Analysis of information sources in references of the Wikipedia article "Principle of least astonishment" in English language version.
PL/I is infamous in this regard, as it converts nearly any type into any other type, sometimes with surprising results. Consider the expression 1/3 + 25. In PL/I this expression has the value 5.33333333333. Why? One-third is computed to 15 digits of precision, 14 to the right of the decimal point. Then 25 is coerced to the same precision, losing the most significant digit 2! This does raise an error in PL/I, but the default is to ignore it. This first appeared in print in Barron 1968, where it is given as a violation of a folk law of language design: 'the law of least astonishment.'
As a friend of mine once remarked to me—this must have been sometime in the late 1960s—whatever else you might say about it, there's one thing that PL/I is most definitely not, and that's 'the language of least astonishment.'
Could there be a high astonishment factor associated with the new feature? If a feature is accidentally misapplied by the user and causes what appears to him to be an unpredictable result, that feature has a high astonishment factor and is therefore undesirable. If a necessary feature has a high astonishment factor, it may be necessary to redesign the feature.
unfortunately, the expression '25 + 1/3' yields 5.33333333333333
Lest the non-PL/I programmer come to the erroneous conclusion that PL/I is without flaws, consider the following examples of PL/I's hostility. The rules for type conversion in PL/I are enough to give programmers ulcers. What other language would produce a fatal error when evaluating the expression (25 + 1/3)? (Just as bad, if you suppress the error checking, the result of evaluating the expression is 5.3333...)
Consider the following expression: 25+1/3. The result of evaluating this expression is undefined and the FIXEDOVERFLOW condition is raised because FIXED division results in a value of maximum implementation defined precision. [...] The results of the two evaluations are reached as shown in Table 29.
If the input string begins with "0" (a zero), radix is assumed to be 8 (octal) or 10 (decimal). Exactly which radix is chosen is implementation-dependent. ECMAScript 5 clarifies that 10 (decimal) should be used, but not all browsers support this yet.
Could there be a high astonishment factor associated with the new feature? If a feature is accidentally misapplied by the user and causes what appears to him to be an unpredictable result, that feature has a high astonishment factor and is therefore undesirable. If a necessary feature has a high astonishment factor, it may be necessary to redesign the feature.
unfortunately, the expression '25 + 1/3' yields 5.33333333333333
