feat(output)!: print REAL values in shortest round-trip form

OUTPUT and NUM_TO_STR now share Python repr formatting instead of %f.

BREAKING CHANGE: REAL output changes from six fixed decimals (2.500000) to the shortest round-trip text (2.5).

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

2 files changed, 23 insertions, 2 deletions

diff --git a/pseudocode-lib/README.md b/pseudocode-lib/README.md
index 1e360a4..4e70a44 100644
--- a/pseudocode-lib/README.md
+++ b/pseudocode-lib/README.md
@@ -34,7 +34,7 @@ The library provides `&`, six case-sensitive content comparisons, and these ordi
 - `LCASE(CHAR)` and `UCASE(CHAR)` return CHAR, following guide section 5.5. STRING overloads return independent strings. Nonletters and embedded NUL bytes are preserved; use ASCII for predictable case conversion.
 - `ASC(CHAR)` and `ASC(STRING)` return the unsigned character or first-byte code; an empty string returns zero.
 - `CHR(Code)` returns a one-byte STRING containing the low eight bits. `LENGTH(CHR(0))` is 1.
-- `NUM_TO_STR(INTEGER)` and `NUM_TO_STR(REAL)` use C++17 `std::to_string`, with six fractional digits for REAL.
+- `NUM_TO_STR(INTEGER)` and `NUM_TO_STR(REAL)` convert INTEGER to decimal text and REAL to the shortest round-trip text (Python `repr` style, identical to OUTPUT: `2.0`, `0.1`, `1e-07`, `inf`).
 - `STR_TO_NUM(S)` returns REAL through the same `parseNumber` helper as IS_NUM (`strtod`, full consumption). Invalid text and trailing junk throw `STR_TO_NUM: '<text>' is not a number`; overflow throws `... is out of the REAL range`; underflow is accepted.
 - `IS_NUM(S)` agrees with STR_TO_NUM: full consumption by `strtod` and no overflow, without throwing. Leading whitespace is accepted; trailing whitespace, trailing junk, empty input, embedded NUL bytes, and overflowing values (`1e999`) are rejected.
 
diff --git a/pseudocode-lib/string.cc b/pseudocode-lib/string.cc
index 34f1ec5..a4c7343 100644
--- a/pseudocode-lib/string.cc
+++ b/pseudocode-lib/string.cc
@@ -23,6 +23,27 @@ decltype(auto) checked(Operation &&Op) {
 }
 std::string &text(void *Handle) { return *static_cast<std::string *>(Handle); }
 
+// Python-repr-style shortest round-trip text for a REAL. Keep in sync with getOutputRealHelper in
+// lib/CodeGen/OutputGen.cc, which OUTPUT uses.
+std::string realText(double Number) {
+    if (std::isnan(Number)) return "nan";
+    if (std::isinf(Number)) return Number < 0 ? "-inf" : "inf";
+    char Buffer[64];
+    double Abs = std::fabs(Number);
+    if (Abs == 0 || (Abs >= 1e-4 && Abs < 1e16)) {
+        for (int Decimals = 1; Decimals < 40; ++Decimals) {
+            std::snprintf(Buffer, sizeof Buffer, "%.*f", Decimals, Number);
+            if (std::strtod(Buffer, nullptr) == Number) break;
+        }
+    } else {
+        for (int Precision = 0; Precision < 17; ++Precision) {
+            std::snprintf(Buffer, sizeof Buffer, "%.*e", Precision, Number);
+            if (std::strtod(Buffer, nullptr) == Number) break;
+        }
+    }
+    return Buffer;
+}
+
 enum class NumberStatus { Ok, Invalid, OutOfRange };
 
 // Shared by IS_NUM and STR_TO_NUM so that they always agree.
@@ -70,7 +91,7 @@ void _string_impl_from_int(void *Target, long long Number) {
     checked([&] { text(Target) = std::to_string(Number); });
 }
 void _string_impl_from_real(void *Target, double Number) {
-    checked([&] { text(Target) = std::to_string(Number); });
+    checked([&] { text(Target) = realText(Number); });
 }
 double _string_impl_to_real(void *Handle) {
     return checked([&] {