19.4 Record expression { $\,\langle$ lab ${}_{1}$ $\rangle\,$ = $\,\langle$ exp ${}_{1}$ $\rangle\,$ , $\ldots$ , $\,\langle$ lab ${}_{n}$ $\rangle\,$ = $\,\langle$ exp ${}_{n}$ $\rangle\,$ }

A record expression is a collection of pairs of labels $\,\langle$ lab ${}_{i}$ $\rangle\,$ and expressions $\,\langle$ exp ${}_{i}$ $\rangle\,$ .

A record expression is evaluated as follows. First, it is checked whether all of its labels are distinct. If not, a type error occurs. Second, each expression $\,\langle$ exp ${}_{i}$ $\rangle\,$ is evaluated to a type $\,\langle$ ty ${}_{i}$ $\rangle\,$ and value $v_{i}$ in the order of their occurrences in the record expression. Finally, they are sorted in the order of label strings and constitutes a record type

{ $\,\langle$ lab ${}_{1}^{\prime}$ $\rangle\,$ : $\,\langle$ ty ${}_{1}^{\prime}$ $\rangle\,$ , $\ldots$ , $\,\langle$ lab ${}_{n}^{\prime}$ $\rangle\,$ : $\,\langle$ ty ${}_{n}^{\prime}$ $\rangle\,$ }

and record value

{ $\,\langle$ lab ${}_{1}^{\prime}$ $\rangle\,$ = $v_{1}^{\prime}$ , $\ldots$ , $\,\langle$ lab ${}_{n}^{\prime}$ $\rangle\,$ = $v_{n}^{\prime}$ }

as the type and value of the record expression.

Therefore, for example, when

val x = {SML = (print "SML#";"SML#"), IS = (print " is ";" is "), SHARP = (print " sharp!\n";" sharp!\n")}

is evaluated, it prints "SML# is sharp!" and then x is bound to the type and value like the following

val x = {IS = " is ", SHARP = " sharp!\n", SML = "SML#"} : {IS: string, SHARP: string, SML: string}