5. Argument evaluation

Parameters in traditional programming languages are evaluated before the call: If the variable a has the value 10, then

print a

would print 10.

Shells (and Tcl) put implicit quotes around the arguments,, and you have to use an evaluate operator to undo the quoting. For example the operand xx$(a)yy is implicitly translated into (string_concat "xx" a "yy").

Implicit quoting is convenient when most arguments are constants, as in interactive use. Consider the alternative:

mv "-i" "foo.c" "foo.c.old"

One the other, implicit quoting is clumsy when there are other data types in addition to strings. For example in:

abs -10

we want to pass the integer -10 to the `abs' routine, not the string "-10".

Q's solution is to provide macros, similar to those in Lisp: A macro is a function that is run at compile time to transform an expression into a different expression. Q provides primitives that makes it convenient to write macros in user-oriented terms. These are discussed next.