First Look at ML - Modern Programming Languages - Lecture Slides, Slides of Advanced Computer Programming

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A First Look at ML

Chapter Five Modern Programming Languages, 2nd ed. (^) Docsity.com 1

ML

 Meta Language

 One of the more popular functional

languages (which, admittedly, isn’t saying

much)

 Edinburgh, 1974, Robin Milner’s group

 There are a number of dialects

 We are using Standard ML, but we will just

call it ML from now on

Chapter Five Modern Programming Languages, 2nd ed. (^) Docsity.com 2

Outline

 Constants

 Operators

 Defining Variables

 Tuples and Lists

 Defining Functions

 ML Types and Type Annotations

Chapter Five Modern Programming Languages, 2nd ed. (^) Docsity.com 4

Chapter Five Modern Programming Languages, 2nd ed. 5

val it = 1234 : int

• 123.4; val it = 123.4 : real

Integer constants: standard decimal , but use tilde for unary negation (like ~1 )

Real constants: standard decimal notation Note the type names: int , real

Chapter Five Modern Programming Languages, 2nd ed. 7

• "fred"; val it = "fred" : string
• "H"; val it = "H" : string
• #"H"; val it = #"H" : char

String constants: text inside double quotes Can use C-style escapes: \n , \t , \ , " , etc.

Character constants: put # before a 1-character string Note type names: string and char

Outline

 Constants

 Operators

 Defining Variables

 Tuples and Lists

 Defining Functions

 ML Types and Type Annotations

Chapter Five Modern Programming Languages, 2nd ed. (^) Docsity.com 8

Chapter Five Modern Programming Languages, 2nd ed. 10

• "bibity" ^ "bobity" ^ "boo"; val it = "bibitybobityboo" : string
• 2 < 3; val it = true : bool
• 1.0 <= 1.0; val it = true : bool
• #"d" > #"c"; val it = true : bool
• "abce" >= "abd"; val it = false : bool

String concatenation: ^ operator Ordering comparisons: < , > , <= , >= , apply to string , char , int and real

Order on strings and characters is lexicographic

Chapter Five Modern Programming Languages, 2nd ed. 11

val it = false : bool

• true <> false; val it = true : bool
• 1.3 = 1.3; Error: operator and operand don't agree [equality type required] operator domain: ''Z * ''Z operand: real * real in expression: 1.3 = 1.

Equality comparisons: = and <>

Most types are equality testable: these are equality types Type real is not an equality type

Chapter Five Modern Programming Languages, 2nd ed. 13

• true orelse 1 div 0 = 0; val it = true : bool

Note: andalso and orelse are short-circuiting operators: if the first operand of orelse is true, the second is not evaluated; likewise if the first operand of andalso is false

Technically, they are not ML operators, but keywords All true ML operators evaluate all operands

Chapter Five Modern Programming Languages, 2nd ed. 14

• if 1 < 2 then #"x" else #"y"; val it = #"x" : char
• if 1 > 2 then 34 else 56; val it = 56 : int
• (if 1 < 2 then 34 else 56) + 1; val it = 35 : int

Conditional expression (not statement) using if … then … else … Similar to C's ternary operator: (1<2)? 'x' : 'y' Value of the expression is the value of the then part, if the test part is true, or the value of the else part otherwise There is no if … then construct

Chapter Five Modern Programming Languages, 2nd ed. 16

val it = 2 : int

• 1.0 * 2.0; val it = 2.0 : real
• 1.0 * 2; Error: operator and operand don't agree [literal] operator domain: real * real operand: real * int in expression: 1.0 * 2

The ***** operator, and others like + and < , are overloaded to have one meaning on pairs of integers, and another on pairs of reals ML does not perform implicit type conversion

Chapter Five Modern Programming Languages, 2nd ed. 17

• real(123); val it = 123.0 : real
• floor(3.6); val it = 3 : int
• floor 3.6; val it = 3 : int
• str #"a"; val it = "a" : string Builtin conversion functions: real ( int to real ), floor ( real to int ), ceil ( real to int ), round ( real to int ), trunc ( real to int ), ord ( char to int ), chr ( int to char ), str ( char to string )

You apply a function to an argument in ML just by putting the function next to the argument. Parentheses around the argument are rarely necessary, and the usual ML style is to omit them

Chapter Five Modern Programming Languages, 2nd ed. 19

• square 2+1; val it = 5 : int
• square (2+1); val it = 9 : int

Function application has higher precedence than any operator Be careful!

Practice

Chapter Five Modern Programming Languages, 2nd ed. 20

What if anything is wrong with each of these expressions? trunc 5 ord "a" if 0 then 1 else 2 if true then 1 else 2. chr(trunc(97.0)) chr(trunc 97.0) chr trunc 97.