4.1.3. Constructs¶

4.1.3.1. Conditional ¶

Code	Meaning
if (expression) action	One logical condition expressible as an action (e.g. print) or on a single line (e.g. x = a) i.e. no multi-line blocks are allowed
if (expression) then ! block else if (expression) then ! block else ! block end if	Multiple logical conditions
block_a: if (expression) then ! block else if (expression) then block_a block_b: if (expression) then ! block end if block_b else then block_a ! block end if block_a	Named Blocks for nested blocks
select case(number) case (:0) ! block case (1:2) ! block case (3) ! block case (4:) ! block default ! block end select	Select - choose an action depending on the value of `number` (an integer) `case (:0)` \(\Rightarrow\) `number` is \(\le\) 0 `case (1:2)` \(\Rightarrow\) `number` is 1 or 2 `case(3)` \(\Rightarrow\) `number` is 3 `case(4:)` \(\Rightarrow\) `number` is \(\ge\) 4 `default` \(\Rightarrow\) `number` is none of the above
where (mask expression) ! block elsewhere ! block end where	Where - useful for iterating through arrays with a conditional statement without using a loop

Code	Meaning
do i = i_start, i_stop, i_step ! block end do	Iterator - loops with an integer counter until stop is reached
do while (expression) ! block end do	Do-While - loops with condition tested at start
do if (expression) exit ! block end do	Blank Do - loops without condition until the if statement is true
outer: do inner: do i = i_start, i_stop, i_step if (expression) cycle inner ! block if (expression) exit outer ! block end do inner end do outer	Nested Do - contains outer and inner loops `outer: do` \(\Rightarrow\) Outer “blank” do loop `inner: do i = start, stop, step` \(\Rightarrow\) Inner “iterator” do loop `if (expression) cycle inner` \(\Rightarrow\) Repeat inner loop according to expression `if (expression) exit outer` \(\Rightarrow\) Exit outer loop according to expression Notice the use of named loops to distinguish between them, i.e. “outer” and “inner” are names of loops

Code	Meaning
stop	Halts the program cleanly
stop 'message'	Halts the program cleanly displaying a message
return	Leaves a subroutine or function
exit	Leaves a loop
cycle	Next iteration
continue	Used in a do loop, which would otherwise end in an if (archaic)
go to 100	Jumps to the specified statement number (archaic). The number it refers to must be within columns 1 - 5.