10 REM A DEF call takes its environment from the pool, one per call, exactly as
20 REM GOSUB does. It used to be owned by the funcdef and reset on every call,
30 REM which cost two silent defects: two calls in one expression shared a slot,
40 REM and recursion never came back at all.
50 DEF FACT(N#)
60 IF N# <= 1 THEN RETURN 1
70 RETURN N# * FACT(N# - 1)
80 PRINT FACT(5)
90 REM Each frame keeps its own argument, which is what makes the unwind work.
100 DEF SUMTO(N#)
110 IF N# <= 0 THEN RETURN 0
120 RETURN N# + SUMTO(N# - 1)
130 PRINT SUMTO(4)
140 REM And two calls to one function in one expression no longer collide.
150 DEF DBL(N#) = N# * 2
160 PRINT DBL(10) + DBL(1)
170 PRINT DBL(1) + DBL(10) + DBL(100)
180 REM Depth answers to the environment pool now, so runaway recursion reports
190 REM "Environment pool exhausted" rather than hanging. It is not exercised here
200 REM because the statement containing a failed call still prints a junk value
210 REM afterwards -- a separate, pre-existing defect recorded in TODO.md, and one
220 REM this golden file would pin if it went in. tests/user_functions.c asserts
230 REM the message instead.