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Computing with ioLProgrammer's GuideLanguage Reference

abs tag   add tag   align field   and tag   array tag   audio tag   backgroundColor field   bold field   border field   borderBottom field   borderColor field   borderLeft field   borderRight field   borderStyle field   borderTop field   bottom field   box tag   button tag   carat field   checkBox tag   choiceBox tag   class tag   clear tag   clientFrame tag   color field   console tag   dialog tag   div tag   do field   ellipse tag   else field   eq tag   false tag   focus field   focusOrder field   font field   for tag   ge tag   gt tag   height field   hotKey field   if tag   img tag   inf tag   inline field   input tag   invalid tag   int tag   italic field   join tag   layer field   le tag   left field   limit field   line tag   lt tag   margin field   marginBottom field   marginLeft field   marginRight field   marginTop field   mod tag   mul tag   ne tag   neg tag   not tag   null tag   num tag   onClear field   onClick field   onCommit field   onContextClick field   onExit field   onFocus field   onGet field   onKeyDown field   onKeyPress field   onKeyUp field   onMouseDown field   onMouseIn field   onMouseMove field   onMouseOut field   onMouseUp field   onPull field   onPush field   onResize field   onTimer field   openLink tag   or tag   pivot field   playing field   put tag   putError tag   putLn tag   requestTransfer tag   right field   rotate field   scalar tag   scroll field   scrollPos field   selectable field   spacing field   spacingBottom field   spacingLeft field   spacingRight field   spacingTop field   span tag   split tag   sub tag   table tag   tabRow tag   then field   timer tag   top field   transfer tag   transferAbility tag   transition field   true tag   underline field   vector tag   video tag   visible field   void tag   width field   with field   xor tag


true tag

Category: ephemeral logic tag

Produces the true value, or tests for the true value against zero or more given values.

Sample usage

<true> — expresses the value true

<true 1,0,null,{true},true> — tests the values in the primary field and produces the resulting values: false,false,false,false,true. Although three of the values in the primary field would logically evaluate to true, only the last one is the value true itself.

Fields

Primary field

Category: vector field

Optional. The primary field may contain one or more values to test against.

Behavior

The true tag, when used without any field values, may be used to express the literal value true anywhere it is required.

When at least one primary field value is specified, the tag functions in a different way: it tests values for being exactly the value true

This is different from using the eq tag to check if a value is 'equals' true. Many values such as nonzero integers or non-empty strings of text are evaluated as being equal to true even if the values have different types, but the true tag tests for an exact match to the value true itself.

Example

In the following code, both the eq and true tags are used to compare a vector containing various values.

<v:vector 52.5,null,false,true>
- values are: <join delim={,} v></n>
- eq tag produces:
    <join delim={,} 
        <i:for 1 limit=v.# do=
            <eq true, <v.@ i>>
        >
    ></n>
- true tag produces: <join delim={,} | true v></n>

Although the false tag accepts multiple values and can produce a list of results, the eq tag only produces a single result of comparison, hence a for tag is used to test against each value. In both cases, the join tag is used to separate the values with commas so the list of values doesn't run together when pushed into the console.

The following appears in the console. The eq tag is used to test if each of the values logically and arithmetically equates to true even if they are different types, but the true tag imposes a stronger condition, requiring them to be of the same type.

- values are: 52.5,,false,true
- true tag produces: false,false,false,true
- eq tag produces: true,false,false,true

In this case the expression <eq true, 52.5> evaluates to true, but the expression <true 52.5> evaluates to false, hence the difference in output.