Programming Language Concepts (CIS 635)

Programming Language Concepts (CIS 635)

Elsa L Gunter

4303 GITC

NJIT, www.cs.njit.edu/~elsa/635

http://www.cs.njit.edu/~elsa/635









Copyright 2002 Elsa L. Gunter

SML

• Compiler is on the AFS system at

/usr/local/sml/bin/sml

• A (possibly better, non-PowerPoint) text version of this lecture can be found at

www.cs.njit.edu/~elsa/635/SML_Lect/sml-shell

• For the SML code for today’s lecture see

www.cs.njit.edu/~elsa/635/SML_Lect/intro.sml


WWW Addresses for SML

• http://www.cs.njit.edu/~elsa/635/110-smlnj.exe• ftp://ftp.research.bell-labs.com/dist/smlnj/release/110/

110-smlnj.exe

• http://cm.bell-labs.com/cm/cs/what/smlnj/index.html

• http://cm.bell-labs.com/cm/cs/what/smlnj/doc/basis/pages/sml-std-basis.html

http://www.cs.njit.edu/~elsa/635/110-smlnj.exe











ftp://ftp.research.bell-labs.com/dist/smlnj/release/110/110-smlnj.exe

ftp://ftp.research.bell-labs.com/dist/smlnj/release/110/110-smlnj.exe

http://cm.bell-labs.com/cm/cs/what/smlnj/index.html


Books on SML

• Supplemental texts (not required)

– Elements of ML Programming, by Jeffrey D. Ullman, on Prentice Hall

– ML for the Working Programmer, by Lawrence C. Paulson, on Cambridge University Press


Session in SML

Standard ML of New Jersey, Version 110.0.7, September 28, 2000 [CM&CMB]

- (* Read-eval-print loop; expressions and declarations *)

- 2 + 3;

val it = 5 : int

- val test = 3 < 2;

val test = false : bool


SML Expressions and Declarations

- (*= At top-level, an expression= <exp>;= is treated as an abbreviation for the

declaration = val it = <exp>;=*)- "Hi there";val it = "Hi there" : string


SML Top-level Expressions and Declarations

- (* ^ is string concatenation *)

- it ^ " my good friend";

val it = "Hi there my good friend" : string

- (* () pronounced "unit" is the result for functions that don’t have a result *)

- print "Hello world\n";

Hello world

val it = () : unit


Overloading for Basic Arithmetic

- val x = 5 + 7;

val x = 12 : int

- val y = x * 2;

val y = 24 : int

- val z = 1.35 + 0.23;

val z = 1.58 : real


Overloading but No Coercion

- val w = y + z;stdIn:51.1-51.14 Error: operator and

operand don't agree [tycon mismatch]

operator domain: int * int operand: int * real in expression: y + z


Using SML Code From a File

• File named test.sml contains

3 + 2;

val x = 5 + 7;

val y = x * 2;

val z = 1.35 + 0.23;

val w = y + z;


- use "A:\\SML_Lect\\test.sml";

[opening A:\SML_Lect\test.sml]

val it = 5 : int

val x = 12 : int

val y = 24 : int

val z = 1.58 : real

Compiler Output


A:\SML_Lect\test.sml:5.1-5.14 Error: operator and operand don't agree [tycon mismatch]

operator domain: int * int

operand: int * real

in expression:

y + z

Compiler Output


Booleans (aka Truth Values)

- true;

val it = true : bool

- false;

val it = false : bool

- if y > x then 25 else 0;

val it = 25 : int


Booleans

- 3 > 1 andalso 4 > 6;

val it = false : bool

- 3 > 1 orelse 4 > 6;


- not (4 > 6);



Functions

- fun plus_two n = n + 2;val plus_two = fn : int -> int- plus_two 17;val it = 19 : int- val plus_two = fn n => n + 2;val plus_two = fn : int -> int- plus_two 14;val it = 16 : int


Values fixed at declaration time

- val x = 12;

val x = 12 : int

- fun plus_x y = y + x;

val plus_x = fn : int -> int

- plus_x 3;

val it = 15 : int


Values fixed at declaration time

- val x = 7;

val x = 7 : int

- plus_x 3;

val it = 15 : int


Functions with more than one argument

- fun add_three (x:int) y z = x + y + z;

val add_three = fn : int -> int -> int -> int

- val t = add_three 6 3 2;

val t = 11 : int


Partial application of functions

- val h = add_three 5 4;

val h = fn : int -> int

- h 3;

val it = 12 : int

- h 7;

val it = 16 : int


Functions as arguments

- fun thrice f x = f (f (f x));val thrice = fn : ('a -> 'a) -> 'a -> 'a- thrice plus_two;val it = fn : int -> int- it 4;val it = 10 : int- thrice (fn s => "Hi! " ^ s) "Good-bye!";val it = "Hi! Hi! Hi! Good-bye!" : string


Recursive Functions

- fun factorial 0 = 1= | factorial n = n * factorial (n - 1);val factorial = fn : int -> int- factorial 5;val it = 120 : int-- (* fun is needed for recursion

function declarations *)


Tuples

- val s = (5,"hi",3.2);

val s = (5,"hi",3.2) : int * string * real

- val (a,b,c) = s;

val a = 5 : int

val b = "hi" : string

val c = 3.2 : real


Tuples

- val d = ((1,4,62),("bye",15),73.95);

val d = ((1,4,62),("bye",15),73.95) : (int * int * int) * (string * int) * real

- val (p,(st,_),_) = d;

val p = (1,4,6) : int * int * int

val st = "bye" : string


Tuples

- fun fst_of_3 (x,_,_) = x;val fst_of_3 = fn : 'a * 'b * 'c -> 'a- s;val it = (5,"hi",3.2) : int * string * real- fst_of_3 s;val it = 5 : int- fst_of_3 d;val it = (1,4,62) : int * int * int


Records

- val teacher = {Name = "Elsa L. Gunter", ss = (119,73,6244), age = 102};

val teacher = {Name="Elsa L. Gunter",age=102,ss=(119,73,6244)}

: {Name:string, age:int, ss:int * int * int}


Records

- val {ss = (s1,s2,s3), Name = elsa, age = years} = teacher;

val elsa = "Elsa L. Gunter" : string

val years = 102 : int

val s1 = 119 : int

val s2 = 73 : int

val s3 = 6244 : int


Records and Tuples

- val q = (280,{student = {Name = "Joseph Martins",

= ss = (325,40,1276),

= age = 19},

= instructor = teacher});


Records and Tuples

val q = (280, {instructor={Name="Elsa L.

Gunter",age=102,ss=(119,73,6244)}, student={Name="Joseph

Martins",age=19,ss=(325,40,1276)}}) : int * {instructor:{Name:string, age:int, ss:int * int *

int}, student:{Name:string, age:int, ss:int * int *

int}}


Tuples are Records

- val strange = (1,"f",2) = {3 = 2, 2 = "f", 1 = 1};;

val strange = true : bool

Documents

Programming Language Concepts (CIS 635)