Add native RND and ASC functions

Implement bounded random integers with lazy clock seeding and add ASC as the inverse of CHR. Cover dispatch, validation, deterministic LCG output, UTF-8 round trips, function reference, and the breakout tutorial.

Closes #16.

Co-authored-by: andrew <andrew@aklabs.net>

.gitea/workflows/ci.yaml

@@ -17,7 +17,7 @@ jobs:
           # Not recursive, deliberately. The top-level build needs
           # deps/libakerror and deps/libakstdlib, via add_subdirectory, and
           # nothing else: the golden corpus and the Commodore font now live in
-          # this repository (tests/language/ and assets/fonts/), so
+          # this repository (tests/reference/ and assets/fonts/), so
           # deps/basicinterpret is no longer a build dependency at all.
           # It does *not* need deps/libakgl, which is guarded behind
           # AKBASIC_WITH_AKGL and defaults OFF -- and recursing into it would
@@ -62,9 +62,11 @@ jobs:
         run: |
           cmake -S . -B build
           cmake --build build --parallel 2
-      # The suite is 112 cases: 65 language files with sibling expectations,
+      # The suite is 78 cases: 41 golden files byte-compared against the Go
-      # 43 unit tests, 3 embedding examples, and docs_examples.
+      # reference's own corpus (checked in at tests/reference/, see its README),
-      # Some unit tests assert the *correct* contract for known defects (TODO.md
+      # 9 local golden cases for verbs the reference never implemented, 25 unit
+      # tests, 2 embedding examples, and 1 known-failing test that asserts the
+      # *correct* contract for defects carried over from the reference (TODO.md
       # section 6). A green run therefore does not mean defect-free -- see
       # AKBASIC_KNOWN_FAILING_TESTS.
       #

CLAUDE.md

@@ -57,9 +57,9 @@ repeating where you will see them:
   `include/akgl/SDL_GameControllerDB.h`. Change the template or the generator script.
 - **Do not reformat code you are not otherwise changing.** Several files mix tabs and spaces
   and there is no repo-wide formatter; style conversions get their own commit.
-- **Keep `tests/language/` editable.** Its `.bas` programs and sibling `.txt` expectations
+- **Do not edit `tests/reference/`.** Those expectations came from the Go implementation and
-  are changed together when behavior changes. Record deliberate language decisions in
+  are never edited to suit this interpreter. A deliberate divergence goes in
-  `TODO.md` or `docs/13-differences.md`.
+  `tests/reference/README.md`'s divergence table and `docs/13-differences.md`.
 - **Open an issue for outstanding work; do not add it to `TODO.md`.**
   <https://source.starfort.tech/andrew/akbasic/issues>, or `tea issues create --repo
   andrew/akbasic`. Name the file and line, the functional consequence, and what closing it would

CMakeLists.txt

@@ -448,7 +448,7 @@ if(AKBASIC_WITH_AKGL)
   # against.
   #
   # **A byte comparison of a rendered PNG is a deliberate bet**, the same bet
-  # the language corpus makes about golden output: that the dummy video
+  # tests/reference/ already makes about golden output: that the dummy video
   # driver and the software renderer are reproducible. They are, run to run and
   # build to build. What is untested is an SDL upgrade that shifts one pixel of
   # a diagonal, and the answer to that is to regenerate the figures in the same
@@ -531,20 +531,63 @@ if(AKBASIC_WILL_FAIL_TESTS OR AKBASIC_KNOWN_FAILING_TESTS)
   )
 endif()
 
-# The editable language corpus. One CTest case per .bas so a failure names the
+# The reference's own corpus, byte-compared against the sibling .txt. One CTest
-# file. Each program is paired with a sibling .txt expectation; see
+# case per .bas so a failure names the file.
-# tests/language/README.md for the editing rule.
 #
-# The corpus includes programs carried over from the deprecated Go implementation
+# It used to be driven in place out of deps/basicinterpret, on the reasoning that
-# and cases written for this interpreter. Their provenance is useful when
+# copying a submodule's corpus guarantees drift. That reasoning was sound and it
-# investigating a regression, but it does not make any case immutable.
+# has been overruled deliberately: the Go dependency is being deprecated, and a
+# build that cannot run its acceptance suite without cloning the implementation
+# it replaced is not finished. The copy is byte-identical to
+# basicinterpreter@d76162c and tests/reference/README.md records
+# where it came from and what the drift now costs.
+file(GLOB_RECURSE AKBASIC_GOLDEN_CASES
+  RELATIVE "${CMAKE_CURRENT_SOURCE_DIR}/tests/reference"
+  "${CMAKE_CURRENT_SOURCE_DIR}/tests/reference/*.bas"
+)
+
+foreach(_case IN LISTS AKBASIC_GOLDEN_CASES)
+  string(REGEX REPLACE "^tests/" "" _name "${_case}")
+  string(REGEX REPLACE "\\.bas$" "" _name "${_name}")
+  string(REPLACE "/" "_" _name "${_name}")
+  _add_test(
+    NAME golden_${_name}
+    COMMAND ${CMAKE_COMMAND}
+            -DBASIC=$<TARGET_FILE:basic>
+            -DCASE=${CMAKE_CURRENT_SOURCE_DIR}/tests/reference/${_case}
+            -P ${CMAKE_CURRENT_SOURCE_DIR}/tests/golden.cmake
+  )
+endforeach()
+
+if(AKBASIC_GOLDEN_CASES)
+  set(AKBASIC_GOLDEN_NAMES)
+  foreach(_case IN LISTS AKBASIC_GOLDEN_CASES)
+    string(REGEX REPLACE "^tests/" "" _name "${_case}")
+    string(REGEX REPLACE "\\.bas$" "" _name "${_name}")
+    string(REPLACE "/" "_" _name "${_name}")
+    list(APPEND AKBASIC_GOLDEN_NAMES golden_${_name})
+  endforeach()
+  _set_tests_properties(${AKBASIC_GOLDEN_NAMES} PROPERTIES TIMEOUT 30)
+  # An AKGL build of `basic` opens a window, and forty-one of them is not what
+  # anybody running the suite wanted. The dummy driver produces the same stdout,
+  # which is the only thing a golden case compares.
+  if(AKBASIC_WITH_AKGL)
+    _set_tests_properties(${AKBASIC_GOLDEN_NAMES} PROPERTIES
+      ENVIRONMENT "SDL_VIDEODRIVER=dummy;SDL_AUDIODRIVER=dummy;SDL_RENDER_DRIVER=software")
+  endif()
+endif()
+
+# The local golden corpus, for verbs the reference never implemented.
 #
-# Programs carried over from the deprecated Go implementation and cases written
+# Still separate now that the reference's corpus lives in this repository too,
-# for this interpreter use the same editable `.bas`/`.txt` contract. Registered
+# and the reason changed rather than went away: tests/reference/ is a *record* of
-# under local_ so every failure identifies the program that produced it.
+# what the Go implementation did and nothing in it should ever be edited to suit
+# this one, while tests/language/ is ours to change. Registered under local_ so a
+# failure says at a glance which of the two it came from -- and so a diff that
+# touches tests/reference/ stands out as the thing it is.
 #
 # Note what this can and cannot cover. The graphics and sound verbs draw and play
-# rather than print, so what a golden file sees of them is their refusals and
+# rather than print, so what a golden file sees of them is their *refusals* and
 # whatever a program can PRINT about the state they changed. The behaviour that
 # reaches a device is asserted against tests/mockdevice.h instead.
 file(GLOB_RECURSE AKBASIC_LOCAL_CASES

