1.1.3 Printing an expression

An unadorned expression is also a legal Yorick statement; Yorick prints its value. In the preceding examples, only the characters you would type have been shown; to exhibit the print function and its output, I need to show you what your screen would look like -- not only what you type, but what Yorick prints. To begin with, Yorick prompts you for input with a > followed by a space (see section 1.3.5 Prompts). In the examples in this section, therefore, the lines which begin with > are what you typed; the other line(s) are Yorick's responses.

> E 8.199e-07 > print, E 8.199e-07 > m;c;m*c^2 9.11e-28 3.e+10 8.199e-07 > span(0,2,5) [0,0.5,1,1.5,2] > max(sin(theta)*exp(-theta/6)) 0.780288

In the span example, notice that an array is printed as a comma delimited list enclosed in square brackets. This is also a legal syntax for an array in a Yorick statement. For numeric data, the print function always displays its output in a format which would be legal in a Yorick statement; you must use the write function if you want "prettier" output. Beware of typing an expression or variable name which is a large array; it is easy to generate lots of output (you can interrupt Yorick by typing control-c if you do this accidentally, see section 1.3.1 Starting, stopping, and interrupting Yorick).

Most non-numeric objects print some useful descriptive information; for example, before it was closed, the file variable above would have printed:

> file write-only text stream at: LINE: 201 FILE: /home/icf/munro/damped.txt

As you may have noticed, printing a variable and invoking a procedure with no arguments are syntactically indistinguishable. Yorick decides which operation is appropriate at run time. Thus, if file had been a function, the previous input line would have invoked the file function; as it was not a function, Yorick printed the file variable. Only an explicit use of the print function will print a function:

> print, fma builtin fma()