1. LING/C SC/PSYC 438/538
Lecture 5
Sandiway Fong

2. Today’s Topics Sorting: Homework 4 Review More Perl:
fc (fold case), hash sort
Homework 4 Review
More Perl:
Implicit Coercion
Conditionals
Loops
On Thursday: Homework 5
first programming homework

3. Last Time: Arrays: insertion and deletion from the ends
Generalized form:
shift/unshift 1 2
n-2
n-1
pop/push
Perl functions may have side effects and also return values
Good ex: print "a", "\n";

4. Perl Arrays Sorting: {$a cmp $b} {$a <=> $b}
default (ASCII table order)
{$a <=> $b}
numeric
flip $a $b for reverse order
enable function fc for Unicode casefolding

5. Handling characters beyond ASCII …
Unicode encoding (utf-8)

6. Handling characters beyond ASCII …
Note:
open pragma
most general solution

7. Perl Hashes Sorting with a hash Usage:
sort byage keys %age
Let's sort fruits by color, ascending, descending…

8. Homework 4 Review Relevant tags: Stanford Parser: I made her duck
Phrasal:
S Sentence; NP Noun Phrase; VP Verb Phrase
Part of Speech (POS):
PRP Personal Pronoun; VBD Verb Past; PRP$ Possessive Personal Pronoun; NN Common Noun; . .
Dependency links:
nsubj; nmod:poss; dobj

9. Homework 4 Review
Lisp S-EXP syntax:
Tree representation:

10. Homework 4 Review ❌? cf. I baked [ John] [a cake] ❌ Verb: duck
❌ Ditransitive verb: duck

11. Homework 4 Review Winograd’s SHRDLU system: Tree Representation:
Move the red block on top of the smaller green one
Tree Representation:
PP modifies VP (not NP)

12. Homework 4 Review Another interpretation: Stanford parse:

13. Homework 4 Review

14. Implicit Coercion Example: Example:
Perl features implicit coercion of data types
Example:
the following program prints Equal!
== is the numeric equality comparison operator
my $one_string = "1";
my $one_number = 1;
if ($one_string == $one_number) {
print "Equal!\n"
} else {
print "Different!\n" }
Example:
the following program prints
3 is my number
. is the string concatenation operator
= qw(one, two, three);
my $string is my number";
print "$string\n";

15. Implicit Coercion print "4" * 4 16
print "4" x 4 (“x” is the repetition operator)
4444
@a = (4) x 4 (in list context)
(4, 4, 4, 4)

16. Conditionals and Looping
if < 10 ) { print “Small array\n” } else {print “Big array\n” }
here is a scalar = size of array
unless > 10) { print }
Note: if size of array a is ≤ 10, it prints the contents of array a

17. Conditionals and Looping

18. Conditionals and Looping
Looping over arrays
%fruits = qw(apple green orange orange lemon yellow);
foreach $f (keys %fruits) { print $f, " => ", $fruits{$f}, "\n” }
gives output:
lemon => yellow
apple => green
orange => orange
Note: keys %fruits = ("lemon", "apple", "orange") is an array

19. ARGV
Command line:
perl argv.perl 1 2 3

20. General Looping