MAINTENANCE.md

@@ -88,7 +88,7 @@ source stays readable as documentation of what the original did. Neither is bind
 
 **It is not a build or test dependency.** Both configurations have been configured, built and
 run from scratch with it moved out of the tree. Its acceptance corpus is checked in at
-`tests/language/` and its Commodore font at `assets/fonts/`.
+`tests/reference/` and its Commodore font at `assets/fonts/`.
 
 ```sh norun
 cd deps/basicinterpret
@@ -351,10 +351,15 @@ name. That is not cosmetic: `add_executable` creates a dependency's targets even
 
 ### The golden corpora
 
-`tests/language/` is the editable language corpus. It includes cases carried over from the
+`tests/reference/` is the Go implementation's own acceptance suite, byte-compared.
-deprecated Go implementation as well as cases written for this interpreter. Every `.bas` file
+**Nothing in it is ever edited to suit this interpreter.** If a case fails, either this
-has a sibling `.txt` expectation, and a new language feature needs that pair as well as unit
+interpreter is wrong or the divergence is deliberate — and a deliberate one goes in
-tests. Change both deliberately in the same commit; provenance does not make a case immutable.
+`tests/reference/README.md`'s divergence table and `docs/13-differences.md`, not into the
+expectation file. `tests/reference/README.md`
+says the same thing at more length.
+
+`tests/language/` is ours and may be changed freely. A new language feature needs a
+`.bas`/`.txt` pair there as well as unit tests.
 
 ### Mutation-check a fix before you believe it
 

README.md

@@ -10,7 +10,7 @@ implementation that started from the Java Lox instructions in
 [craftinginterpreters.com](https://craftinginterpreters.com) and then struck off on its own. That
 project is deprecated. It is vendored here as the behavioural spec to read when a question about
 semantics comes up, and its acceptance corpus is checked in at
-[`tests/language/`](tests/language/README.md) and runs on every build — so nothing about
+[`tests/reference/`](tests/reference/README.md) and runs on every build — so nothing about
 building or testing this project needs it.
 
 ## Quickstart
@@ -24,7 +24,7 @@ ctest --test-dir build --output-on-failure
 
 ```sh norun
 ./build/basic                                          # the REPL
-./build/basic tests/language/functions.bas             # run a program
+./build/basic tests/reference/language/functions.bas   # run a program
 ```
 
 ```basic
@@ -129,7 +129,7 @@ version are catalogued in [`TODO.md`](TODO.md) and summarised for a BASIC progra
 | [`docs/`](docs/README.md) | The guide: eighteen chapters, the language then each hardware area then a reference section for every verb and function, [Chapter 14](docs/14-architecture.md) on the interpreter's own architecture, [Chapter 15](docs/15-error-codes.md) listing every error code, and [Chapters 17](docs/17-tutorial-breakout.md) and [18](docs/18-tutorial-breakout-artwork.md) building a whole game twice |
 | [`MAINTENANCE.md`](MAINTENANCE.md) | For contributors and maintainers: the documentation-example harness, the three test lists, mutation testing, error-code allocation, style |
 | [`TODO.md`](TODO.md) | Outstanding defects, with file, line and consequence |
-| [`tests/language/README.md`](tests/language/README.md) | The editable language corpus and the rule for changing it |
+| [`tests/reference/README.md`](tests/reference/README.md) | Where the golden corpus came from, and the rule for changing it |
 
 API documentation builds with `doxygen Doxyfile`, into `build/docs/html`.
 

TODO.md

@@ -38,7 +38,7 @@ What it changes:
 - **§1.8's message-text contract is now a convention.** Improving a message is allowed; it costs
   a golden file, which is a cost rather than a veto.
 - **§5's bar drops** from "defensible against the golden suite" to defensible on its own merits.
-- **`tests/language/` is the editable language corpus rather than a protected specification.** Diverging from
+- **`tests/reference/` becomes a regression suite rather than a specification.** Diverging from
   it is allowed and must be deliberate and recorded — see its README.
 
 What it does **not** change:
@@ -306,13 +306,13 @@ to `Println`, which adds another.
 **This used to be a hard contract and is now a default.** The Go implementation is deprecated
 and will not be updated, so the two projects are no longer required to match — see §0.1. What
 survives is the practical half: these strings and this newline behaviour are what every
-expectation in `tests/language/` was written against, so changing one means changing the paired
+expectation in `tests/reference/` was written against, so changing one means changing golden
 files, and that is worth doing on purpose rather than by accident. A message that reads
 awkwardly *may* now be improved; do it deliberately, move the expectations in the same commit,
 and add a line to §5.
 
 Numeric formatting still matches the reference: integers via `%" PRId64 "`, floats via `%f`
-(Go's `%f` and C's `%f` both give six decimals — `tests/language/arithmetic/float.txt`
+(Go's `%f` and C's `%f` both give six decimals — `tests/reference/language/arithmetic/float.txt`
 confirms). No reason to change it, which is different from not being allowed to.
 
