empg.icn: Program to make expression-evaluation programs

This program produces a program for evaluating Icon expressions.  The
input to this program has three forms, depending on the first character
of each line:

     :       the remainder of the line is an expression to be evaluated
             only once

     %       the remainder of the line is part of a declaration

     #       the remainder of the line is a comment and is ignored

Anything else is an expression to be evaluated in a loop.

For example, the input

# Time record access
%record complex(r, i)
:z := complex(1.0, 3.5)
z.r

produces a program to time z.r in a loop.
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The following options are supported:

     -l i    use i for the number of loop iterations, default 100000
     -d i    use i for the "delta" to adjust timings; otherwise it
               is computed when the expression-evaluation program
               is run