Syntax and Blocks

This chapter explains the surface structure of XE programs: statements, blocks, indentation, and a few rules that make code parse correctly.

Statements end at the newline

XE is line-oriented. In most cases, one statement lives on one line.

x = 10
print(x)

The parser treats the newline as the end of the statement unless it is still inside parentheses or brackets.

Blocks use indentation

XE does not use braces. A block starts after a block header and is defined by indentation.

if true:
    print("inside the block")

print("outside the block")

The indented line belongs to the if block. The final line does not.

Why XE still uses :

Indentation tells XE where the block starts and ends.

The colon tells XE that the block header is complete and a block is about to begin.

while count < 5:
    count = count + 1

This makes block-introducing statements easier to read and simpler to parse consistently.

Spaces vs tabs

XE expects indentation to be consistent. The lexer accepts spaces and also counts a tab as four spaces, but mixed or inconsistent indentation can raise an invalid indentation compiler error.

Best practice:

• use spaces
• keep one indentation width everywhere in the file
• do not mix indentation styles inside the same block structure

Block-introducing forms

These statements start a block:

• if condition:
• elif condition:
• else:
• repeat count times:
• while condition:
• for name in iterable:
• fun name(args):
• struct Name:
• try: / catch name:

Use pass for a block that does nothing.

Comments

XE uses # for single-line comments.

# This line is ignored
count = 3  # this trailing text is also ignored

There is no multi-line comment syntax right now.

Parentheses and brackets

Parentheses are used for function calls and grouping:

print((10 + 20) * 2)

Brackets are used for lists and indexing:

items = [10, 20, 30]
print(items[1])

Imports

import helpers                  # use helpers.square(3)
import helpers as h             # use h.square(3)
from helpers import square      # use square(3)
from helpers import square as sq

Imports are top-level statements. They must appear before executable top-level code in the file.

What XE does not support in syntax yet

These are not part of the language right now:

• const declarations
• multi-line strings
• list comprehensions

Next steps

• Continue with Types and Values
• Then read Control Flow