Update instructions to apply to Guile

Also rename `main` to `main.lua` and `main.scm` to `main`.

4 files changed, 73 insertions, 67 deletions

diff --git a/README.md b/README.md
index e2c5cc5..0c29b03 100644
--- a/README.md
+++ b/README.md
@@ -1,16 +1,22 @@
 # Advent of code 2024
 
-These are my solutions for Advent of Code in 2024.  This year I'm using Lua as the programming language.  To launch the program for a given day, run
+These are my solutions for Advent of Code in 2024.  This year I'm using Guile
+Scheme as the programming language.  To launch the program for a given day, run
 
 ```sh
 ./main <<ID>> [<<FILE>>]
 ```
 
-where `<<ID>>` is the day number followed by `a` for the first part or `b` for the second part.  If the file is not specified, it defaults to the number of the day with two digits and extension `.in`, i.e. `01.in`.  One can use the name of a file that doesn't exist, e.g. `-`, to read from standard input.
+where `<<ID>>` is the day number followed by `a` for the first part or `b` for
+the second part.  If the file is not specified, it defaults to the number of the
+day with two digits and extension `.in`, i.e. `01.in`.  To read from standard
+input, use `-` as the file name.
 
 Example:
 
 ```sh
-./main 01b input
+./main 05b -
 ```
 
+Some of the first days are written in Lua rather than Guile Scheme.  To run
+them, simply replace `main` with `main.lua`.
diff --git a/main b/main
index 38189ee..39f8da9 100755
--- a/main
+++ b/main
@@ -1,29 +1,35 @@
-#!/usr/bin/lua
-
-if #arg < 1 or #arg > 2 then
-    error ("Syntax: %s <DAY><a|b> [inputfile]"):format(arg[0])
-    os.exit(1)
-end
-
-local num, letter = arg[1]:match("^(%d+)([ab])$")
-if not num then
-    error ('Expected <DAY><a|b> as first argument (e.g. "01b"), got: %s'):format(arg[1])
-    os.exit(1)
-end
-num = tonumber(num)
-
-local script = ("%02d.lua"):format(num)
-local infile = arg[2] or ("%02d.in"):format(num)
-local input_stream = io.open(infile)
-if input_stream then
-    io.input(input_stream)
-else
-    print "Reading from standard input."
-end
-
-local parsed = loadfile(script)()
-if letter == 'a' then
-    parsed:part1()
-else
-    parsed:part2()
-end
+#!/usr/bin/env guile
+!#
+
+(use-modules (ice-9 format) (ice-9 regex))
+
+(define args (program-arguments))
+
+(unless (<= 2 (length args) 3)
+  (error (format #f "Syntax: ~a <DAY><a|b> [INFILE]\n" (car args)))
+  (exit 1))
+
+(define mtch (string-match "^([0-9]+)(a|b)$" (list-ref args 1)))
+
+(unless mtch
+  (error (format #f "Expected day and part (like \"03a\" or \"02b\"), got: ~a"
+                 (list-ref args 1))))
+
+(define day (format #f "~2,'0d" (string->number (match:substring mtch 1))))
+(define part (if (string= (match:substring mtch 2) "a") 'part1 'part2))
+
+(set! %load-path (cons "." %load-path))
+
+(define day-module
+  (resolve-module (list (string->symbol (string-append "day" day)))))
+(define func (module-ref day-module part))
+
+(define input-file
+  (cond ((= (length args) 2) (string-append day ".in"))
+        ((string= (list-ref args 2) "-") #f)
+        (else (list-ref args 2))))
+
+(display (if input-file
+             (call-with-input-file input-file func)
+             (func (current-input-port))))
+(newline)
diff --git a/main.lua b/main.lua
new file mode 100755
index 0000000..38189ee
--- /dev/null
+++ b/main.lua
@@ -0,0 +1,29 @@
+#!/usr/bin/lua
+
+if #arg < 1 or #arg > 2 then
+    error ("Syntax: %s <DAY><a|b> [inputfile]"):format(arg[0])
+    os.exit(1)
+end
+
+local num, letter = arg[1]:match("^(%d+)([ab])$")
+if not num then
+    error ('Expected <DAY><a|b> as first argument (e.g. "01b"), got: %s'):format(arg[1])
+    os.exit(1)
+end
+num = tonumber(num)
+
+local script = ("%02d.lua"):format(num)
+local infile = arg[2] or ("%02d.in"):format(num)
+local input_stream = io.open(infile)
+if input_stream then
+    io.input(input_stream)
+else
+    print "Reading from standard input."
+end
+
+local parsed = loadfile(script)()
+if letter == 'a' then
+    parsed:part1()
+else
+    parsed:part2()
+end
diff --git a/main.scm b/main.scm
deleted file mode 100755
index 39f8da9..0000000
--- a/main.scm
+++ /dev/null
@@ -1,35 +0,0 @@
-#!/usr/bin/env guile
-!#
-
-(use-modules (ice-9 format) (ice-9 regex))
-
-(define args (program-arguments))
-
-(unless (<= 2 (length args) 3)
-  (error (format #f "Syntax: ~a <DAY><a|b> [INFILE]\n" (car args)))
-  (exit 1))
-
-(define mtch (string-match "^([0-9]+)(a|b)$" (list-ref args 1)))
-
-(unless mtch
-  (error (format #f "Expected day and part (like \"03a\" or \"02b\"), got: ~a"
-                 (list-ref args 1))))
-
-(define day (format #f "~2,'0d" (string->number (match:substring mtch 1))))
-(define part (if (string= (match:substring mtch 2) "a") 'part1 'part2))
-
-(set! %load-path (cons "." %load-path))
-
-(define day-module
-  (resolve-module (list (string->symbol (string-append "day" day)))))
-(define func (module-ref day-module part))
-
-(define input-file
-  (cond ((= (length args) 2) (string-append day ".in"))
-        ((string= (list-ref args 2) "-") #f)
-        (else (list-ref args 2))))
-
-(display (if input-file
-             (call-with-input-file input-file func)
-             (func (current-input-port))))
-(newline)