

Substring: Structure for operations on substrings of strings

Examples:Substring.splitl Char.isAlphaNum (Substring.all “a1B. dfjk “)

fun dateFromString...

Readers

Reader type: type (‘a, ‘b) reader = a -> (‘b * ‘a) option

‘a: source type ‘b: result type (`a, char) reader: character source

Example: List.getItem: ‘a list -> (‘a * ‘a list) option

Scanning functions

scan: Takes a character source and returns value denoted by longest prefix of a given type, together with remaining characters

Example:Real.scan List.getItem (explode “5.25”)

TextIO

See SML/NJ Basis library: Imperative I/O and Text I/O

HTML

HTML: HyperText Markup Language Used to specify formatted documents Prevalent in WWW documents Standard scenarios:

‘static’ HTML page on WWW-server, requested by WWW-client (browser)

function (‘servlet’) on WWW-server, invoked by browser, produces HTML-page

rendered by browser (in both cases)

HTML as Output Format

Idea: Leave layout and rendering to existing tools; generate input document format for those tools

Examples: HTML PostScript

HTML: Example

<P><EM>Westmoreland</EM>. Of fighting men they have full three score thousand.<P><EM>Exeter</EM>. There’s five to one;besides, they all are fresh.<P><EM>Westmoreland.</EM> O that we nowhad here <BR>But one ten thousand of those men in England <BR>That do no work to-day!

Translating to HTML

Inddata:Westmoreland. Of fighting men they have full three score thousand.

Exeter. There’s five to one;besides, they all are fresh.

Westmoreland. O that we now had here But one ten thousand of those men in England That do no work to-day!