Purpose & Structure
Conditionals, or if-statements, are used to evaluate truth conditions. Truth conditions were introduced in the previous session in connection with while- and repeat-loops. With loops, truth conditions serve as stop conditions. With if-statements, truth conditions serve to branch the procedural execution of code. The syntactic frame of conditionals is pretty close to natural language use: If something is the case do this, else do that. The 'something is the case'-part is a condition which can be true or false. Depending on the truth value of the condition, the 'do this' or the 'do that'-part is executed. This is meant by 'branching': You provide several branches and you define conditions to tell the script which branch to take. Any if-statement ends with
endif to tell the script where to continue with the normal procedural execution.
if condition is true code block else code block endif
else section is optional:
if condition is true code block endif
In this case, the condition is evaluated; if it is true the code block is executed and the script continues after
endif; if it is false the code block is ignored and the script continues after
With the optional
elsif, it is possible to evaluate more than one condition:
if first condition is true code block elsif second condition is true code block elsif third condition is true code block else code block endif
The order of conditions
Conditions are evaluated from top to bottom. The first condition that is true triggers the following code block to be executed, then the script jumps to
endif and continues. If all conditions are false the code block following
else is executed (if it is available).
That's all there is to the syntax of if-statements, so we are ready for a legit example:
# query minimum of selected pitch object pitch_floor = Get minimum: 0, 0, "Hertz", "Parabolic" # do something if minimum pitch is less than 130 Hz if pitch_floor < 130 speaker$ = "male" endif
The condition pitch_floor < 130 is evaluated. If it is true, the code block (only one statement in the example) is executed. If it is false, nothing happens and the script continues after
endif. Let's add female voices:
pitch_floor = Get minimum: 0, 0, "Hertz", "Parabolic" if pitch_floor < 130 speaker$ = "male" elsif pitch_floor < 220 speaker$ = "female" endif
Suppose pitch_floor is 100, which is less than 130 as well as less than 220. What's the value of speaker$ at the end of the if-statement? It's male, because, as I said before, Praat aborts evaluation and exits the if-statement (i.e. jumps to
endif) as soon as one condition is true. Obviously, the first true condition is 100 < 130.
If you use elsif-sections you have to pay attention to the order of conditions!
If pitch_floor is 175, speaker$ has the value female, because the first condition (175 < 130) is false but the second (175 < 220) is true. If pitch_floor is 245, speaker$ is undefined, because both conditions are false. So, let's add kids:
if pitch_floor < 130 speaker$ = "male" elsif pitch_floor < 220 speaker$ = "female" else speaker$ = "child" endif
Now, speaker$ contains child whenever the pitch_floor is greater than 220.
A summary of the few rules concerning if-statements:
- A minimal if-statement consists of the reserved word
if, a condition, a code block, and the reserved word
endifare allowed only once per if-statement
- any number (including 0) of
elsifsections are permitted
- 0 or 1
elsesection is allowed
You see, the syntactic structure of conditionals is pretty simple. Nonetheless, they are important and powerful tools. To make the most of conditionals it is essential to understand and exploit the potential of truth conditions, that's why we'll take a closer look at truth conditions in the next section. Of course, this topic is also relevant for while- and repeat loops.Next: Remarks on Conditions