Control Flow

if / else

Conditions use word operators — eq, ne, lt, gt, lte, gte, combined with and, or, not. Blocks are indentation, no colons:

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age = 20

if age gte 18 and age lt 65
    log['working age']
else
    log['not working age']

working age

Chain conditions with else if (there is no elif keyword — it's just an if in the else branch):

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score = 72

if score gte 90
    log['A']
else if score gte 70
    log['B']
else
    log['C']

B

There is no ternary expression: use an if/else statement, and set the variable before it. A variable set inside a branch belongs to that branch and ends with it, so a value the rest of the program reads is set first and changed inside:

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n = 42
size = 'small'
if n gt 10
    size = 'big'
log[size]

big

Reading a variable after the branch that set it ended is refused before the program runs, with the line and this fix.

while

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i = 0
while i lt 3
    i = i + 1
log[i]

3

(No += in Crow — write i = i + 1. The compiler optimizes it the same.)

for

for iterates arrays and ranges:

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total = 0
for n in [1, 2, 3, 4]
    total = total + n
log[total]

10

But for is bigger than this in Crow: it's an expression that collects values, and when its body only computes, it runs its iterations in parallel on every core. That story deserves its own chapter, and it's chapter 6.

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doubled = for n in [1, 2, 3]
    n * 2
log[doubled]

[2, 4, 6]