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Calling Sequence
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Conditional Function
ifelse(conditional expression, true expression, false expression)
`if`(conditional expression, true expression, false expression)
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Description
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The ifelse(c,a,b) function requires three arguments and returns the evaluation of the second or third, depending on the truth value of the first.
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The first argument a must be a conditional expression; if it evaluates to true, b is evaluated and returned. If a evaluates to false or FAIL, then c is evaluated and returned.
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The name `if` is an alias for ifelse. When using this name, if must be enclosed in back quotes (left single quotes) because if is a Maple reserved word.
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Conditional Expressions
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A conditional expression is any Boolean expression formed using the relational operators ( <, <=, >, >=, =, <> ), the logical operators (and, or, not), and the logical names (true, false, FAIL).
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When a conditional expression is evaluated in this context, it must evaluate to true, false, or FAIL; otherwise, an error occurs.
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Thread Safety
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The ifelse function is thread-safe as of Maple 15.
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Examples
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Simple Case
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The conditional operator can be used inside an equation. Since b (5) is not less than a (3), the result of the inner ifelse command will be the false expression, b, which is used as part of the calculation.
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Using ifelse with NULL
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Since a is less than b, x is assigned NULL. Unlike every other function call, which removes NULLs from the calling sequence, NULL can be used with the ifelse operator.
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>
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