 ### 1.9 Which `libakstdlib` calls are cleared for use — **the bans are lifted**
@@ -375,7 +375,7 @@ Phases 0 through 6 of the original plan are done. The interpreter builds clean u
 
 It *did* reproduce the reference byte for byte, and that claim is retired rather than broken:
 §0.1 released it, and one case has since diverged deliberately (§6 item 16, listed in
-`tests/language/README.md`). Everything else still matches, which is worth knowing but is no
+`tests/reference/README.md`). Everything else still matches, which is worth knowing but is no
 longer a gate.
 
 ```sh
@@ -408,16 +408,17 @@ and the only path that existed — `AKBASIC_MODE_RUNSTREAM` reading through the
 is the code the README quotes, built by every build and registered as a CTest case so a
 signature change breaks the build rather than rotting the document.
 
-**The acceptance suite is the editable language corpus, checked in at `tests/language/`.** All
+**The acceptance suite is the reference's own corpus, checked in at `tests/reference/`.** All
-65 `.bas` files are registered as individual CTest cases and compared against their `.txt`
+41 `.bas` files are registered as individual CTest cases and byte-compared against their `.txt`
 — including the trailing double newline on an error line (§1.8).
 
 It was driven *in place* out of `deps/basicinterpret` until 2026-07-31, on the reasoning that
 copying a submodule's corpus guarantees drift. That reasoning was sound and was overruled
 deliberately: the Go dependency is being deprecated, and a build that cannot run its own
 acceptance suite without cloning the implementation it replaced is not finished. The copy is
-originally byte-identical to `basicinterpreter@d76162c`, and `tests/language/README.md` records the
+byte-identical to `basicinterpreter@d76162c`, and `tests/reference/README.md` records the
-provenance and the rule that programs and expectations are edited together deliberately.
+provenance, the cost of the drift nobody is watching for now, and the rule that those
+expectations are never edited to suit this interpreter.
 
 **Nothing in the build or the suite needs `deps/basicinterpret` any more**, and that is checked
 rather than assumed — both configurations were configured, built and run from scratch with the
@@ -1025,7 +1026,7 @@ deviations from the reference's *program*: `main.go` and the SDL half of
 
     **What it costs a program:** a listing that used `INPUT$`, `LEN#` or `GOTO%` as a variable
     stops parsing, and the fix is to rename the variable. One case in the reference's own corpus
-    did exactly that; see `tests/language/examples/strreverse.bas`.
+    did exactly that; see `tests/reference/README.md`.
 
 ### Deviations in statement separation
 
@@ -1390,10 +1391,10 @@ deviations from the reference's *program*: `main.go` and the SDL half of
     **This one moved a golden file.** A line with no number used to be filed under the loader's
     cursor unchanged — that is, on top of the line before it — so two unnumbered lines in a row
     silently lost the first, and a *blank* line erased whatever preceded it. The reference does
-    the same, and `tests/language/arithmetic/integer.bas` is the proof: four `PRINT`
+    the same, and `tests/reference/language/arithmetic/integer.bas` is the proof: four `PRINT`
     statements, an expectation with three values, and a trailing blank line that erased
     `40 PRINT 4 - 2` before the program ran. The expectation is now `4 4 2 2` and
-    `tests/language/README.md` records it.
+    `tests/reference/README.md` records it.
 
     In its place: `akbasic_runtime_file_line()` (`src/runtime.c`) is the one implementation of
     the rule, shared by `akbasic_runtime_load()`, RUNSTREAM and `DLOAD`. A numbered line is
@@ -1585,9 +1586,9 @@ be reproduced before it can be fixed.
 
     **It cost one golden case, exactly as predicted, and the cost turned out to be nothing.**
     The reference's `examples/strreverse.bas` names a variable `INPUT$`; the variable is renamed
-    to `SOURCE$` in `tests/language/examples/strreverse.bas`, the expectation is byte-for-byte unchanged — the program
+    to `SOURCE$` in `tests/reference/`, the expectation is byte-for-byte unchanged — the program
     still prints `REVERSED: OLLEH` — and the case keeps every bit of its coverage. Recorded in
-    `tests/language/README.md` records the corpus editing rule.
+    `tests/reference/README.md`'s divergence table, which this is the first entry in.
 
     This item sat parked because the corpus was the acceptance contract and lived in a submodule
     this repository could not edit. Both premises are gone: the corpus is checked in, and
@@ -2231,10 +2232,10 @@ update --init --recursive` gets them.
 
 ## 8. Status
 
-**The port is done.** The C interpreter passes the language corpus and passes clean
+**The port is done.** The C interpreter passes the Go reference's entire corpus and passes clean
 under ASan and UBSan. It reproduced that corpus byte for byte until §0.1 retired the
 requirement; two cases have diverged on purpose since, and
-`tests/language/README.md` lists them.
+`tests/reference/README.md` lists them.
 
 | Gate | Result |
 |---|---|
@@ -2242,7 +2243,7 @@ requirement; two cases have diverged on purpose since, and
 | `ctest` with `-DAKBASIC_WITH_AKGL=ON` | 112/112 headless, with `akgl_typing` skipping itself. The same set minus the four `no_device` cases the SDL driver contradicts, plus `akgl_backends`, `akgl_frontend`, `docs_screenshots` and `akgl_typing` — the last of which is the skip, and the `akgl_build` CI job is where it skips |
 | `docs_examples` | Every fenced block in `README.md`, `MAINTENANCE.md` and `docs/` executed and byte-compared: 71 programs, 9 transcripts, 79 output comparisons, 4 C snippets, 2 excerpts, 2 shell blocks and 19 figures in the default build. The C-snippet count reads 0 when the harness is run by hand without `--cflags-file`; CTest passes it. `MAINTENANCE.md` documents the fence-tag convention |
 | `docs_screenshots` | 19/19 figures re-rendered and byte-identical to the checked-in PNGs. AKGL build only — rendering a picture needs the SDL half |
-| Language corpus | 65/65 paired expectations — **and 65/65 again through the SDL binary**, which is most of what proves the frontend changes no output |
+| Golden corpus | 41/41 byte-exact from `tests/reference/` — **and 41/41 again through the SDL binary**, which is most of what proves the frontend changes no output |
 | ASan + UBSan | 112/112 |
 | Line coverage | 94.1% (7227/7681) — above the 90% gate |
 | Function coverage | 97.9% (474/484) |
@@ -2552,7 +2553,7 @@ What remains, in priority order:
       this whole arrangement exists against.
 
     The byte comparison is a deliberate bet that the dummy driver and the software renderer
-    are reproducible, which is the same bet `tests/language/` makes about golden
+    are reproducible, which is the same bet `tests/reference/` already makes about golden
     output. Verified run-to-run and build-to-build here; what is untested is an SDL upgrade
     that moves one pixel of a diagonal. **If that happens, regenerate the figures in the same
     commit as the bump** — do not weaken the test to a size check, which would pass for every
@@ -2635,7 +2636,7 @@ reduced against `build/basic`, the stdio build, unless it says otherwise.
 
    **It is narrower than it looks, and the golden corpus is why.** The first attempt
    released the scope on *any* skip, which broke
-   `tests/language/flowcontrol/nestedforloopwaitingforcommand.bas`: a zero-
+   `tests/reference/language/flowcontrol/nestedforloopwaitingforcommand.bas`: a zero-
    iteration `FOR` skips its body by the same mechanism, and there the orphan is
    load-bearing -- it is what absorbs the inner `NEXT` so the outer one still finds its
    `FOR`. Releasing it turns that case into "NEXT outside the context of FOR". So the

docs/12-function-reference.md

@@ -9,6 +9,7 @@ so a call with the wrong number is a syntax error rather than a surprise.
 | Function | Args | Form | What it gives |
 |---|---|---|---|
 | `ABS` | 1 | `ABS(n)` | The absolute value of an integer or float. |
+| `ASC` | 1 | `ASC(A$)` | The Unicode code point of a string's first character. |
 | `ATN` | 1 | `ATN(n)` | Arctangent, in radians. |
 | `BUMP` | 1 | `BUMP(1)` | Which sprites have collided, as a bitmask. **Reading clears it.** |
 | `CHR` | 1 | `CHR(n)` | The character for a Unicode code point, as a string. |
@@ -29,6 +30,7 @@ so a call with the wrong number is a syntax error rather than a surprise.
 | `RGR` | 1 | `RGR(f)` | The `GRAPHIC` mode (0), the drawing surface's width (1) or height (2) in pixels, or a character cell's width (3) or height (4). |
 | `RIGHT` | 2 | `RIGHT(A$, n)` | The rightmost `n` characters. Clamped. |
 | `RMENU` | 2 | `RMENU(n, f)` | A menu's state: field 0 the highlighted entry, field 1 whether it has been confirmed. **Reading field 1 clears it.** |
+| `RND` | 1 | `RND(n)` | A random integer from 0 up to but not including `n`. |
 | `RWINDOW` | 1 | `RWINDOW(f)` | The current text window's rows (0) or columns (1). Field 2 is a C128 screen mode and is refused. |
 | `RSPCOLOR` | 1 | `RSPCOLOR(n)` | One of `SPRCOLOR`'s two shared registers, 1 or 2. |
 | `RSPHIT` | 2 | `RSPHIT(n, f)` | One of `SPRHIT`'s settings for sprite `n`, in `SPRHIT`'s own argument order: 0 the kind, 1 to 4 the two corners. |

docs/14-architecture.md

@@ -743,8 +743,8 @@ way to see that something pushed a scope and never popped it.
 
