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Value Types

Parameter values can include literals, equations, and imported functions. The main literal types are numbers, strings, and booleans.

Numbers

Numbers use familiar decimal notation: whole numbers, values with a decimal point, and scientific notation (e or E) when a value is very large or very small. inf can be used for infinity.

For example,

100th prime number: p_100 = 541
Golden ratio: phi = 1.618
Avogadro constant: N_A = 6.022e23
Infinity: inf_val = inf

Number Operators

Arithmetic (for ordinary scalar values):

  • ^ - exponentiation
  • * - multiplication
  • / - division
  • % - modulo
  • + - addition
  • - - subtraction

Comparisons (produce booleans; can be chained, e.g. 1 < 2 < 3):

  • < - less than
  • > - greater than
  • <= - less than or equal
  • >= - greater than or equal
  • == - equal
  • != - not equal

Built-in pi and e

The identifiers pi and e are built-in numeric constants (π and Euler’s number). They can be used like any other value in expressions.

Strings

Strings behave like fixed strings, not like growable text in many other languages. Typical uses include modes or categories. For example, a battery’s array configuration could be either 'series' or 'parallel'. As another example, a remote sensing resolution mode might be 'polar', 'track', or 'footprint'.

A string is written in single quotes '...'. Double quotes are not used for strings.

String Operators

There is no concatenation or mutation. Strings can only be compared for equality:

  • == - equal
  • != - not equal

String Examples

# battery.on
Battery configuration: config = 'series'

oneil eval battery.on \
  -x "config == 'series'" \
  -x "config == 'array'"

config == 'series' = true
config == 'array' = false

Booleans

Boolean literals are the keywords true and false.

Boolean Operators

  • not - logical NOT (unary)
  • and - logical AND
  • or - logical OR

Boolean Examples

Comparisons on numbers (and string equality) also yield booleans. Booleans are used in piecewise parameter conditions and in test declarations; those topics appear in later chapters.