Principles of Programming Languages and Systems

by
Peter Fritzson,
PELAB - Programming Environment Laboratory
Dept. of Computer and Information Science,
Linköping University, Sweden

Lecture 1

Control abstractions

Basic abstractions (p 6)

Assignment statement

x = 555

x = x+300

Structured abstractions (p 7-9)

If-statement

If[x>800,
  numSolns = 2;
  Print["hejsan"]
,
  numSolns=4;
  Print["hoppsan"]
]

While-statement

n = 9; 
While[n != 0,
  Print[n];
  n = Floor[n/2]
]

For-loop

For[i=1, i < 4, i++,
  Print[i]
]

Functional programming (p 12-14)

Conventional function style (p 13)

gcd[u_,v_] := Block[{
},
  If[v==0,
    Return[u]
  ,
    Return[gcd[v,Mod[u,v]]]
  ]
];

gcd[8,18]

Shorter version (Scheme-like, p 13)

gcd[u_,v_] := 
  If[v==0,
    u
  ,
    gcd[v, Mod[u,v]]
  ];

gcd[8,16]

Rule version (p 14)
(recurrence equations)

gcd[u_,0]  := u;

gcd[u_,v_] := gcd[v, Mod[u,v]];

gcd[8,28]

BNF and Abstract Syntax

Simple BNF grammar (p 70)

2-rule grammar

expr-- > expr + expr |
         number

Abstract syntax intermediate form (p 72-73)

Textual input form, evaluated value

3 + 4 * 5

Abstract syntax intermediate form
(Hold prevents evaluation)

Hold[3 + 4 * 5] //FullForm