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diff --git a/chapter23/README.md b/chapter23/README.md index c99d2441..8f371e9b 100644 --- a/chapter23/README.md +++ b/chapter23/README.md @@ -3,7 +3,7 @@ English | [日本語](README.ja.md) [Previous: Chapter 22](../chapter22/README.md) | -[Next: Chapter 24](../chapter24/README.md) +[Next: Chapter 24a](../chapter24a/README.md) In this chapter we add *methods*, functions defined in structs which take a hidden `self` argument and can access the struct fields. Here is an @@ -53,6 +53,18 @@ You can also read [this chapter](https://github.com/SeaOfNodes/Simple/tree/linea Here is the [complete language grammar](docs/23-grammar.md) for this chapter. +## Chained comparisons + +`lo <= x < hi` compares adjacent values and evaluates `x` only once. If the +first comparison fails, the later operand is not evaluated. This uses the +same control and scope merges as short-circuit expressions; it does not need +SCCP. For example, `10 < 30 < 20` is false, and `0 < 2 <= 2` is true. + +A chain must keep one direction, but may mix strict and inclusive tests: +`a < b <= c` and `a >= b > c` are allowed; `a < b > c` is rejected. Equality +has lower precedence and does not join a chain. Parentheses can still make +the result of one comparison an operand of another. + ## Why Cyclic Types? Cyclic types give us a sharper analysis than the alternative, and thus admit |