BAML supports five primitive types that form the foundation of the type system.
String
String types represent text data. BAML supports three string formats:
Quoted Strings
Inline strings surrounded by double quotes, similar to strings in most programming languages.
"Hello World"
"\n" // Escaped characters supported
Quoted strings cannot contain template variables or expressions. Use block strings for that.
Unquoted Strings
Simple inline strings without quotes, useful for configuration values.
Restrictions: Unquoted strings may not contain:
- Quotes (“double” or ‘single’)
- At-signs @
- Curlies
- Hashtags #
- Parentheses ()
- Brackets []
- Commas ,
- Newlines
Block Strings
Multi-line strings surrounded by #" and "#, automatically dedented and stripped of first/last newlines.
Block strings support Jinja templating:
template_string Greeting(name: string) #"
Hello {{ name }}!
"#
\n to include literal escape sequences.
Including "# in content: Prefix with more # symbols:
Integer (int)
Whole numbers without decimal points.
Represents whole numbers (positive, negative, or zero)
function DescribeCircle(radius: int) -> string {
client "openai/gpt-4o-mini"
prompt #"
Describe a circle with a radius of {{ radius }} units.
"#
}
Generated Types
# Type: int
radius: int = 5
Float (float)
Floating-point numbers with decimal precision.
Represents decimal numbers with floating-point precision
function CalculateArea(pi: float) -> string {
client "openai/gpt-4o-mini"
prompt #"
Calculate using pi as {{ pi }}.
"#
}
BAML supports implicit casting of int → float, but to explicitly ensure a float value, use 0.0 instead of 0.
Generated Types
# Type: float
pi: float = 3.14159
Boolean (bool)
True or false values.
Represents true/false values
function CreateStory(long: bool) -> string {
client "openai/gpt-4o-mini"
prompt #"
Write a story that is {{ "10 paragraphs" if long else "1 paragraph" }} long.
"#
}
test LongStory {
functions [CreateStory]
args { long true }
}
test ShortStory {
functions [CreateStory]
args { long false }
}
Generated Types
# Type: bool
long: bool = True
Null
Represents the absence of a value.
Represents a null/nil/None value
type NullableString = string | null
Generated Types
# Type: None
value: None = None
Combined Example
Using multiple primitive types together:
function DescribeCircle(radius: int | float, pi: float?, includeArea: bool) -> string {
client "openai/gpt-4o-mini"
prompt #"
Describe a circle with a radius of {{ radius }} units.
{% if includeArea %}
Include the area of the circle using pi as {{ pi or 3.14159 }}.
{% endif %}
What are some properties of the circle?
"#
}
test CircleDescription {
functions [DescribeCircle]
args {
radius 5.0
pi 3.14
includeArea true
}
}
Type Casting
Integers can be implicitly cast to floats
// This works - int is cast to float
function Example(value: float) -> string {
// ...
}
test TestCasting {
functions [Example]
args { value 5 } // 5 (int) is cast to 5.0 (float)
}
Order matters in union types. "1" will be parsed as:
int when type is int | stringstring when type is string | int