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Values

Values

A Value is the basic structure datatype in Nu.

pub struct Value {
    pub value: UntaggedValue,
    pub tag: Tag,
}

Where the value field is any given value type UntaggedValue and the tag field holds metadata associated with it.

An UntaggedValue covers the following value types:

pub enum UntaggedValue {
    Primitive(Primitive),
    Row(Dictionary),
    Table(Vec<Value>),

    Error(ShellError),

    Block(Evaluate),
}

Where Primitive is:

pub enum Primitive {
    Nothing,
    Int(BigInt),
    Decimal(BigDecimal),
    Bytes(u64),
    String(String),
    Line(String),
    ColumnPath(ColumnPath),
    Pattern(String),
    Boolean(bool),
    Date(DateTime<Utc>),
    Duration(u64),
    Range(Box<Range>),
    Path(PathBuf),
    Binary(Vec<u8>),

    // Stream markers (used as bookend markers rather than actual values)
    BeginningOfStream,
    EndOfStream,
}

Let's look at these in reverse order to see how Primitives build towards our full Value types:

Primitive

A Primitive data type is a fundamental type in Nu. While these have similarities to the fundamental datatypes of programming languages, there are a few differences because of the shell capabilities of Nu.

Nu comes with two 'big' number types: BigInt for integers and BigDecimal for decimal numbers. This allows Nu in the future to do mathematical operations and maintain precision for longer.

Other data types that are perhaps a bit different from the norm:

  • Nothing = An empty value
  • Bytes(u64) = filesize in number of bytes
  • Line(String) = A string value with an implied carriage return (or cr/lf) ending
  • ColumnPath(ColumnPath) = A path to travel to reach a value in a table
  • Pattern(string) = a glob pattern (like the nu* in ls nu*)
  • Duration(u64) = A count in the number of seconds (like 1hr in ls | where modified < 1hr)
  • Range(Box<Range>) = A range of values (like 0..2 in ls | range 0..2)
  • Path(PathBuf) = a filepath
  • Binary(Vec<u8>) = an array of bytes
  • BeginningOfStream = a marker to denote the beginning of a stream
  • EndOfStream = a marker to denote the end of a stream

UntaggedValue

In addition to the primitive types, Nu supports aggregate data types. Collectively, these aggregate types are called UntaggedValues.

Currently, Nu supports 5 UntaggedValue types: Row, Table, Block, Primitive, and Error.

Tables and Rows

Nu uses a set of terms that match a bit more closely to spreadsheets. Rather than having lists of objects, Nu has a table, which contains rows. Each Row contains the column names and their corresponding Values.

Blocks

Blocks represent code that is ready to be executed by the evaluator. One example of this is the condition in where {$it > 10}.

Errors

Represents errors that can happen when pipelines are run.