meson.build

NAME

meson.build - a build system dsl

DESCRIPTION

The meson dsl is a dynamically typed language, similar to other interpreted languages like python and ruby. All objects are immutable. Functions cannot be defined, only built-in functions are available.

• STRUCTURE - overview of source and project layout
• TYPES - information on all primitive types
• SYNTAX - description of syntax and keywords

STRUCTURE

All meson projects must have a file called ‘meson.build‘ at the project root. This is the root build file. This file must have a call to the ‘project()‘ function as its first statement. Additional ‘meson.build‘ files may reside in any subdirectories of the project. These build files are then executed with the ‘subdir()‘ function.

TYPES

The meson build system dsl contains most of the common types that would be expected:

• booleans (written as ‘true‘ and ‘false‘)
• integers
• strings
• arrays
• dictionaries

Booleans

Booleans are either ‘true‘ or ‘false‘.

OPERATORS

• ‘and‘ - logical and
• ‘or‘ - logical or
• ‘not‘ - logical and

Integers

You can specify an integer literal using decimal, hexadecimal, octal, and binary.

int_1 = 1
int_42 = 42
int_255 = 0xFF
int_493 = 0o755
int_1365 = 0b10101010101

All common arithmetic operations are implemented for integers: addition, subtraction, division, multiplication, and modulo.

OPERATORS

• ‘*‘ - multiplication
• ‘/‘ - integer division
• ‘%‘ - modulo (remainder)
• ‘+‘ - addition
• ‘-‘ - subtraction
• ‘==‘ - equal to
• ‘!=‘ - not equal to
• ‘<‘ - less than
• ‘>‘ - greater than
• ‘<=‘ - less than or equal to
• ‘>=‘ - greater than or equal to

Strings

Strings in Meson are declared with single quotes. ‘‘ is the escape character.

The full list of escape sequences is:

• ‘\‘ Backslash
• ‘’‘ Single quote
• ‘a‘ Bell
• ‘b‘ Backspace
• ‘f‘ Formfeed
• ‘n‘ Newline
• ‘r‘ Carriage Return
• ‘t‘ Horizontal Tab
• ‘v‘ Vertical Tab
• ‘ooo‘ Character with octal value ooo, up to 3 digits long
• ‘xhh‘ Character with hex value hh
• ‘uxxxx‘ Character with 16-bit hex value xxxx
• ‘Uxxxxxxxx‘ Character with 32-bit hex value xxxxxxxx
• ‘N{name}‘ Character named name in Unicode database

Multi-line strings are surrounded by 3 consecutive quotes. These are raw strings that do not support the escape sequences listed above.

Format strings are expressed by a placing leading ‘f‘ before the first opening quote. Inside of a format string, sequences of the form ‘@[a-z_]+@‘ will be substituted with the value of the matching variable.

name = ’Alice’

# prints "Hello Alice"
message(f’Hello @name@’)

OPERATORS

• ‘+‘ - concatenate two strings
• ‘/‘ - concatenate two strings as if ‘join_paths()‘ was called
• ‘[n]‘ - access the character at index ‘n‘
• ‘==‘ - equal to
• ‘!=‘ - not equal to

Arrays

Arrays are delimited by brackets. An array can contain an arbitrary number of objects of any type.

OPERATORS

• ‘+‘ - If the rhs operand is an array, it will be joined to the lhs array. If it is a scalar, it will be appended to the lhs array.
• ‘[n]‘ - access the object at index ‘n‘
• ‘<obj> in <array>‘ - check if object ‘obj‘ is in ‘array‘
• ‘<obj> in <array>‘ - check if object ‘obj‘ is not in ‘array‘
• ‘==‘ - equal to
• ‘!=‘ - not equal to

Dictionaries

Dictionaries are delimited by curly braces. A dictionary can contain an arbitrary number of key: value pairs. Keys are required to be strings, but values can be objects of any type. Dictionaries are immutable and do not have a guaranteed order.

OPERATORS

• ‘+‘ - merge two dictionaries. In case of a conflicting key, the value from the rhs dictionary will be taken.
• ‘[key]‘ - access the object with key ‘key‘
• ‘<key> in <dict>‘ - check if key ‘key‘ is in ‘dict‘
• ‘<key> not in <dict>‘ - check if key ‘key‘ is not in ‘dict‘
• ‘==‘ - equal to
• ‘!=‘ - not equal to

SYNTAX

A meson build file is composed of statements, which are terminated by newlines. Other than the statement-terminating newline, white space has no syntactic meaning.

Comments

A comment starts with the ‘#‘ character and extends until the end of the line.

Variables

A variable can contain a value of any type, and does not need to be predeclared.

var1 = ’hello’
var2 = 102

One important difference in how variables work in the dsl is that all objects are immutable. When you see an operation which appears like a mutation, actually a new object is created and assigned to the name.

var1 = [1, 2, 3]
var2 = var1
var2 += [4]
# var2 is now [1, 2, 3, 4]
# var1 is still [1, 2, 3]

Function and method calls

Builtin functions are called by their name followed by parenthesis containing optional, comma-separated arguments. Arguments are either positional or keyword. Keyword arguments are expressed using the keyword without quotes, followed by a colon.

foo()
foo(’bar’)
foo(’bar’, baz: true)

Method calls are expressed by a ‘.‘ followed by the same function call syntax as above.

foo.bar()
foo.bar(’baz’, qux: false)

For a complete list of functions and methods, please see ‘meson-reference(3)‘.

If statements

Start an if statement with the ‘if‘ keyword followed by a boolean expression. Further conditions can be expressed using the ‘elif‘ keyword followed by a boolean expression. The ‘else‘ keyword can be used to handle the case when no conditions are matched. An if statement is terminated with the ‘endif‘ keyword.

if conditon1
elif condition2
else condition3
endif

Foreach statements

To loop over values in an iterable, use the ‘foreach‘ keyword followed by a comma separated list of names to assign the values of the iterable to, a colon, and an iterable expression. Only arrays and dictionaries are iterable. A foreach statement is terminated with the ‘endforeach‘ keyword.

Arrays have one value to assign to.

foreach value : array

foo(value)

endforeach

Dictionaries have one two values to assign to.

foreach key, value : dictionary

	foo(key)
	bar(value)

endforeach

Inside a ‘foreach‘ block you may use the ‘break‘ and ‘continue‘ keywords. ‘break‘ exits the loop immediately. ‘continue‘ skips the rest of the current iteration.

SEE ALSO

meson-reference(3) meson(1) muon(1)