feat(library): add experimental string LCASE overloads

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

3 files changed, 25 insertions, 0 deletions

diff --git a/pseudocode-lib/README.md b/pseudocode-lib/README.md
index 55367d0..8049ede 100644
--- a/pseudocode-lib/README.md
+++ b/pseudocode-lib/README.md
@@ -24,3 +24,5 @@ The library provides `&`, `_EXP_STRING_NUM_TO_STR` (INTEGER/REAL), `_EXP_STRING_
 `_EXP_STRING_RIGHT(S : _EXP_STRING, Count : INTEGER)` returns a new `_EXP_STRING` containing up to Count bytes from the end. Nonpositive counts return an empty string; counts exceeding the length return the whole string. Embedded NUL bytes are preserved.
 
 `_EXP_STRING_MID(S : _EXP_STRING, Start : INTEGER, Count : INTEGER)` returns a new `_EXP_STRING` containing up to Count bytes from the one-based Start position. Starts below 1 clamp to 1; starts beyond the end and nonpositive counts return an empty string. Counts clamp to the remaining bytes. Embedded NUL bytes are preserved.
+
+`_EXP_STRING_LCASE(S : _EXP_STRING)` returns a new `_EXP_STRING` with letters converted to lower case. Its `(Ch : CHAR)` overload returns CHAR, following guide section 5.5. Nonletters and embedded NUL bytes are preserved; the source is unchanged. Use ASCII for predictable case conversion.
diff --git a/pseudocode-lib/_exp_string.cc b/pseudocode-lib/_exp_string.cc
index d406274..6155319 100644
--- a/pseudocode-lib/_exp_string.cc
+++ b/pseudocode-lib/_exp_string.cc
@@ -1,4 +1,5 @@
 #include <algorithm>
+#include <cctype>
 #include <cstdio>
 #include <exception>
 #include <stdexcept>
@@ -88,6 +89,18 @@ void _exp_string_impl_mid(void *Target, void *Handle, long long Start, long long
         text(Target) = Source.substr(Position, Length);
     });
 }
+void _exp_string_impl_lcase(void *Target, void *Handle) {
+    checked([&] {
+        text(Target) = text(Handle);
+        for (char &Ch : text(Target))
+            Ch = static_cast<char>(std::tolower(static_cast<unsigned char>(Ch)));
+    });
+}
+char _exp_string_impl_lcase_char(char Ch) {
+    return checked([&] {
+        return static_cast<char>(std::tolower(static_cast<unsigned char>(Ch)));
+    });
+}
 void _exp_string_impl_output(void *Handle) {
     checked([&] {
         const auto &Text = text(Handle);
diff --git a/pseudocode-lib/_exp_string.cps b/pseudocode-lib/_exp_string.cps
index 30eef71..a25b3ef 100644
--- a/pseudocode-lib/_exp_string.cps
+++ b/pseudocode-lib/_exp_string.cps
@@ -17,6 +17,8 @@ EXTERN "C" EXTERN_FUNCTION _exp_string_impl_length(_EXP_STRING_HANDLE) RETURNS _
 EXTERN "C" EXTERN_PROCEDURE _exp_string_impl_left(_EXP_STRING_HANDLE, _EXP_STRING_HANDLE, _EXP_STRING_C_INTEGER)
 EXTERN "C" EXTERN_PROCEDURE _exp_string_impl_right(_EXP_STRING_HANDLE, _EXP_STRING_HANDLE, _EXP_STRING_C_INTEGER)
 EXTERN "C" EXTERN_PROCEDURE _exp_string_impl_mid(_EXP_STRING_HANDLE, _EXP_STRING_HANDLE, _EXP_STRING_C_INTEGER, _EXP_STRING_C_INTEGER)
+EXTERN "C" EXTERN_PROCEDURE _exp_string_impl_lcase(_EXP_STRING_HANDLE, _EXP_STRING_HANDLE)
+EXTERN "C" EXTERN_FUNCTION _exp_string_impl_lcase_char(C_CHAR) RETURNS C_CHAR
 EXTERN "C" EXTERN_PROCEDURE _exp_string_impl_output(_EXP_STRING_HANDLE)
 
 CLASS _EXP_STRING
@@ -83,3 +85,11 @@ FUNCTION _EXP_STRING_MID(S : _EXP_STRING, Start : INTEGER, Count : INTEGER) RETU
     CALL _exp_string_impl_mid(Result._HANDLE, S._HANDLE, (_EXP_STRING_C_INTEGER)Start, (_EXP_STRING_C_INTEGER)Count)
     RETURN Result
 ENDFUNCTION
+OVERLOAD FUNCTION _EXP_STRING_LCASE(S : _EXP_STRING) RETURNS _EXP_STRING
+    DECLARE Result : _EXP_STRING
+    CALL _exp_string_impl_lcase(Result._HANDLE, S._HANDLE)
+    RETURN Result
+ENDFUNCTION
+OVERLOAD FUNCTION _EXP_STRING_LCASE(Ch : CHAR) RETURNS CHAR
+    RETURN (CHAR)_exp_string_impl_lcase_char((C_CHAR)Ch)
+ENDFUNCTION