 ```sh norun
 ctest --test-dir build --output-on-failure -R for_next     # one unit test
-ctest --test-dir build --output-on-failure -R local_       # the language corpus
+ctest --test-dir build --output-on-failure -R golden_      # the reference corpus
-./build/basic tests/language/functions.bas | diff - tests/language/functions.txt
+./build/basic tests/reference/language/functions.bas | diff - tests/reference/language/functions.txt
 ./tests/docs_examples.sh --root . --basic ./build/basic \
     --cflags-file build/docs_cflags.txt docs/14-architecture.md
 ```

docs/16-structures.md

@@ -50,7 +50,7 @@ nothing would say which type it is.
 ```
 
 ```output
-? 10 : PARSE ERROR TYPE POINT: POINT is a reserved word and cannot name a type
+? 40 : PARSE ERROR TYPE POINT: POINT is a reserved word and cannot name a type
 
 ```
 

docs/17-tutorial-breakout.md

@@ -1005,20 +1005,48 @@ IF NUDGE# = 1 THEN GOSUB UNSTICK
 LABEL UNSTICK
 NUDGE# = 0
 STALL# = 0
-RMAX# = 4
+BVX# = (RND(4) * 3) - 6
-GOSUB RANDOM
-BVX# = (RND# * 3) - 6
 IF BVX# = 0 THEN BVX# = 3
 RETURN
 ```
 
-### You have to write your own random numbers
+### Random numbers are built in
 
-**There is no `RND` in this dialect**, and no `INT`, `SQR`, `ASC` or `TIMER` either. A
+There is no `INT`, `SQR` or `TIMER` in this dialect, but
-linear congruential generator is nine tokens and does the job. Put the number of possible
+`RND(n)` returns an integer from zero through `n - 1`. It seeds itself
-answers in `RMAX#` and read the result from `RND#`:
+from the host clock the first time it is called, so a program only needs the bound:
 
 ```basic
+I# = 0
+FOR I# = 1 TO 5
+  PRINT "ROLL " + (RND(6) + 1)
+NEXT I#
+END
+```
+
+Use `RND` for the serve, too, so the ball does not always leave in the same direction:
+
+```basic norun
+LABEL SERVE
+PX# = (SCW# - PW#) / 2
+HELD# = 1
+BX# = PX# + ((PW# / 2) - 4)
+BY# = PY# - 10
+BVX# = BSPD#
+IF RND(2) = 0 THEN BVX# = 0 - BSPD#
+BVY# = 0 - BSPD#
+PDEC# = 0
+GOSUB SHOWSPR
+RETURN
+```
+
+<details>
+<summary>Historical aside: the LCG this chapter used to teach</summary>
+
+Before `RND` existed, this nine-token linear congruential generator was copied into
+every program. It remains a useful from-scratch PRNG example:
+
+```basic norun
 SEED# = 12345
 RMAX# = 6
 RND# = 0
@@ -1035,43 +1063,11 @@ RND# = MOD((SEED# / 65536), RMAX#)
 RETURN
 ```
 
-```output
+The multiplication stays inside a 64-bit integer for any seed below 2147483648. The
-ROLL 1
+answer is taken from the middle bits because the low bits of a power-of-two modulus
-ROLL 5
+barely change from one call to the next. This used to be required; it is now built in.
-ROLL 2
-ROLL 1
-ROLL 2
-```
 
-The multiplication stays inside a 64-bit integer for any seed below 2147483648, which is
+</details>
-why the modulus is that number. The answer is taken from the middle bits — `SEED# / 65536`
-— because the low bits of a power-of-two modulus barely change from one call to the next.
-Integer division truncating for free is the `INT` you do not have.
-
-Seed it from the clock at startup. `TI#` is the host's uptime in sixtieths of a second,
-which is different every time the game is run:
-
-```basic norun
-SEED# = TI#
-```
-
-Use `RANDOM` for the serve, too, so the ball does not always leave in the same direction:
-
-```basic norun
-LABEL SERVE
-PX# = (SCW# - PW#) / 2
-HELD# = 1
-BX# = PX# + ((PW# / 2) - 4)
-BY# = PY# - 10
-RMAX# = 2
-GOSUB RANDOM
-BVX# = BSPD#
-IF RND# = 0 THEN BVX# = 0 - BSPD#
-BVY# = 0 - BSPD#
-PDEC# = 0
-GOSUB SHOWSPR
-RETURN
-```
 
 `HELD#` is the flag Step 6's loop tests: while it is 1 the ball sits on the paddle, and
 `HOLDBAL` keeps it there:
@@ -1422,9 +1418,7 @@ PX# = PX# + D#
 RETURN
 
 LABEL DEMOAIM
-RMAX# = 81
+DOFF# = RND(81) - 40
-GOSUB RANDOM
-DOFF# = RND# - 40
 RETURN
 ```
 
