#lang scribble/manual

@title{Indentation}

Pyret enforces indentation. A valid piece of code will not run if it is not
indented properly. Most of the time, this will not be a problem, since the
majority of expressions can be typed in just one line. Some syntaxes, such
as @tt[]{fun} and @tt[]{if}, require multiple lines, which must follow one
of two indentation rules.

The first rule is same-line/greater-column (SLGC). Two pieces of code obey
this rule when the second piece of code is either on the same line as the
first, or is indented at least 2 spaces. For example, both

@verbatim|{
fun plus1(x): x + 1
}|

and

@verbatim|{
fun plus1(x):
  x + 1
}|

are well-indented. However,

@verbatim|{
fun plus1(x):
x+1
}|

is not well-indented, and will result in an error. The documentation
of each syntactic form specifies all indentation rules that it follows.

The second rule is same-line/same-column (SLSC). Either the two pieces
of code must be on the same line, or they must be indented by the same
amount. For example, in an @tt[]{if} statement, all branches must
be lined up at the same level:

@verbatim|{
fun sgn(x):
  if x < 0: -1
  elif x = 0: 0
  else: 1
}|