The function convert( expr, 'truefalse' ) attempts to convert the expression expr to one of the two values true and false. This is intended to be used in composition with procedures that return a boolean literal that can include the value FAIL. The value FAIL is replaced by the value false.

The argument expression expr must be an expression that can be evaluated as a boolean, resulting in one of the values true, false, or FAIL. If $\mathrm{evalb}\left(\mathrm{expr}\right)$ returns true, then the conversion also returns the value true. Otherwise, the conversion returns the value false.

$\mathrm{convert}\left(\mathrm{true}\,'\mathrm{truefalse}'\right)$

$\mathrm{true}$

$\mathrm{convert}\left(\mathrm{false}\,'\mathrm{truefalse}'\right)$

$\mathrm{false}$

$\mathrm{convert}\left(\mathrm{FAIL}\,'\mathrm{truefalse}'\right)$

$\mathrm{false}$

$\mathrm{convert}\left(2<3\&comma;'\mathrm{truefalse}'\right)$

$\mathrm{true}$

$\mathrm{convert}\left(a<b\&comma;'\mathrm{truefalse}'\right)$

Error, (in `convert/truefalse`) unable to convert a < b to type `truefalse'

$\mathrm{sort}\left(\left[\mathrm{posint}\&comma;\mathrm{integer}\&comma;\mathrm{numeric}\&comma;\mathrm{string}\right]\&comma;\mathrm{subtype}\right)$

$\left[\mathrm{string}\&comma;\mathrm{posint}\&comma;\mathrm{integer}\&comma;\mathrm{numeric}\right]$

$\mathrm{sort}\left(\left[\mathrm{posint}\&comma;\mathrm{integer}\&comma;\mathrm{numeric}\&comma;\mathrm{string}\right]\&comma;\mathrm{rcurry}\left(\mathrm{convert}\&comma;'\mathrm{truefalse}'\right)\circ \mathrm{subtype}\right)$

$\left[\mathrm{string}\&comma;\mathrm{posint}\&comma;\mathrm{integer}\&comma;\mathrm{numeric}\right]$