OCaml backend: render case ranges compactly for char type.

OCaml supports character ranges like 'a'..'z', but it does not support
numeric ranges like 0..9, therefore previously all ranges were rendered
in expanded form, like 'a'|'b'|'c'|...|'z'. This results in sometimes
very long lines with a lot of alternatives in match expressions.

This commit fixes it by adding a conditional into syntax file
definition. It checks if the range is of char type. If so, then the
range is rendered compactly.

bootstrap/src/default_syntax_ocaml.cc

@@ -148,9 +148,14 @@ const char* DEFAULT_SYNTAX_OCAML =
     "    [case{0:-2}: topindent \"| \" case nl]\n"
     "    [case{-1}:   topindent \"| \" case \" -> \" [stmt: stmt] nl];\n"
     "\n"
-    "// Note: we cannot use `\"c when \" [val{0}: val] \" <= c && c <= \" [val{-1}: val]`, as it causes\n"
-    "// `Error: Variable c must occur on both sides of this | pattern` when there are multiple cases.\n"
-    "code:switch_case_range = [val{0}: val] [val{1:-1}: \"|\" val];\n"
+    "// In OCaml only literals of type `char` support case ranges.\n"
+    "// For `int`, we have to exlicitly list all range values. We cannot use\n"
+    "//     `\"c when \" [val{0}: val] \" <= c && c <= \" [val{-1}: val]`\n"
+    "// as it causes error when there are multiple cases:\n"
+    "//     `Error: Variable c must occur on both sides of this | pattern`.\n"
+    "code:switch_case_range = (char_literals\n"
+    "    ? [val{0}: val] (multival ? \"..\" [val{-1}: val])\n"
+    "    : [val{0}: val] [val{1:-1}: \"|\" val]);\n"
     "\n"
     "code:switch_case_default = \"_\";\n"
     "\n"