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# Factorio Prototype Docs Version 2.0.7

## NoiseExpression :: string or bool or double Example code

A boolean or double as simple values or a string that represents a math expression. The expression parser recognizes five basic token types (with their regex):

- Whitespace: `[ \n\r\t]*`

- Identifier: `[a-zA-Z_][a-zA-Z0-9_:]*` (e.g. cat_bar123)

- Number: `(0x[0-9a-f]+|([0-9]+\.?[0-9]*|\.[0-9]+)(e-?[0-9]+)?)` (e.g. `3.2`, `100`, `.6`, `4.2e-5`, `0x2a5f`). Supports hexadecimal input and scientific notation for decimal numbers.

- String: `("[^"]*"|'[^']*')` (e.g. `"cat bar 123"`, `'control-setting:copper-ore'`)

- Operator: See the list below

Identifiers are used to name functions and variables. The built-in functions and variables are documented in the auxiliary docs. Mods can define their own noise expressions which can be used as variables and functions. The entry points for this are NamedNoiseFunction and NamedNoiseExpression as well as local functions and expressions.

All functions accept both named and positional arguments. To differentiate between these function calls, positional arguments start/end with `(`/`)` and named arguments with `{`/`}`, e.g. `clamp(x, -1, 1)` and `clamp{min = -1, max = 1, value = x}` are the same function call. Because of this, positional arguments can't be mixed with named arguments. A function can't have more than 255 parameters.

The following operators are available, ordered by precedence:

- `x^y`: Exponentiation (fast, inaccurate), equivalent to the built-in `pow(x, y)` noise function

- `+x`, `-x`, `~x`: Unary plus and minus and unary bitwise not

- `x*y`, `x/y`, `x%y`, `x%%y`: Multiplication and division, modulo and remainder.

- `x+y`, `x-y`: Addition and subtraction

- `x<y`, `x<=y`, `x>y`, `x>=y`: Less than, less than or equal, greater than, greater than or equal

- `x==y`, `x~=y`, `x!=y`: Equal to and not equal to (Lua and C++ syntax)

- `x&y`: Bitwise and

- `x~y`: Bitwise xor

- `x|y`: Bitwise or

Modulo is implemented as `x - floor(x / y) * y` and remainder uses C++ `fmod(x, y)` function.

The boolean operators (less than, less than or equal, equal, not equal, greater than, greater than or equal) take two numbers and return 0 for false or 1 for true.

The bitwise operators convert single-precision floating-point numbers to signed 32-bit integers before computing the result.

## Examples

    "distance_from_nearest_point{x = x, y = y, points = starting_positions}"

    "clamp(x, -1, 1)"

Type used in

- AutoplaceSpecification::probability_expression
- AutoplaceSpecification::richness_expression
- AutoplaceSpecification::local_expressions
- NamedNoiseExpression::expression
- NamedNoiseExpression::local_expressions
- NamedNoiseFunction::expression
- NamedNoiseFunction::local_expressions
- NoiseFunction::expression
- NoiseFunction::local_expressions