Trigger words and prose safety

The most common worry about a calculator that reads prose is that it will start mangling the prose. This page explains why that mostly does not happen.

Words are not keywords

The engine needs total, average, tax, sum, line and many other ordinary words. If each were claimed as a keyword, a note containing “the total was disappointing” would start behaving strangely, and defining a variable named total would become impossible.

So they are not keywords. They are recognised only as part of a longer phrase, and only where that phrase forms a complete expression. average of 1, 2, 3 is recognised. A bare average is a name.

That is why this works:

:total = 100
:total + 5 // 105

Function-like names need the parenthesis

map, reduce, sum and prod are treated as operations only when immediately followed by an opening parenthesis. Otherwise they are ordinary names.

:sum = 42
:sum + 8 // 50

Labels are preserved

A line starting with a label keeps the label and evaluates the rest.

total: 5 + 3 // 8

When a line is not an expression

A line the engine cannot make sense of is left alone. It does not guess and it does not partially evaluate. That is the intended behaviour for a document that is mostly prose with occasional arithmetic in it.