Syntax Basics

Dorpn is an indentation-based language. There are no curly braces to open a block, no semicolons to end a statement, and no parentheses around conditions. A statement ends where the line ends, and a block is simply a group of lines that are indented further than the line that introduced them.

This page covers the rules that apply everywhere in the language: how a program is laid out, how indentation works, how to write comments, what names and keywords look like, and how to write literal values such as numbers and strings. Once these rules feel natural, the rest of the language builds on them.

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Program Structure

A Dorpn file is a list of statements that run from top to bottom. Variable declarations, function calls, if blocks and loops can all appear directly at the top level of the file, and they execute in the order they are written.

Function definitions are the one exception to this ordering. A function can be defined anywhere in the file, and it can be called from anywhere, including from lines that appear above the definition.

If a file defines a function named _Start, Dorpn calls it automatically once all top-level statements have finished. You never call _Start yourself. It is the natural place for the main logic of a program, while the top level is used for constants and setup.

print("before")
hello()                        # fine, even though hello is defined below

func hello() -> Unit:
    print("hi")

func _Start() -> Unit:
    print("start runs last")

print("after")

Running this program prints:

before
hi
after
start runs last

Notice that _Start ran last, after the top-level print("after"), even though it appears earlier in the file.

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Indentation

Blocks are created by indentation. A line that ends with a colon starts a block, and every line inside that block must be indented further than the line that started it.

tag age = 20

if age >= 18:
    print("adult")
    print("welcome")
print("this line is outside the block")

Each new level of indentation must be exactly 2 or 4 spaces deeper than the level before it. Any other amount is rejected. You are free to choose either 2 or 4 for your project, but it is best to pick one and use it everywhere.

When a block ends, the next line must return to a level that already exists. You cannot dedent to a position that was never used by an enclosing block.

if true:
    if true:
        print("two levels deep")
    print("back to one level")
print("back to zero")

Blank lines and comment-only lines are ignored, so you can use them freely to separate sections of your code.

Tabs are not supported

Indentation must be made of spaces. A tab character is counted as a single space, which is not a valid indentation step, so a tab-indented block produces an IndentError. If your editor inserts tabs when you press the Tab key, switch it to insert spaces instead.

Single-line branches

For if, elif and else, a block that contains one statement can be written on the same line as the colon:

if score > 90: print("excellent")
elif score > 50: print("passed")
else: print("try again")

Loops and functions always need a normal indented block.

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Comments

Dorpn supports two kinds of line comments and one kind of block comment. Comments are ignored by the compiler and exist only for human readers.

# A line comment starting with a hash

tag a = 1            # a comment after code

#[ A block comment.
   It can span many lines. ]#

Removed in v0.4.4: The -- single-line comment style has been removed. Writing -- now reports a clear error instead of being treated as a comment. Use # for line comments and #[ ... ]# for multi-line comments.

A block comment starts with #[ and ends with ]#. Block comments can be nested, which makes them convenient for temporarily disabling a piece of code that already contains a comment:

#[ disabled for now
print("a")
#[ an old note ]#
print("b")
]#

If a block comment is never closed, the compiler stops with a LexorError that tells you the line where the comment began. When you write a block comment on its own lines, put the closing ]# at the end of a line rather than in front of code.

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Names and Keywords

Names for variables and functions are built from letters, digits and underscores. A name cannot start with a digit, and names are case sensitive, so count and Count are two different names.

tag score = 10
tag _temp = 3
tag player_two = 7

Some words have a special meaning in the language. These are called keywords, and they cannot be used as names.

Keywords	Purpose
tag imm Const	Declaring variables
func return	Defining functions and returning values
if elif else	Conditions
loop keep halt skip	Loops and loop control
and or not fld	Word operators
true false	Boolean values
void	An empty statement that does nothing

The type names Int, Float, String, Bool, Int32, Float32 and Unit are also special. See the Types page for details.

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Literals

A literal is a value written directly in the code.

Literal	Type	Examples
Whole number	Int	0, 42, 1000
Decimal number	Float	3.14, 0.5, 2.0
Text	String	"Dorpn", "hello world"
Boolean	Bool	true, false

Negative numbers are written with a leading minus sign, as in -5. Strings are always written with double quotes. Single quotes are not used for strings in Dorpn.

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Strings and Escape Sequences

Inside a string, a backslash starts an escape sequence. It lets you write characters that are difficult or impossible to type directly.

Sequence	Meaning
\n	New line
\t	Tab
\r	Carriage return
\\	A single backslash
\"	A double quote
\033	The ESC character, used for terminal colors

print("Name:\tDorpn")
print("She said \"hello\"")
print("C:\\projects")

Name:	Dorpn
She said "hello"
C:\projects

The \033 sequence is an octal escape. It is mostly useful for printing colored text in a terminal, as in this example:

Const CYAN :String = "\033[96m"
Const RESET :String = "\033[0m"

print(CYAN + "colored text" + RESET)

If a backslash is followed by a character that has no special meaning, the backslash is dropped and the character is kept as it is.

Not every octal escape is supported: the \000 escape, for example, is reported as an error.

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Common Mistakes

1. Mixing tabs into indentation

A tab is not a valid indentation step. Configure your editor to insert spaces, and the error disappears.

2. Indenting by 3 spaces

Each level must be 2 or 4 spaces deeper. Three spaces, or five, or any other amount, is an IndentError:

if true:
   print("3 spaces")           # IndentError: must be 2 or 4 spaces

3. Forgetting the colon

Every line that opens a block, whether if, elif, else, loop, keep or func, must end with a colon:

if score > 50                  # SyntaxError: Expected ':'
    print("passed")

4. Leaving the block empty

A colon must be followed by an indented block. If nothing is indented below it, the compiler reports Expected indented block. Use void when you genuinely want a block that does nothing:

if debug:
    void

5. Writing semicolons out of habit

Dorpn does not need semicolons. A stray ; at the end of a line is skipped and does no harm, but it is not part of the language and should not be used.