CLHS: Section 22.3.8.1

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## 22.3.8.1 Tilde Left-Paren: Case Conversion

`~(`str`~)`

The contained control string str is processed, and what it produces is subject to case conversion.

With no flags, every uppercase character is converted to the corresponding lowercase character.

`~:(` capitalizes all words, as if by string-capitalize.

`~@(` capitalizes just the first word and forces the rest to lower case.

`~:@(` converts every lowercase character to the corresponding uppercase character.

In this example `~@(` is used to cause the first word produced by `~@R` to be capitalized:

     (format nil "~@R ~(~@R~)" 14 14)
    =>  "XIV xiv"
     (defun f (n) (format nil "~@(~R~) error~:P detected." n)) =>  F
     (f 0) =>  "Zero errors detected."
     (f 1) =>  "One error detected."
     (f 23) =>  "Twenty-three errors detected."

When case conversions appear nested, the outer conversion dominates, as illustrated in the following example:

     (format nil "~@(how is ~:(BOB SMITH~)?~)")
     =>  "How is bob smith?"
     NOT=>  "How is Bob Smith?"

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