Calc

A dumb/simple embeddable language for performing simple calculations It's so simple that you know it won't throw errors or run forever.

    ($area / 0.96) x 1.05 in 0.96kg
    $area x 0.05 
    (2 x $centreline_length) x (2 x $width)

The first part of a Calc program is an expression, which can contain numbers or variables with basic mathematical operators.

Variables are a word with a $ at the start e.g. $width

The operators are + for addition, - for subtraction, x for multiplication and / for division. Expressions may also be surrounded by parentheses e.g. (4 + 5) * 6.

Optionally, a Calc program may end with quantities prefaced by the in keyword. A quantity is a number, a unit, or a number followed by a unit e.g. 56, kg or 56kg.

A unit is any number of letters, optionally followed by a number. e.g. kg, L, m3

If a quantity contains a number the result will be expressed in whole multiples of that number, e.g. 4.5 in 1.5 -> 3 x 1.5

If there are multiple quantities, the result will be split among them e.g. 4.5 in 1.5, 3 -> 1 x 1.5, 1 x 3

Calc.render(src, variables) -> [{ value: Number, units: String? }, ...]

Render the Calc program src with the variables in variables, returns an array of { value: Number, unit: String or null }.

Calc.vars(src) -> [ String, ... ]

Returns a list of the variables that the Calc program src requires to be defined.

Calc.parse(src) -> Tree

Returns the parse tree for the Calc program src, for debuggery or meta-whatever.

A BNF grammar for Calc:

calc   := exp 'in' qtys | exp
qtys   := qty ',' qtys | qty  
qty    := number unit | unit
expr   := term '+' term | term '-' term | term
term   := factor 'x' term | factor '/' term | factor
factor := number | reference | '(' expr ')'