Expressions and Statements
The grammatical workhorse of MillScript is the expression. Most
contexts expects either expressions or statements - which are merely
sequences of semi-colon separated expression. The main practical
distinctions are that
-
an empty sequence is legal but an empty expression is not - use a
pair of empty parentheses to denote an expression which delivers
no results;
-
only the last expression in a sequence may return results.
Which contexts require expressions and which require statements has
been decided on pragmatic grounds. One one hand we want our syntax
to be free of "red tape" and on the other we want some defence
against simple typing mistakes. The compromise is that expressions
are required when results are required - otherwise statements are
allowed. So the conditional-test of an if-expression is an
expression but the then & else parts are statements.
Simple expressions
Simple expressions, ones that lack unbracketed infix/postfix
operators, are required in a couple of places in MillScript. The
most important place is in the attribute of an embedded XML
expression, such as
<table border=<em>simple expression</em> />
These simple expressions may not contain infix operators - but since
any expression can be converted to a simple expression by
surrounding it with parentheses, this is not much of a limitation.
This means that if you want to compute the border of a table using
an arithmetic expression you will want to enclose it in parentheses
e.g.
