Targets & dialects

The two axes: target and dialect

They are orthogonal — any pairing is valid.

Target — the machine value model (integer word width + overflow, the logical-truth convention, the character codec):

• forterp.NATIVE — a clean 64-bit host: 64-bit two's-complement, 8-bit ASCII, .TRUE.=1 with boolean logicals. The default, for running standard F66 portably.
• forterp.PDP10 — the DEC FORTRAN-10 machine: 36-bit two's-complement, 5×7-bit packed ASCII, .TRUE.=−1 with bit-wise logicals. The faithful, validated opt-in.
• forterp.LP64LE — a 64-bit little-endian IEEE machine (32-bit INTEGER/REAL, 64-bit DOUBLE) — matches gfortran on x86_64; most useful with word_memory (below).
• forterp.VAX — a provisional, unvalidated 32-bit guess.
• forterp.Target(word_bits=…, chars_per_word=…, bits_per_char=…, logical_true=…, bitwise_logic=…, little_endian=…, truth=…, mem_model=…) — build your own.

forterp.run_source(src, target=forterp.PDP10)   # 36-bit arithmetic, packed ASCII

Faithful type punning — by default COMMON/EQUIVALENCE cells hold typed values, so reading the same storage as a different type isn't bit-faithful. Pass word_memory=True (PDP10/LP64LE/VAX only; CLI --word-memory) to store such blocks as raw machine words/bytes and reinterpret on access, so a REAL read as an INTEGER yields the genuine machine word — validated against a real KL10 (PDP10) and gfortran (LP64LE). Off by default: it changes the commons representation to raw words and costs ~2× per COMMON access. See the FORTRAN 66 manual, Appendix C.

forterp.run_source(src, target=forterp.PDP10, word_memory=True)  # bit-faithful punning

Dialect — the front-end language. forterp.F66 is strict ANSI X3.9-1966 and genuinely rejects non-F66 constructs; forterp.FORTRAN10 is the DEC superset (octal, tab-format, ! comments, apostrophe strings, random-access I/O, free-form input, the DEC intrinsic library); forterp.F77 is ANSI X3.9-1978 — the CHARACTER type, the block IF, list-directed and keyword-driven I/O, internal files, INQUIRE, PARAMETER/SAVE, and .EQV./.NEQV.. See the FORTRAN 77 reference manual for the language itself, and the F77 dialect knobs just below.

SourceOptions — orthogonal to the dialect; it copes with imperfect input, not a language variant. forterp.SourceOptions(recover_shifted_cols=True) keeps statement text that spilled past column 72 in a mechanically re-indented deck. The default is no recovery (columns 7–72, sequence field dropped).

The F77 dialect knobs

A Dialect is a set of front-end flags; forterp.F77 turns on exactly the subset ANSI X3.9-1978 standardized (several were split out of the broader DEC bundles so F77 gets the standardized feature without the rest of the DEC extension):

Knob	Enables
character_type	the CHARACTER data type — quoted strings become str, not Hollerith words
block_if	IF … THEN / ELSE IF / ELSE / END IF
list_directed_io	list-directed * READ/WRITE (split from the DEC extended_io bundle)
eqv_operators	.EQV. / .NEQV. (split from the DEC dec_operators bundle)
parameter_stmt	the PARAMETER statement
implicit_stmt	the IMPLICIT statement (incl. IMPLICIT CHARACTER*n)
save_stmt, intrinsic_stmt	SAVE / INTRINSIC
expr_subscripts	general integer expressions in subscripts and DO bounds
array_lower_bounds	DIMENSION A(lo:hi), assumed-size A(*), adjustable bounds
alt_return	alternate-return actual arguments (CALL S(*99))
mixed_complex_assign	COMPLEX ↔ numeric assignment
apostrophe_string	'…' string constants
f77_intrinsics	the ANSI F77 intrinsic additions (generic LOG/MAX/MIN, TAN/ASIN/…, the D… specifics, NINT/ANINT, LEN/CHAR/…)
dec_library	the DEC-only library: DEC intrinsics (LSH/ROT, degree trig, DOUBLE COMPLEX helpers) + DEC subprograms (RAN/DATE/…) + the DEC terminal CR-LF wrap
uuo_library	TOPS-10 monitor UUOs callable from FORTRAN (OUTSTR/SLEEP/GETTAB/…) — PDP-10-specific
strict_stmt_order	enforce "specifications before executables" (§3.5) as a hard error
carriage_control	off for F77 — standard output is a terminal, not a line printer

The strict/relax knobs recursion, unlimited_rank, and bounds_check are off by default on every dialect; see reference manual Appendix D.

Of the three library tiers, only f77_intrinsics is on for F77; dec_library and uuo_library are FORTRAN10-only, so strict F77 accepts neither LSH nor CALL SLEEP.

Notably off for F77 (on only for FORTRAN10): do_while, dec_operators (.XOR., ==/</>), slash_dim_bound (A(lo/hi)), octal_quote, tab_format, inline_comment (!), extended_io (TYPE/ACCEPT/ENCODE/DECODE, random-access), free_form_input, dec_library, uuo_library.