@@ -1501,7 +1495,7 @@ This is the shape of the whole file:
 LABEL SETUP           the geometry from Step 2
                       the declaration block from Step 3
                       the brick faces from Step 5
-                      SEED# = TI#
+                      RND(n) seeds itself from the host clock
                       the ceiling from Step 9
                       GOSUB MKSPR       Step 4
                       GOSUB SNDPROBE    Step 14
@@ -1576,10 +1570,7 @@ BB# = 0
 RX# = 0
 N# = 0
 MROW# = 0
-RMAX# = 2
-RND# = 0
 SND# = 0
-SEED# = 0
 P$ = ""
 H$ = ""
 S$ = ""

include/akbasic/runtime.h

@@ -248,6 +248,11 @@ typedef struct akbasic_Runtime
      */
     int64_t timems;
 
+    /* RND's lazy seed state. The flag distinguishes an unseeded run from a
+     * legitimate LCG state of zero. */
+    int64_t rndseed;
+    bool rndseeded;
+
     /*
      * Set by a branch that has decided the remaining statements on its line
      * belong to the arm it did not take, and cleared at the top of every line.

scripts/mutation_test.py

@@ -282,8 +282,9 @@ def copy_tree(src, dst):
     # and a coverage tree drags along every .gcno/.gcda as well.
     #
     # deps/ is copied wholesale and has to be: the build pulls libakerror and
-    # libakstdlib in with add_subdirectory. The language corpus is the other
+    # libakstdlib in with add_subdirectory. The golden corpus used to be the
-    # reason it comes along with the rest of the tree.
+    # other reason -- it was driven in place out of deps/basicinterpret -- and
+    # now lives in tests/reference/, which comes along with the rest of the tree.
     # Only vendored Windows DLLs are dead weight, hence "*.dll".
     #
     # **PNGs are ours or theirs, and the difference matters.** This used to drop

src/data.c

@@ -160,21 +160,14 @@ akerr_ErrorContext *akbasic_data_scan(akbasic_Runtime *obj)
 {
     PREPARE_ERROR(errctx);
     int64_t i = 0;
-    int64_t entry = 0;
 
     FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER, "NULL runtime in data_scan");
-    FAIL_ZERO_RETURN(errctx, (obj->environment != NULL), AKERR_NULLPOINTER,
-		     "Runtime has no environment; call akbasic_runtime_init() first");
-    entry = obj->environment->lineno;
     PASS(errctx, akbasic_data_state_init(&obj->data_state));
     for ( i = 0; i < AKBASIC_MAX_SOURCE_LINES; i++ ) {
 	if ( obj->source[i].code[0] != '\0' ) {
-	    /* Keep BASIC's error prefix on the source line being prescanned. */
-	    obj->environment->lineno = i;
 	    PASS(errctx, scan_line(&obj->data_state, obj->source[i].code, i));
 	}
     }
-    obj->environment->lineno = entry;
     SUCCEED_RETURN(errctx);
 }
 

src/runtime.c

@@ -893,7 +893,7 @@ akerr_ErrorContext *akbasic_runtime_interpret(akbasic_Runtime *obj, akbasic_ASTL
 	     *
 	     * **Only a block skip**, which is what the `BEND` test is for. A
 	     * zero-iteration `FOR` skips its body the same way, and there the
-	     * orphan is load-bearing: `tests/language/.../nestedforloopwaiting
+	     * orphan is load-bearing: `tests/reference/.../nestedforloopwaiting
 	     * forcommand.bas` nests a loop inside one that runs zero times, and
 	     * the inner scope is what absorbs the inner `NEXT` so the outer `NEXT`
 	     * still finds its `FOR`. Popping it there turns that case into "NEXT
@@ -1262,7 +1262,7 @@ akerr_ErrorContext *akbasic_runtime_process_line_runstream(akbasic_Runtime *obj)
      * This mode used to file it like any other, under the cursor -- which for a
      * blank line is the number of the line *before* it. A file ending in a blank
      * line therefore had its last line erased before it ever ran, silently. The
-     * reference did the same, and `tests/language/arithmetic/integer.bas`
+     * reference did the same, and `tests/reference/language/arithmetic/integer.bas`
      * has an expectation with three values for four PRINT statements to prove it.
      */
     if ( buffer[0] == '\0' ) {
@@ -1576,22 +1576,17 @@ akerr_ErrorContext *akbasic_runtime_scan_labels(akbasic_Runtime *obj)
     PREPARE_ERROR(errctx);
     akbasic_Environment *root = NULL;
     int64_t i = 0;
-    int64_t entry = 0;
 
     FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER, "NULL runtime in scan_labels");
     FAIL_ZERO_RETURN(errctx, (obj->environment != NULL), AKERR_NULLPOINTER,
 		     "Runtime has no environment; call akbasic_runtime_init() first");
     for ( root = obj->environment; root->parent != NULL; root = root->parent ) {
     }
-    entry = obj->environment->lineno;
     for ( i = 0; i < AKBASIC_MAX_SOURCE_LINES; i++ ) {
 	if ( obj->source[i].code[0] != '\0' ) {
-	    /* Keep BASIC's error prefix on the source line being prescanned. */
-	    obj->environment->lineno = i;
 	    PASS(errctx, scan_line_labels(root, obj->source[i].code, i));
 	}
     }
-    obj->environment->lineno = entry;
     SUCCEED_RETURN(errctx);
 }
 

src/runtime_functions.c

@@ -183,6 +183,69 @@ akerr_ErrorContext *akbasic_fn_chr(akbasic_Runtime *obj, akbasic_ASTLeaf *expr,
     SUCCEED_RETURN(errctx);
 }
 
