This was one of theopen projects.

There are two ways of enabling the indentation syntax. One is to use the-i compiler option. This enables it for all the files passedto the compiler.

The other is to use#pragma indent at the top of the file(comments and whitespace before are OK, anything else is NOT!).

We maintain a stack of indentation strings. Whenever a new, non-empty lineis processed we check if:

• its indentation is the same as the one on the top of the stack, in which case we add a semicolon to close the previous line
• otherwise the indentation has the top-one as prefix, in which case we push it on the stack and add an open brace
• otherwise, if the new indentation is somewhere on the stack, we pop elements looking for it and generate a close brace for each indentation popped
• otherwise it is an error

When the line ends with backslash, in which case it is effectively mergedwith the next one.

When the line ends with ; or the next one begins with {, the ; is not added.

Inside [], () and {} the indentation processing is off.

Most of the comments inPython: Myths about Indentation also applies to our indentation syntax.

using System.Console[Qux] \class FooBarpublicstatic Main () :void    WriteLine ("Hello")static Foo (x :int) :voidif (x ==3)def y = x*42      Foo (x)else      [x].Map (fun (x) {        x*2      })static Bar () :intdef foo =2 \+7 \*13    foo

is translated to:

using System.Console;[Qux]class FooBar {publicstatic Main () :void {    WriteLine ("Hello")  }static Foo (x :int) :void {if (x ==3) {def y = x*42;      Foo (x)    }else {      [x].Map (fun (x) {        x*2      })    }  }static Bar () :int {def foo =2+7*13;    foo  }}

If you use alternative clauses in a match,to match multiple cases to one result,

match (s) {  |"a"  |"aa" =>1  |"b"  |"bb" =>2  |_ =>0}

in indententation based syntax :

match (s)  |"a"  |"aa" =>1  |"b"  |"bb" =>2  |_ =>0

it won't compile, you need to use line continuation ('\')

match (s)  |"a" \  |"aa" =>1  |"b" \  |"bb" =>2  |_ =>0

or just use standard syntax with { .. } for this specific match:

match (s) {  |"a"  |"aa" =>1  |"b"  |"bb" =>2  |_ =>0}