Null object: Difference between revisions

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COMMENT using the UNESCO/IFIP/WG2.1 ALGOL 68 character set

result := °;

IF REF STRING(result) :≠: ° THEN print(("result ≠ °", new line)) FI;

IF REF STRING(result) :?: ° THEN print(("result ? °", new line)) FI;

END COMMENT

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=={{header|Haskell}}==

Haskell does not have a universal null value. There is a 'value of every type', the undefined value (sometimes written ⊥, 'bottom'), but it is essentially a sort of exception — any attempt to use it is an error.

Haskell does not have a universal null value. There is a 'value of every type', the undefined value (sometimes written ?, 'bottom'), but it is essentially a sort of exception — any attempt to use it is an error.

<lang haskell>undefined -- undefined value provided by the standard library

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if ![info exists arr(nullval)] ...

if ![dict exists $dic nullval] ...</lang>

You can algo use this condition inside an if statement to check if the variable $value is set or not:

<lang Tcl>[expr {([string compare "$value[puts \"\"]" ""]==1)}]</lang>

I think this is the better way to achieve it. In this case, if $value is set, returns true, or else returns false.

{{omit from|TI-83 BASIC}} {{omit from|TI-89 BASIC}}