Introduction to ML – Part 1

Kenny Zhu

Assignment 2 http://www.cs.princeton.edu/courses/archive/fall07/cos441/assignments/a2.htm

Due next Monday (Oct 1st)

Introduction to ML This lecture: some basics on the SML language and how to interact with the SML/NJ run time system

Next lecture: implement more complex system using SML

Resources: Robert Harper’s “Programming in Standard ML” Peter Lee’s “Notes on using SML/NJ systems” SML/NJ Basis Library

http://www.standardml.org/Basis/index.html See course webpage for pointers and info about how to get the software

Standard ML Standard ML is a general-purpose functional programming language with type checking and type inference

Emphasizes applications of functions, not state changes and mutable data

Support for Complex data structures Memory management like Java Large projects with many modules Advanced type system for error detection

ML Highlights Interactive Language

Type in expressions Evaluate and print result Compile into binary as well

Strongly-typed language Every expression has a type Functions as values Certain errors cannot occur Polymorphic types provide flexibility

ML Highlights High-level programming features

Data types Pattern matching Exceptions Mutable data discouraged Modules and functors

Basic types and expressions Int: 3+5, 2*6, 100 div 2, 2-5, ~3 Real: 3.1415, 100.0/3.0, ~1.5 Char: #”!” String “abc”, “hello” ^ “ “ ^ “world”

Bool: true, false, (5>6), (3<>4), a andalso b, c orelse d

Unit: ()

Data structures Tuple: (“george”, 35) Record: {name = “george”, age = 35}

List: 1::(2::(3::(4::nil)))) 1::2::3::4::nil 1::2::3::4::[] (1::2::nil)@(3::4::nil) [1,2,3,4] 1::2::[3,4]

Declaration val x = 5 let val a = 4 val b = 2 in a + b end fun succ x = x + 1 exception SomeException <of string> type complex_num = (real * real) val n = (3.0, 5.5) datatype number = Int of int | Real of real val n1 = Real ~8.0

Functions fun f (x, y) = x * y fun f x y = x * y (curried form) fn (x:int, y:int) :int => x * y val f = fn x y => x * y fun f pat_1 = exp_1 | f pat_2 = exp_2 | f pat_3 = exp_2 | f _ = exp_default

Other Useful Expressions if x>0 then x-1 else x+1 case num of Int x -> x div 2 | Real y -> y / 2.0

(expr_1; expr_2; …; expr_n) raise SomeException “Fatal Error” some_expr handle SomeExpection s =>

print s

When your program grows… Interactive mode is a good way to start learning and to debug programs, but…

Type in a series of declarations into a “.sml” file

- use “foo.sml”[opening foo.sml]…

list of declarationswith their types

Larger Projects SML has its own built in interactive “make”

Pros: It automatically does the dependency analysis for you

No crazy makefile syntax to learn Cons:

May be more difficult to interact with other languages or tools

Compilation Manager

% sml

- OS.FileSys.chDir “~/courses/510/a2”;

- CM.make(); looks for “sources.cm”, analyzes dependencies

[compiling…] compiles files in group

[wrote…] saves binaries in ./CM/

- CM.make’ “myproj/”(); specify directory

sources.cmc.sml

b.sml

a.sig

Group isa.sigb.smlc.sml

SML/NJ Demo