Programming in SML

1
Programming in SML
2
Standard ML

• A functional language originally proposed by
  Robin Milner
• Many implementations / compilers / interpreters
  exist for the language
• We will be using the SML/NJ (Standard ML of New
  Jersey) interpreter

3
Why SML?

• Polymorphic type inference
• Pattern matching
• The real reason
• Because it's awesome!

4
Well then...

• Let's write some code....

5
Dynamic vs Static Typing

• In Scheme we didn't specify the types of data
  items
• In Java we do specify the type
• The two languages have completely different
  approaches to assigning types to data items

6
Dynamic vs Static Typing (cont)

• Dynamic typing (Scheme) do not determine the
  type of a variable/binding until runtime
• Static typing (Java) determine the type of a
  variable/binding at compile-time
• Which is better?

7
Why SML? (revisited)

• In SML, we didn't specify types either, is it
  statically or dynamically typed?

8
Type Inference

• SML is statically typed, but all types are
  inferred by the context of the code.
• Recall fun foo x x 3 SML will assign x to
  be of type int.
• Why? How

9
Tuples

• A tuple in SML is just like the mathematical
  construct of the same name
• An ordered sequence of objects that is finite in
  size
• (2, 5, 10, 18, 75)
• (adam, drinks, beer, sometimes)
• (word, 23, 3.14159)

10
Lists

• Just like most functional languages, SML has
  strong native support for lists of items
• Lists in SML are homogeneous
• All elements must be the same type
• Ex
• 1,2,3,4
• adam, plays, Xbox

11
Lists vs Tuples

• What's the difference?

12
Lists vs Tuples

• Lists can only contain items of the same type
• Tuples can contain items of different types