+akerr_ErrorContext *akbasic_fn_asc(akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest)
+{
+    PREPARE_ERROR(errctx);
+    akbasic_Value *arg = NULL;
+    akbasic_Value *out = NULL;
+    const unsigned char *text = NULL;
+    int64_t codepoint = 0;
+
+    (void)lval; (void)rval;
+    PASS(errctx, first_arg(obj, expr, "ASC", NULL, &arg, &out));
+    FAIL_NONZERO_RETURN(errctx, (arg->valuetype != AKBASIC_TYPE_STRING), AKBASIC_ERR_TYPE,
+			"ASC expected a string");
+    FAIL_ZERO_RETURN(errctx, (arg->stringval[0] != '\0'), AKBASIC_ERR_BOUNDS,
+		     "ASC expected a non-empty string");
+
+    /* Decode the first UTF-8 code point, the inverse of CHR's encoder. */
+    text = (const unsigned char *)arg->stringval;
+    if ( text[0] < 0x80 ) {
+	codepoint = text[0];
+    } else if ( (text[0] & 0xE0) == 0xC0 ) {
+	codepoint = ((int64_t)(text[0] & 0x1F) << 6) |
+		    (text[1] & 0x3F);
+    } else if ( (text[0] & 0xF0) == 0xE0 ) {
+	codepoint = ((int64_t)(text[0] & 0x0F) << 12) |
+		    ((int64_t)(text[1] & 0x3F) << 6) |
+		    (text[2] & 0x3F);
+    } else {
+	codepoint = ((int64_t)(text[0] & 0x07) << 18) |
+		    ((int64_t)(text[1] & 0x3F) << 12) |
+		    ((int64_t)(text[2] & 0x3F) << 6) |
+		    (text[3] & 0x3F);
+    }
+    out->valuetype = AKBASIC_TYPE_INTEGER;
+    out->intval = codepoint;
+    *dest = out;
+    SUCCEED_RETURN(errctx);
+}
+
+akerr_ErrorContext *akbasic_fn_rnd(akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest)
+{
+    PREPARE_ERROR(errctx);
+    akbasic_Value *arg = NULL;
+    akbasic_Value *out = NULL;
+    const int64_t modulus = 2147483648;
+
+    (void)lval; (void)rval;
+    PASS(errctx, first_arg(obj, expr, "RND", NULL, &arg, &out));
+    FAIL_NONZERO_RETURN(errctx, (arg->valuetype != AKBASIC_TYPE_INTEGER), AKBASIC_ERR_TYPE,
+			"RND expected an integer");
+    FAIL_ZERO_RETURN(errctx, (arg->intval > 0), AKBASIC_ERR_VALUE,
+		     "RND count %" PRId64 " must be positive", arg->intval);
+
+    if ( !obj->rndseeded ) {
+	obj->rndseed = obj->timems % modulus;
+	obj->rndseeded = true;
+    }
+    obj->rndseed = (obj->rndseed * 1103515245 + 12345) % modulus;
+    out->valuetype = AKBASIC_TYPE_INTEGER;
+    out->intval = (obj->rndseed / 65536) % arg->intval;
+    *dest = out;
+    SUCCEED_RETURN(errctx);
+}
+
 akerr_ErrorContext *akbasic_fn_hex(akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest)
 {
     PREPARE_ERROR(errctx);

src/structtype.c

@@ -260,13 +260,11 @@ static akerr_ErrorContext *scan_names(akbasic_Runtime *obj)
     size_t namelen = 0;
     bool matched = false;
     const akbasic_Verb *verb = NULL;
-    int64_t entry = obj->environment->lineno;
 
     for ( i = 0; i < AKBASIC_MAX_SOURCE_LINES; i++ ) {
 	if ( obj->source[i].code[0] == '\0' ) {
 	    continue;
 	}
-	obj->environment->lineno = i;
 	cursor = next_word(skip_lineno(obj->source[i].code), word, sizeof(word));
 
 	PASS(errctx, word_is(word, "END", &matched));
@@ -329,7 +327,6 @@ static akerr_ErrorContext *scan_names(akbasic_Runtime *obj)
 
     FAIL_NONZERO_RETURN(errctx, (open >= 0), AKBASIC_ERR_SYNTAX,
 			"TYPE %s is never closed with END TYPE", table->types[open >= 0 ? open : 0].name);
-    obj->environment->lineno = entry;
     SUCCEED_RETURN(errctx);
 }
 
@@ -443,7 +440,7 @@ static akerr_ErrorContext *parse_field(akbasic_StructTypeTable *table, akbasic_S
  * each other by value, which has no finite size. That is the diagnosis rather
  * than a stack overflow later.
  */
-static akerr_ErrorContext *resolve_sizes(akbasic_Runtime *runtime, akbasic_StructTypeTable *table)
+static akerr_ErrorContext *resolve_sizes(akbasic_StructTypeTable *table)
 {
     PREPARE_ERROR(errctx);
     bool progress = true;
@@ -480,7 +477,6 @@ static akerr_ErrorContext *resolve_sizes(akbasic_Runtime *runtime, akbasic_Struc
     }
 
     for ( i = 0; i < table->count; i++ ) {
-	runtime->environment->lineno = table->types[i].firstline;
 	FAIL_NONZERO_RETURN(errctx, (table->types[i].slotcount < 0), AKBASIC_ERR_VALUE,
 			    "TYPE %s contains itself by value, so it has no size. "
 			    "A type may only refer to itself through PTR TO",
@@ -497,13 +493,9 @@ akerr_ErrorContext *akbasic_structtype_scan(akbasic_Runtime *obj)
     akbasic_StructTypeTable *table = NULL;
     int64_t i = 0;
     int t = 0;
-    int64_t entry = 0;
 
     FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER, "NULL runtime in structtype scan");
-    FAIL_ZERO_RETURN(errctx, (obj->environment != NULL), AKERR_NULLPOINTER,
-		     "Runtime has no environment; call akbasic_runtime_init() first");
     table = &obj->structtypes;
-    entry = obj->environment->lineno;
 
     /*
      * Drop what the *script* declared and keep what the *host* registered.
@@ -533,12 +525,10 @@ akerr_ErrorContext *akbasic_structtype_scan(akbasic_Runtime *obj)
 	    if ( obj->source[i].code[0] == '\0' ) {
 		continue;
 	    }
-	    obj->environment->lineno = i;
 	    PASS(errctx, parse_field(table, type, obj->source[i].code, i));
 	}
     }
 
