values.md

Values in expectations

The real world is messy. Egret supports various ways for an expectation to match a range of values.

For the related topic on matching property names / column names please see the munging article.

Strings:

Strings (text, names, labels) are have two options. They can either be:

• a normal string: hello, or "hello" (quoted) if special characters are used
  • must match exactly, other than by case (they are case-insensitive)
• or a regular expression: /bo+/
  • denoted by a forward slash at the start, and one at the end

Regular expressions allow us to match wildcards (and many other complex patterns). An example:

/^boo.*/ means match any text that starts with boo and will match

• boobook
• boobird
• booted eagle
• booby

A discussion on regular expressions are outside the scope of this article. See this guide for more help: https://regexone.com/.

Numerics:

In general any numeric field on a test, as well as all coordinates for events and segments will accept a variety of syntaxes, including:

• literal values: 1.0, 1, -1.23, 0.0023
• exponential notation: 4.56e3, -1E-6
• constants: ε , ∞ , -∞
• inequality relations: >, <, ≥, ≤
• tolerances: ±
• approximations: ~, ≈
• intervals: [x1, x2], (x1, x2], [x1, x2), (x1, x2)

This syntax allows for a wide range of concepts to be encoded in a dense format. We think this density makes large test-sets easy to work with.

A formal grammar for this syntax is defined interval.ebnf and is shown below.

However, the easiest method of working with this notation is to just look through the examples.

expression

References: number, tolerance, relation, interval, approximation

tolerance

Used by: expression References: number

Examples:

• 1.23±0.2 within 0.2 of 1.23
• 1.23±ε ➡ within epsilon (the smallest relevant value) of 1.23

relation

Used by: expression References: number

Examples:

• >1.23 ➡ greater than 1.23
• <1.23 ➡ less than 1.23
• ≥1.23 ➡ greater or equal to 1.23
• ≤1.23 ➡ less or equal to 1.23

approximation

Used by: expression References: number

Examples:

• ~1.23 ➡ loosely approximate (within an order of magnitude) to 1.23 ➡ (0.123, 12.3)
  • useful for logarithmic values
• ≈1.23 ➡ approximately equal to 1.23. Defined as within 5% of target value
  • ≈1.23 ➡ (1.16, 1.29)
  • ≈11025 ➡ (10473, 11576)

interval

Used by: expression References: number

Examples:

• [1.2, 1.3] ➡ a value that lies between 1.2 and 1.3, including endpoints ➡ 1.2 ≤ x ≤ 1.3
• [1.2, 1.3) ➡ a value that lies between 1.2 and 1.3, including min, excluding max ➡ 1.2 ≤ x < 1.3
• (1.2, 1.3] ➡ a value that lies between 1.2 and 1.3, excluding min, including max ➡ 1.2 < x ≤ 1.3
• (1.2, 1.3) ➡ a value that lies between 1.2 and 1.3, excluding endpoints ➡ 1.2 < x < 1.3

number

Used by: expression, tolerance, relation, approximation, interval References: constant, real

Any number, including our constants:

Examples:

• -1.23
• 1.23
• 0.0
• ∞

constant

Used by: number

Examples:

• ε ➡ the smallest representable value. This value is
  • 0.001 currently
  • variable in the app configuration
  • used to ignore floating point or rounding errors
  • can be used as a value itself, or more commonly as a threshold
  • think of it as computers are weird, it is close enough
• ∞ ➡ Positive infinity
• -∞ ➡ Negative infinity

real

Used by: number References: pos, neg, zero

pos

Used by: real, neg References: digit

neg

Used by: real References: pos

digit

Used by: pos