For Expression

# simple for
for Var in Seq
        ForBody

# for with filter
for Var in Seq if Cond
        ForBody

Parenthesis can be used

# simple for
for (Var in Seq)
        ForBody

# for with filter
for (Var in Seq if Cond)
        ForBody

The for expression allows to write loops in a way that is familiar to people coming from mainstream languages.

The expression is another way of writing a list comprehension but allowing a sequence of expressions in the body and not only one expression.

The expression collects the values of the ForBody and returns them as a list.

Examples:

R0 = for X in lists.seq(1, 10)
    A = X + 1
    A

Result:

R0 = [2,3,4,5,6,7,8,9,10,11]

R1 = for X in lists.seq(1, 10) if X % 2 == 0
    X + 1

Result:

R1 = [3,5,7,9,11]

R2 = for X in lists.seq(1, 5)
    for Y in lists.seq(6, 10)
        (X, Y)

Warning

The expression lists.seq(6, 10) in the inner for will be evaluated 5 times if it’s a costly expression you should assign it to a variable outside the for and use it.

Result:

R2= [[{1,6},{1,7},{1,8},{1,9},{1,10}],
     [{2,6},{2,7},{2,8},{2,9},{2,10}],
     [{3,6},{3,7},{3,8},{3,9},{3,10}],
     [{4,6},{4,7},{4,8},{4,9},{4,10}],
     [{5,6},{5,7},{5,8},{5,9},{5,10}]]

R3 = for (X, Y) in lists.zip(lists.seq(1, 3), lists.seq(4, 6))
    (Y, X)

Result:

R3 = [{4,1},{5,2},{6,3}]