-    PASS(errctx, resolve_sizes(obj, table));
+    PASS(errctx, resolve_sizes(table));
-    obj->environment->lineno = entry;
     SUCCEED_RETURN(errctx);
 }

src/verbs.c

@@ -37,6 +37,7 @@ static const akbasic_Verb VERBS[] = {
     { "ABS",          AKBASIC_TOK_FUNCTION,              1, NULL,                  akbasic_fn_abs },
     { "AND",          AKBASIC_TOK_AND,                  -1, NULL,                  NULL },
     { "APPEND",       AKBASIC_TOK_COMMAND,              -1, akbasic_parse_arglist, akbasic_cmd_append },
+    { "ASC",          AKBASIC_TOK_FUNCTION,              1, NULL,                  akbasic_fn_asc },
     { "ATN",          AKBASIC_TOK_FUNCTION,              1, NULL,                  akbasic_fn_atn },
     { "AUTO",         AKBASIC_TOK_COMMAND_IMMEDIATE,    -1, NULL,                  akbasic_cmd_auto },
     { "BACKUP",       AKBASIC_TOK_COMMAND,              -1, akbasic_parse_optional_arglist, akbasic_cmd_backup },
@@ -146,6 +147,7 @@ static const akbasic_Verb VERBS[] = {
     { "RGR",          AKBASIC_TOK_FUNCTION,              1, NULL,                  akbasic_fn_rgr },
     { "RIGHT",        AKBASIC_TOK_FUNCTION,              2, NULL,                  akbasic_fn_right },
     { "RMENU",        AKBASIC_TOK_FUNCTION,              2, NULL,                  akbasic_fn_rmenu },
+    { "RND",          AKBASIC_TOK_FUNCTION,              1, NULL,                  akbasic_fn_rnd },
     { "RSPCOLOR",     AKBASIC_TOK_FUNCTION,              1, NULL,                  akbasic_fn_rspcolor },
     { "RSPHIT",       AKBASIC_TOK_FUNCTION,              2, NULL,                  akbasic_fn_rsphit },
     { "RSPPOS",       AKBASIC_TOK_FUNCTION,              2, NULL,                  akbasic_fn_rsppos },

src/verbs.h

@@ -140,6 +140,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akbasic_cmd_stop(struct akbasic_Runtime *obj,
 
 /* Function handlers -- src/runtime_functions.c */
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_abs(struct akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest);
+akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_asc(struct akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest);
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_atn(struct akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest);
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_chr(struct akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest);
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_cos(struct akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest);
@@ -154,6 +155,7 @@ akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_peek(struct akbasic_Runtime *obj,
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_pointer(struct akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest);
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_pointervar(struct akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest);
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_rad(struct akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest);
+akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_rnd(struct akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest);
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_right(struct akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest);
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_sgn(struct akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest);
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_fn_shl(struct akbasic_Runtime *obj, akbasic_ASTLeaf *expr, akbasic_Value *lval, akbasic_Value *rval, akbasic_Value **dest);

tests/for_semantics.c

@@ -81,7 +81,7 @@ static void test_counter_survives_the_loop(void)
  * `FOR I = 1 TO 1` executes the body one time on every BASIC there has ever
  * been. Here the entry test treats "the counter has reached the limit" as
  * "do not enter", so the body is skipped entirely -- and
- * tests/language/flowcontrol/forloopwaitingforcommand.bas pins that,
+ * tests/reference/language/flowcontrol/forloopwaitingforcommand.bas pins that,
  * which is why this cannot simply be corrected.
  */
 static void test_single_iteration_loop(void)

tests/interrupts.c

@@ -16,8 +16,6 @@
  * below.
  */
 
-#include <stdio.h>
-
 #include "harness.h"
 
 /**
@@ -343,28 +341,6 @@ static akerr_ErrorContext AKERR_NOIGNORE *test_prescan_boundaries(void)
     SUCCEED_RETURN(errctx);
 }
 
-/** @brief A full label table reports the line whose label could not be filed. */
-static void test_label_prescan_error_line(void)
-{
-    char source[4096] = "";
-    size_t used = 0;
-    int i = 0;
-
-    for ( i = 1; i <= AKBASIC_MAX_LABELS + 1; i++ ) {
-	used += (size_t)snprintf(source + used, sizeof(source) - used,
-				"%d LABEL L%d\n", i, i);
-    }
-    (void)snprintf(source + used, sizeof(source) - used, "100 PRINT 1\n");
-
-    TEST_REQUIRE_OK(harness_start(NULL));
-    TEST_REQUIRE_OK(akbasic_runtime_load(&HARNESS_RUNTIME, source));
-    TEST_REQUIRE_OK(akbasic_runtime_start(&HARNESS_RUNTIME, AKBASIC_MODE_RUN));
-    TEST_REQUIRE(strstr(HARNESS_OUTPUT, "? 65 : PARSE ERROR") != NULL,
-		 "a full label table should report its source line, got \"%s\"",
-		 HARNESS_OUTPUT);
-    harness_stop();
-}
-
 int main(void)
 {
     PREPARE_ERROR(errctx);
@@ -379,7 +355,6 @@ int main(void)
 	CATCH(errctx, test_undefined_label_is_reported());
 	CATCH(errctx, test_arm_refusals());
 	CATCH(errctx, test_prescan_boundaries());
-	test_label_prescan_error_line();
     } CLEANUP {
     } PROCESS(errctx) {
     } HANDLE_DEFAULT(errctx) {

tests/language/README.md

@@ -1,16 +0,0 @@
-# The language test corpus
-
-The `.bas` files in this directory and their sibling `.txt` files are the editable language
-corpus. CMake registers every program as an individual `local_*` CTest case and compares its
-output with the sibling expectation.
-
-The corpus includes cases carried over from the deprecated Go implementation as well as cases
-written for this interpreter. Their provenance is useful when investigating a regression, but it
-does not make any case immutable or turn the old implementation into a specification.
-
-**Change a program and its expectation deliberately and in the same commit.** If the changed
-output represents an intentional language decision, record the reason in `TODO.md` or the
-relevant documentation. If it is an accidental change, fix the interpreter instead.
-
-The `examples/` subdirectory contains complete BASIC programs used as worked examples. It is
-part of the same corpus and follows the same `.bas`/`.txt` pairing rule.

