• Running the REPL
• Variables
• Expression Statements
• Floating-point Numbers
• Multi-line Input
• Line Editing

Running the REPL

Running the Pyro binary without a script argument launches the REPL — an interactive environment where you can run Pyro statements directly, e.g.

>>> echo "hello world";
hello world

Pyro statements normally end with a semicolon, ;, but you can omit the semicolon after typing a single statement in the REPL, e.g.

>>> echo "hello world"
hello world

Hit Ctrl-D or type exit and hit return to end the REPL session.

Variables

You can define and use variables in the REPL, just like in a script, e.g.

>>> var value = 123
>>> echo value + 456
579

Expression Statements

As a convenience, if the input statement is an expression that evaluates to any value other than null, the REPL automatically prints the $debug() string for the value, e.g.

>>> "foo" + "bar"
"foobar"

This is equivalent to running:

>>> echo $debug("foo" + "bar")
"foobar"

Floating-point Numbers

You can use the REPL as a simple calculator, e.g.

>>> 1 + 2
3

If the value of the expression is a floating-point number, you might be surprised by the output, e.g.

>>> 0.1 + 0.1
0.20000000000000001

Pyro is showing you the $debug() output for the expression, and calling $debug() on a floating-point number rounds its value to 17 decimal digits of precision, then strips any trailing zeros after the decimal point. (17 is the minimum number of decimal digits required to guarantee that any two distinct 64-bit floats have distinct representations.)

This is a feature, not a bug — $debug() shows you the value you actually have, not the value you expected!

If you want a friendlier representation, you can echo the value instead, e.g.

>>> echo 0.1 + 0.1
0.2

echo calls $str() on its arguments before printing them. For floating-point numbers, $str() rounds the value to 6 decimal digits of precision, then strips any trailing zeros after the decimal point.

(Note that these are simply default precisions — you can print a floating-point number to any level of precision using the $fmt() or $print() functions.)

Multi-line Input

The REPL automatically handles multi-line input, e.g.

>>> "foo
··· bar"
"foo\nbar"

You can define functions and classes over multiple lines, e.g.

>>> def add(a, b) {
···     return a + b;
··· }
>>> add(1, 2)
3

Line Editing

The REPL supports the standard set of emacs-style line editing commands, e.g. Ctrl-A to move to the start of the line, Ctrl-E to move to the end of the line, etc.

You can scroll backwards and forwards through the line-editing history using the up/down arrow keys or, alternatively, Ctrl-P and Ctrl-N.