Introduction to ML

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 declarations with 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 sources.cm a.sig b.sml c.sml Group is a.sig b.sml c.sml • % 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

SML/NJ Demo

Introduction to ML – Part 1