From e5a2e91c4243745aeedba4408c067a734d327d19 Mon Sep 17 00:00:00 2001
From: Lassi Kortela <lassi@lassi.io>
Date: Thu, 1 Dec 2022 20:40:16 +0200
Subject: [PATCH] Initial commit

---
 code/symbols-as-strings.sld |  86 +++++++++++++++++++++++++
 document.md                 | 123 ++++++++++++++++++++++++++++++++++++
 2 files changed, 209 insertions(+)
 create mode 100644 code/symbols-as-strings.sld
 create mode 100644 document.md

diff --git a/code/symbols-as-strings.sld b/code/symbols-as-strings.sld
new file mode 100644
index 0000000..1668507
--- /dev/null
+++ b/code/symbols-as-strings.sld
@@ -0,0 +1,86 @@
+(define-library (symbols-as-strings)
+  (export symbol-length
+          symbol<?
+          symbol-ci<?
+          symbol-prefix?
+          symbol-suffix?
+          symbol-middle
+          symbol-substring
+          symbol-append
+          symbol-transform)
+  (import (scheme base)
+          (scheme case-lambda))
+  (cond-expand ((library (srfi 13))
+                (import (only (srfi 13)
+                              string-prefix?
+                              string-suffix?)))
+               ((library (srfi 130))
+                (import (only (srfi 130)
+                              string-prefix?
+                              string-suffix?))))
+  (begin
+
+    (define (symbol-length symbol)
+      (string-length (symbol->string symbol)))
+
+    (define (symbol<? symbol1 symbol2)
+      (string<? (symbol->string symbol1)
+                (symbol->string symbol2)))
+
+    (define (symbol-ci<? symbol1 symbol2)
+      (string-ci<? (symbol->string symbol1)
+                   (symbol->string symbol2)))
+
+    (define (symbol-prefix? prefix symbol)
+      (string-prefix? prefix symbol))
+
+    (define (symbol-suffix? suffix symbol)
+      (string-suffix? suffix symbol))
+
+    (define symbol-middle
+      (case-lambda
+       ((symbol prefix)
+        (symbol-middle symbol prefix ""))
+       ((symbol prefix suffix)
+        (let ((suffix (or suffix ""))
+              (str (symbol->string symbol)))
+          (and (string-prefix? prefix str)
+               (string-suffix? suffix str)
+               (substring str
+                          (string-length prefix)
+                          (- (string-length str)
+                             (string-length suffix))))))))
+
+    (define symbol-substring
+      (case-lambda
+       ((symbol start)
+        (let ((str (symbol->string symbol)))
+          (substring str start (string-length str))))
+       ((symbol start end)
+        (let ((str (symbol->string symbol)))
+          (substring str start (or end (string-length str)))))))
+
+    (define (symbol-append . parts)
+      (string->symbol
+       (apply string-append
+              (map (lambda (part)
+                     (cond ((string? part)
+                            part)
+                           ((char? part)
+                            (string part))
+                           ((symbol? part)
+                            (symbol->string part))
+                           ((and (integer? part)
+                                 (exact? part)
+                                 (not (negative? part)))
+                            (number->string part))
+                           ((not part)
+                            "")
+                           (else
+                            (error "Bad symbol part" part))))
+                   parts))))
+
+    (define (symbol-transform string-proc symbol . args)
+      (string->symbol (apply string-proc
+                             (symbol->string symbol)
+                             args)))))
diff --git a/document.md b/document.md
new file mode 100644
index 0000000..1d3fbee
--- /dev/null
+++ b/document.md
@@ -0,0 +1,123 @@
+# SR 2022-2: Symbols as strings
+
+## Author
+
+Lassi Kortela
+
+## Status
+
+Draft
+
+## Abstract
+
+Each Scheme symbol corresponds to a string. This covenience library
+lets the programmer manipulate the string representations of symbols
+simply by passing the symbols, omitting the step of converting back
+and forth between symbols and strings.
+
+## Review
+
+This library is patterned after the following prior art.
+
+* R7RS
+* SRFI 13 (String Libraries)
+* SRFI 115 (Scheme Regular Expressions)
+
+RnRS provides:
+
+* `symbol?`
+* `symbol=?`
+* `symbol->string`
+* `string->symbol`
+
+## Specification
+
+`(symbol-length symbol) -> integer`
+
+Returns the *string-length* of _symbol_ as a string.
+
+`(symbol<? symbol1 symbol2) -> boolean`
+
+Returns the result of *string<?* applied to the symbols as strings.
+
+`(symbol-ci<? symbol1 symbol2) -> boolean`
+
+Returns the result of *string-ci<?* applied to the symbols as strings.
+
+`(symbol-prefix? prefix-string symbol) -> boolean`
+
+`(symbol-suffix? suffix-string symbol) -> boolean`
+
+Returns `#t` if _symbol_ as a string starts with _prefix-string_ or
+ends with _suffix-string_, respectively. Else returns `#f`.
+
+Matching is case sensitive. A zero-length string matches any symbol.
+
+[Modeled after SRFI 13 *string-prefix?* and *string-suffix?*.]
+
+`(symbol-middle symbol prefix-string [suffix-string]) -> string`
+
+If _symbol_ as a string starts with _prefix-string_ and ends with
+_suffix-string_, returns the part between them as a string. Else
+returns `#f`.
+
+Matching is done as with *symbol-prefix?* and *symbol-suffix?*. If
+_suffix-string_ is omitted or `#f`, a zero-length string is assumed.
+
+`(symbol-substring symbol start [end]) -> string`
+
+Returns the part of _symbol_ as a string between the character indexes
+_start_ (inclusive) and _end_ (exclusive). If _end_ is omitted of
+`#f`, it defaults to the length of the string.
+
+Mutating the result string does not change the symbol.
+
+`(symbol-append object ...) -> symbol`
+
+Like *string-append* from RnRS, but the result is a symbol instead of
+a string, and each _object_ can be any of:
+
+* a string
+* a character (converted as if by *string*)
+* a symbol (converted as if by *symbol->string*)
+* a non-negative exact integer (converted as if by *number->string*)
+* `#f` (ignored as if it were a zero-length string)
+
+`(symbol-transform string-proc symbol arg ...) -> symbol`
+
+Return `(string->symbol (string-proc (symbol->string symbol) arg ...))`
+
+## Examples
+
+### Comparing symbols
+
+```
+(list-sort symbol<? (features))
+```
+
+### Extracting parts of symbols
+
+```
+(symbol-substring 'geronimo 2 6)  ; => "roni"
+
+(symbol-middle 'make-move! "" "")  ; => "make-move!"
+(symbol-middle 'make-move! "" "!")  ; => make-move
+(symbol-middle 'make-move! "make-" "!")  ; => "move"
+(symbol-middle 'make-move! "make+" "!")  ; => #f
+```
+
+### Making new symbols
+
+```
+(symbol-append)      ; => ||
+(symbol-append #\a)  ; => a
+(symbol-append "a")  ; => a
+
+(symbol-append 'foo ":")  => |foo:|
+
+(let ((count 99) (things "bottles") (ask? #f))
+  (symbol-append "start-with-" count #\- things
+                 (and ask? #\?)))   ; => start-with-99-bottles
+
+(symbol-transform string-upcase 'yeah)  ; => YEAH
+```