3 - Control flow

All typical control flow (for, while, if/else, do) are supported, and parenthesis around the condition are not necessary. Multiple conditions can be specified in the for loop, e.g.:`

for i=1:2,j=2:4
println(i*j)
end

break and continue are supported and works as expected.

Julia support list comprehension and maps:

  • [myfunction(i) for i in [1,2,3]]

  • [x + 2y for x in [10,20,30], y in [1,2,3]]

  • mydict = Dict(); [mydict[i]=value for (i, value) in enumerate(mylist)] (enumerate returns an iterator to tuples with the index and the value of elements in an array)

  • [students[name] = sex for (name,sex) in zip(names,sexes)] (zip returns an iterator of tuples pairing two or multiple lists, e.g. [("Marc","M"),("Anne","F")] )

  • map((n,s) -> students[n] = s, names, sexes) (map applies a function to a list of arguments) When mapping a function with a single parameter, the parameter can be omitted: a = map(f, [1,2,3]) is equal to a = map(x->f(x), [1,2,3]).

Ternary operator is supported as a ? b : c (if a is true, then b, else c). Put attenction to wrap the ? and : operators with space.

Logical operators

  • And: &&

  • Or: ||

  • Not: !

Not to be confused with the bitwise operators & and |.

Currently and and or aliases to respectively && and ||has not being imlemented.

Do blocks

Do blocks allow to define anonymous functions that are passed as first argument to the outer functions. For example, findall(x -> x == value, myarray) expects the first argument to be a function. Every time the first argument is a function, this can be written at posteriori with a do block:

findall(myarray) do x
x == value
end

This defines x as a variable that is passed to the inner contend of the do block. It is the task of the outer function to where to apply this anonymous function (in this case to the myarray array) and what to do with its return values (in this case boolean values used for computing the indexes in the array). More infos on the do blocks: https://en.wikibooks.org/wiki/Introducing_Julia/Controlling_the_flow#Do_block , https://docs.julialang.org/en/stable/manual/functions/#Do-Block-Syntax-for-Function-Arguments-1‚Äč

While an updated, expanded and revised version of this chapter is available in "Chapter 3 - Control Flow and Functions" of Antonello Lobianco (2019), "Julia Quick Syntax Reference", Apress, this tutorial remains in active development.