Lecture 4 - Scope and Fruitful Functions

Essential Skills For Computational Biology

2020-06-16

Kevin Bonham, PhD

"Scope" is where references live

• A reference is a human-readable name for data or action
  • eg. a variable, argument, or function name
• All references have scope
  • sometimes the scope is "global" (available everywhere)
  • sometimes the scope is narrow (eg. inside a loop)
• In different scopes, the same name may reference different things

i = 3

for i in 1:5
    print(i, " ")
end

1 2 3 4 5

i

3

myvar = "Green eggs"
function ham(myvar)
    myvar = "ham"
    return myvar
end

ham (generic function with 1 method)

myvar

"Green eggs"

function decrement4()
    j = 4
    while j > 0
        print(j, " ")
        j = j - 1
    end
    return j
end
decrement4()

0

# copy to REPL
j = 4

while j > 0
    print(j, " ")
    j = j - 1
end

Fruitful functions and the perils of printing

• returned values are printed in the REPL
• printed values are not (necessarily) returned

function verbose(thing)
    println(thing)
    return thing
end

verbose (generic function with 1 method)

verbose(true)

true

verbose(1)
verbose(2)
verbose(3)

3

verbose("woah");

woah

A reminder: I make mistakes

• Several people have encountered tests that failed even though they had correct answers
• Don't bang your head against the wall (for too long)
• We will still make you work for it
• Not all difficulty is desirable

One other reminder: Helping eachother is ok

(Just don't copy-paste code from one another)

Final project ideas

• COVID data analysis
• SARS-CoV2 evolution / strain analysis
• Police violence data analysis
• Your idea here

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