Scripting Guide - SAS

Chapter 8 Programming Methods 189
Lists and Expressions
Evaluate expressions inside expressions
Eval Expr evaluates expressions inside other expressions but returns an expression that includes the results.
By comparison, Eval evaluates any expressions inside the expression, and then evaluates the expression.
Here is an example where you would need to evaluate the inner expression first:
// assumes a data table with column named X3
x = expr( distribution(column( expr("X"||char(i)) )) );
i = 3;
y=Eval Expr(x); // returns Distribution(Column("X3"))
However, Eval Expr only unpacks the inside layer then stops, returning the result as an expression. To
evaluate further, you need to either call the result in a subsequent step, or else put Eval() around the
EvalExpr().
// two-step method
y=Eval Expr(x);
y;
// one-step method
eval(eval expr(x));
See Table 8.3 “Compare all the operators for controlling evaluation,” p. 191, to learn what would happen if
you tried to use Eval directly on x without first doing Eval Expr.
Parsing strings into expressions, and vice versa
Parsing is the syntactic scanning of character strings into language expressions. Suppose that you have read
in a valid JSL expression into a character string, and now want to evaluate it. The Parse function returns
the expression. To evaluate it, use the Eval function.
x = parse("a=1") ; // x now has the expression a=1
eval(parse("a=1")); // a now has the value 1
To go in the reverse, use the Char function, which converts an expression into a character string. Usually the
argument to a Char function is an Expr function (or a NameExpr of a global variable), since Char evaluates
its argument before deparsing it.
y = char(expr(a=1)); // results in y having the character value "a=1"
z = char(42);
The Char function allows arguments for field width and decimal parameter if the argument is a number.
The default is 18 for width and 99 for decimal (Best format).
char(42,5,2);
// results in the character value "42.00"
To preserve locale-specific formatting in the numeric value, include the