Data Model

Fenl operates on typed values. Fenl's type system describes several different kinds of values.

Simple values such as the string "hello" or the integer 57 are scalar types. Zero or more scalar values of the same type may be part of a collection, such as a list, map, or set. Value types may be combined to create composite value types such as records.

Scalars

Scalar types include bool, number, and string.

Collections

Collection types include list and map. Each collection contains 0 or more elements of the same
type. A collection type describes the kind of collection, and the type of elements it contains.

Composites

Composite types allow combining multiple different types into a single value. Records are unnamed - any two records with the same set of fields and values are considered equal. Fields within a record may have different types. Field names must start with a letter.

Nullable Types

Value types may be either nullable or non-nullable. A nullable type allows any value from the base type as well as the value null. Nullable types are distinguished by having a trailing question mark in the type description.

Type Coercion

Fenl implicitly coerces numeric types when different kinds of numbers are combined. For example adding a 64-bit signed integer value to a 32-bit floating point value produces a 64-point floating point value.

Type Promotion Rules

Type coercion will never produce an integer overflow or reduction in numeric precision. The coercion rules can be summarized with the following rules:

1. Integers can be widened: i8 -> i16 -> i32 -> i64.
2. Unsigned integers can be widened: u8 -> u16 -> u32 -> u64.
3. Floating point numbers can be widened: f16 -> f32 -> f64.
4. Unsigned integers can be promoted to the next wider integer u8 -> i16, u16 -> i32, u32 -> i64.
5. All numbers may be converted to f64.
6. Strings may be implicitly converted to timestamps by attempting to parse them as RFC3339 values. The timestamp will be null for strings that don't successfully parse.

Numeric Type Coercion Table

When two numbers are used, Fenl attempts to promote them to a compatible type as the smallest type that both types may be converted to.
The following table shows the result of this promotion for pairs of numeric types.

ℹ

️ Coercion to Floating-Point

Note that when u64 is combined with a signed type the result is f64. This is the only case where an operation between integers produces a floating-point value.