M operates with a single basic data type, string. However, M evaluates data using methods that vary according to context.
When M syntax specifies a numexpr, M evaluates the data as a sequence of ASCII characters that specify a number. M stops the evaluation and provides the result generated from successfully evaluated characters when it encounters any character that is not the following:
A digit 0-9
A plus sign (+) or minus sign (-) and also the first character in the string
The first decimal point (.) in the string
GT.M provides 18 digits of accuracy, independent of the decimal point (.) placement, and a numeric range from 10**(-43) to (10**47). Numbers with three digits or fewer to the right of the decimal point are precise.
When M syntax specifies an intexpr, M evaluates the data as it would a numexpr except that it stops the evaluation at any decimal point including the first.
When M syntax specifies a tvexpr, M evaluates the data as a numeric. However, it stops the evaluation and returns a true value (1) as soon as it encounters a non-zero digit, otherwise it returns a false value (0). In other words, M treats expressions that have a non-zero numeric value as true, and expressions that have a zero numeric value as false. The sign and/or decimal have no affect on the evaluation of a truth-valued expression.
