Statements

If/Else Statements

The if statement allows you to conditionally execute a block of code. The syntax is:

if ( condition ) statement

The condition is an expression that is evaluated and if it is true then the statement is executed. The statement can be a single statement or a block of statements enclosed in {}.

For example:

def x = 3
if (x > 2) println 'x is greater than 2'    // output: x is greater than 2
if (x > 2) {
  x++
  println 'x is greater than 2'
}
// output: 
// x is greater than 2

The if statement can also have an else clause that is executed if the condition is false:

if ( condition ) statement1 else statement2

For example:

def x = 3
if (x > 2) println 'x is greater than 2' else println 'x is not greater than 2'
// output: x is greater than 2
if (x > 4) {
  println 'x is greater than 4'
} else {
  println 'x is not greater than 4'
}
// output: x is not greater than 4

The else clause can itself be another if statement:

def x = 3
if (x > 4) {
  println 'x is greater than 4'
} else if (x > 2) {
  println 'x is greater than 2'
} else {
  println 'x is not greater than 2'
}
// output: x is greater than 2

Postfix If/Unless

As well as the standard if statement, Jactl also supports a statement modifier form of if where the if and the condition come after the statement to be executed:

statement if condition

For example:

def x = 3
println 'x is greater than 2' if x > 2
// output: x is greater than 2

This form of if is useful for making code more readable in some situations.

There is also an unless form that is the opposite of if:

statement unless condition

The statement is executed if the condition is false:

def x = 3
println 'x is not greater than 4' unless x > 4
// output: x is not greater than 4

Loop Statements

Jactl provides for, while, and do/until loops for iterating over a block of code.

For Loops

The for loop has two forms. The first form is the same as in Java and Groovy:

for ( initialiser ; condition ; increment ) statement

The initialiser is a statement that is executed once at the start of the loop. The condition is an expression that is evaluated before each iteration of the loop and the loop continues as long as the condition is true. The increment is a statement that is executed after each iteration of the loop.

For example:

for (int i = 0; i < 5; i++) { println i }

The second form of for loop is the "for-each" loop that iterates over a collection of values:

for ( variable in collection ) statement

The collection can be a List, Map, String, or a number. The variable is a variable that will be assigned the value of each element in the collection in turn.

For example:

for (i in [1,2,3]) { println i }
// Output:
// 1
// 2
// 3
for (c in 'abc') { println c }
// Output:
// a
// b
// c
for (i in 3) { println i }
// Output:
// 0
// 1
// 2

If the collection is a Map then the variable will be a two-element list containing the key and value of each entry in the map:

for (entry in [a:1, b:2]) { println entry }
// Output:
// ['a', 1]
// ['b', 2]

You can also use a multi-variable declaration to get the key and value in separate variables:

for ((key,value) in [a:1, b:2]) { println "$key -> $value" }
// Output:
// a -> 1
// b -> 2

While Loops

The while loop executes a block of code as long as a condition is true:

while ( condition ) statement

For example:

def i = 0
while (i < 5) { println i; i++ }
// Output:
// 0
// 1
// 2
// 3
// 4

Do/Until Loops

The do/until loop is similar to a do/while loop in other languages. It executes a block of code and then checks a condition to see if it should continue. The loop continues until the condition is true.

do statement until ( condition )

For example:

def i = 0
do { println i; i++ } until (i == 5)
// Output:
// 0
// 1
// 2
// 3
// 4

Break and Continue

The break and continue statements can be used to control the flow of a loop. The break statement will exit the loop immediately. The continue statement will skip the rest of the current iteration and start the next one.

For example:

for (i in 10) {
  if (i == 3) continue
  if (i == 5) break
  println i
}
// Output:
// 0
// 1
// 2
// 4

Do Expression

The do expression allows you to turn a block of statements into an expression. The value of the do expression is the value of the last statement in the block.

For example:

def x = do { def i = 3; def j = 4; i + j }
x      // 7

This is useful when you want to assign the result of a complex calculation to a variable:

def x = do {
  def sum = 0
  for (i in 10) {
    sum += i
  }
  sum
}
x      // 45

Eval Statement

The eval statement allows you to compile and execute a string of Jactl code at runtime. The string can be a simple expression or can be a series of statements. The value of the eval statement is the value of the last expression in the string.

For example:

eval('3 + 4')                              // 7
eval('def x = 3; def y = 4; x + y')        // 7

You can pass in a map of variables that the script can access:

eval('x + y', [x:3, y:4])                  // 7

The script can modify the values in the map:

def vars = [x:3, y:4]
eval('x += y', vars)                      // 7
vars                                      // [x:7, y:4]

Print Statements

The print and println statements are used to output values. The print statement outputs the value as a string. The println statement outputs the value as a string followed by a newline.

For example:

print 'abc'
print 'def'
println 'ghi'
// Output:
// abcdefghi

The print and println statements can take multiple arguments which are concatenated together with spaces in between:

def x = 3
println 'x is', x, 'and x*x is', x*x
// Output:
// x is 3 and x*x is 9

Die Statements

The die statement is used to terminate the execution of a script immediately. It can be used to report an error and exit.

For example:

def x = 3
die 'x is too big' if x > 2