Tutorial 2

Exercise 1

Part 1

1. Expression and variable must have compatible types.
2. Disadvantages: types help detect programming error; helps with program design

Part 2

ghci> "CS2" ++ "PLD"
"CS2PLD"
-- [Char]
ghci> True || False
True
-- Boolean
ghci> 42*42
1764
-- Num a => a
ghci> sqrt 2
1.4142135623730951
-- Floating a => a

Exercise 2

Part 1

1. Refer to slides; 4 types
2. Efficiency; no time needed for allocation / deallocation; address is set during compile time

Part 2

We don’t know how many times we are going to recurse so we don’t know how much memory we need to use yet.

Exercise 3

1. Refer to slides; 2 types; static -> variables defined before execution; dynamic -> depends on the calling sequence
2. Dynamic is lenient but gets messy

Exercise 4

Part 1

Static: 5 Dynamic: 10

Part 2

global
g
global

g
# UnboundLocalError: local variable 'x' referenced before assignment

Exercise 5

let x = 3
f z = z + x in let x = True in f 6
-- output: 9
 
-- let x = True defined for the scope of "f 6"
-- but f has already captured x

let x = 3; f z = z + x in f 6
-- output: 9
 
-- same output as this removes a redundant instruction

With dynamic scope:

• first will error as Haskell tries to add a boolean to a number
• second will be 9

Exercise 6

Static; skipped Q.

Exercise 7

1. Changing the flow of execution / jump to different part of the program
2. Default initialise primitive type values. Do not initialise any local variables but allow them to be referenced. C does not allow jumps to the middle of a program.