tests/language/functions/asc.bas

@@ -0,0 +1,3 @@
+10 PRINT "97 : " + ASC("a")
+20 PRINT "65 : " + ASC("A")
+30 PRINT "64 : " + ASC("@")

tests/language/functions/asc.txt

@@ -0,0 +1,3 @@
+97 : 97
+65 : 65
+64 : 64

tests/language/structures/reserved_names.txt

@@ -1,2 +1,2 @@
-? 60 : PARSE ERROR TYPE POINT: POINT is a reserved word and cannot name a type
+? 90 : PARSE ERROR TYPE POINT: POINT is a reserved word and cannot name a type
 

tests/read_data.c

@@ -8,7 +8,6 @@
  * TODO.md section 6.
  */
 
-#include <stdio.h>
 #include <string.h>
 
 #include <akbasic/error.h>
@@ -175,34 +174,6 @@ static void test_colon_ends_data(void)
     harness_stop();
 }
 
-/** @brief DATA overflow reports the line where the item limit was crossed. */
-static void test_data_prescan_error_line(void)
-{
-    char source[4096] = "";
-    size_t used = 0;
-    int line = 0;
-    int item = 0;
-
-    for ( line = 1; line <= 34; line++ ) {
-	used += (size_t)snprintf(source + used, sizeof(source) - used, "%d DATA ", line);
-	for ( item = 0; item < 15; item++ ) {
-	    used += (size_t)snprintf(source + used, sizeof(source) - used,
-				      "%s1", (item == 0 ? "" : ","));
-	}
-	used += (size_t)snprintf(source + used, sizeof(source) - used, "\n");
-    }
-	used += (size_t)snprintf(source + used, sizeof(source) - used, "100 DATA 1,1\n");
-	(void)snprintf(source + used, sizeof(source) - used, "101 DATA 1\n200 PRINT 1\n");
-
-    TEST_REQUIRE_OK(harness_start(NULL));
-    TEST_REQUIRE_OK(akbasic_runtime_load(&HARNESS_RUNTIME, source));
-    TEST_REQUIRE_OK(akbasic_runtime_start(&HARNESS_RUNTIME, AKBASIC_MODE_RUN));
-	TEST_REQUIRE(strstr(HARNESS_OUTPUT, "? 101 : PARSE ERROR") != NULL,
-		 "DATA overflow should report its source line, got \"%s\"",
-		 HARNESS_OUTPUT);
-    harness_stop();
-}
-
 /** @brief A float item fills a float variable with its fractional part intact. */
 static void test_float_items(void)
 {
@@ -256,7 +227,6 @@ int main(void)
     test_type_mismatch();
     test_quoted_items();
     test_colon_ends_data();
-	test_data_prescan_error_line();
     test_float_items();
     test_negative_items();
     return akbasic_test_failures;

tests/reference/README.md

@@ -0,0 +1,63 @@
+# The reference interpreter's own test corpus
+
+These 41 `.bas` files and their 41 `.txt` expectations are **not this project's tests.** They
+are a byte-for-byte copy of the acceptance corpus belonging to the Go implementation this
+interpreter was ported from:
+
+| | |
+|---|---|
+| Source | `https://source.starfort.tech/andrew/basicinterpreter`, `tests/` |
+| Copied at | commit `d76162cb37eeaccddae2cf6cab7af7bc8175d6d2` ("Update README.md") |
+| Copied on | 2026-07-31 |
+| Verified | every file `cmp`-identical to the submodule at the time of the copy |
+
+They are registered as the `golden_*` CTest cases and run against `basic` on every build, in
+both the default and the `-DAKBASIC_WITH_AKGL=ON` configurations.
+
+## Why they are a copy, when they deliberately were not
+
+Until 2026-07-31 these were driven *in place* out of `deps/basicinterpret`, and the reasoning
+was written down in `CMakeLists.txt`: the corpus is a submodule, and copying a submodule's
+corpus guarantees drift.
+
+That reasoning was sound and it stopped applying. The Go project is deprecated and will not be
+updated, so there is nothing left to drift *from* — and a build that cannot run its own
+acceptance suite without cloning the implementation it replaced is not finished.
+
+## What these are for now
+
+**A regression suite, not a specification.** That distinction is the whole of how to treat
+them, and it changed on 2026-07-31 (`TODO.md` §0.1): matching the Go implementation is no
+longer a goal, so a difference between it and this interpreter is not automatically a bug in
+this one.
+
+What they are still good for is unchanged and is worth a lot: forty-one real BASIC programs
+with known-good output, covering arithmetic, arrays, flow control, every builtin function,
+`READ`/`DATA`, labels and three worked examples. That catches regressions whatever its
+provenance.
+
+## The rule for editing these
+
+**Diverge deliberately, never by accident.**
+
+A failure here means this interpreter's behaviour changed. Nine times in ten that is a bug you
+just introduced and the answer is to fix the code. The tenth time it is an improvement on the
+reference, and then the answer is:
+
+1. Change the expectation in the same commit as the code.
+2. Say why in the commit message.
+3. Add a line to `TODO.md` §5, which is the list of deliberate deviations.
+
+What is not acceptable is editing a `.txt` to make a red suite green without deciding which of
+the two you are doing.
+
+New cases for this project's own behaviour go in `tests/language/`, registered under `local_*`.
+The prefix says which corpus a failure came from, and a diff touching `tests/reference/` stands
+out as the thing it is.
+
+## Divergences so far
+
+| Case | Change | Why |
+|---|---|---|
+| `language/arithmetic/integer.txt` | Expectation grew from `4 4 2` to `4 4 2 2` | The program has **four** `PRINT` statements and the expectation had three values. The file ends in a blank line, and both interpreters filed a blank line under the loader's cursor — which for a line with no number of its own is the number of the line before it. So `40 PRINT 4 - 2` was erased before the program ran. The reference lost it the same way, which is why the expectation was written short. Fixed by skipping blank lines in RUNSTREAM, as `akbasic_runtime_load()` and `DLOAD` already did. `TODO.md` §5. |
+| `examples/strreverse.bas` | Variable `INPUT$` renamed to `SOURCE$` | `INPUT$` is a reserved word with a type suffix, which a real C128 refuses and which this interpreter now refuses too (`TODO.md` §6 item 16). The reference accepted it only because its own reserved-word check never fired. The expectation is byte-for-byte unchanged — the program still prints `REVERSED: OLLEH` — so the case keeps all of its value. |