-Time-stamp: <2004-11-30 22:59:24 blp>
+Time-stamp: <2005-03-02 16:08:59 blp>
What Ben's working on now.
--------------------------
Workspace exhaustion heuristics.
-Does SET work correctly?
-
Update q2c input format description.
Rewrite output subsystem, break into multiple processes.
Make valgrind --leak-check=yes --show-reachable=yes work.
-Add Boolean type.
-
Add NOT_REACHED() macro.
Add compression to casefiles.
-Expressions need to be able to abbreviate function names. XDATE.QUARTER
-abbreviates to XDA.QUA, etc.
-
-The expression tests need tests for XDATE and a few others, see
-tests/xforms/expressions.sh comments for details.
-
-Expressions need random distribution functions.
-
There needs to be another layer onto the lexer, which should probably be
entirely rewritten anyway. The lexer needs to read entire *commands* at a
time, not just a *line* at a time. It also needs to support arbitrary putback,
and results would be reported through HTML tables viewed with the user's choice
of web browsers. Help could be implemented through the browser as well.
-Design a plotting API, with scatterplots, line plots, pie charts, barcharts,
-Pareto plots, etc., as subclasses of the plot superclass.
-
HOWTOs
------
-1. How to add an operator for use in PSPP expressions:
-
-a. Add the operator to the enumerated type at the top of expr.h. If the
-operator has arguments (i.e., it's not a terminal) then add it *before*
-OP_TERMINAL; otherwise, add it *after* OP_TERMINAL. All these begin with OP_.
-
-b. If the operator's a terminal then you'll want to design a structure to hold
-its content. Add the structure to the union any_node. (You can also reuse one
-of the prefab structures, of course.)
-
-c. Now switch to expr-prs.c--the module for expression parsing. Insert the
-operator somewhere in the precedence hierarchy.
-
-(1) If you're adding a operator that is a function (like ACOS, ABS, etc.) then
-add the function to functab in `void init_functab(void)'. Order is not
-important here. The first element is the function name, like "ACOS". The
-second is the operator enumerator you added in expr.h, like OP_ARCOS. The
-third element is the C function to parse the PSPP function. The predefined
-functions will probably suit your needs, but if not, you can write your own.
-The fourth element is an argument to the parsing function; it's only used
-currently by generic_str_func(), which handles a rather general syntax for
-functions that return strings; see the comment at the beginning of its code for
-details.
-
-(2) If you're adding an actual operator you'll have to put a function in
-between two of the operators there already in functions `exprtype
-parse_*(any_node **n)'. Each of these stores the tree for its result into *n,
-and returns the result type, or EX_ERROR on error. Be sure to delete all the
-allocated memory on error before returning.
-
-d. Add the operator to the table `op_desc ops[OP_SENTINEL+1]' in expr-prs.c,
-which has an entry for every operator. These entries *must* be in the same
-order as they are in expr.h. The entries have the form `op(A,B,C,D)'. A is
-the name of the operator as it should be printed in a postfix output format.
-For example, the addition operator is printed as `plus'. B is a bitmapped set
-of flags:
-
-* Set the 001 bit (OP_VAR_ARGS) if the operator takes a variable number of
-arguments. If a function can take, say, two args or three args, but no other
-numbers of args, this is a poor way to do it--instead implement the operator as
-two separate operators, one with two args, the other with three. (The main
-effect of this bit is to cause the number of arguments to be output to the
-postfix form so that the expression evaluator can know how many args the
-operator takes. It also causes the expression optimizer to calculate the
-needed stack height differently, without referencing C.)
-
-* Set the 002 bit (OP_MIN_ARGS) if the operator can take an optional `dotted
-argument' that specified the minimum number of non-SYSMIS arguments in order to
-have a non-SYSMIS result. For instance, MIN.3(e1,e2,e3,e4,e5) returns a
-non-SYSMIS result only if at least 3 out of 5 of the expressions e1 to e5 are
-not missing.
-
-Minargs are passed in the nonterm_node structure in `arg[]''s elements past
-`n'--search expr-prs.c for the words `terrible crock' for an example of this.
-
-Minargs are output to the postfix form. A default value is output if none was
-specified by the user.
-
-You can use minargs for anything you want--they're not limited to actually
-describing a minimum number of valid arguments; that's just what they're most
-*commonly* used for.
-
-* Set the 004 bit (OP_FMT_SPEC) if the operator has an argument that is a
-format specifier. (This causes the format specifier to be output to the
-postfix representation.)
-
-Format specs are passed in the nonterm_node structure in the same way as
-minargs, except that there are three args, in this order: type, width, # of
-decimals--search expr-prs.c for the words `is a crock' for an example of this.
-
-* Set the 010 bit (OP_ABSORB_MISS) if the operator can *ever* have a result of
-other than SYSMIS when given one or more arguments of SYSMIS. Operators
-lacking this bit and known to have a SYSMIS argument are short-circuited to
-SYSMIS by the expression optimizer.
-
-* If your operator doesn't fit easily into the existing categories,
-congratulations, you get to write lots of code to adjust everything to cope
-with this new operator. Are you really sure you want to do that?
-
-C is the effect the operator has on stack height. Set this to `varies' if the
-operator has a variable number of arguments. Otherwise this 1, minus the
-number of arguments the operator has. (Since terminals have no arguments, they
-have a value of +1 for this; other operators have a value of 0 or less.)
-
-D is the number of items output to the postfix form after the operator proper.
-This is 0, plus 1 if the operator has varargs, plus 1 if the operator has
-minargs, plus 3 if the operator has a format spec. Note that minargs/varargs
-can't coexist with a format spec on the same operator as currently coded. Some
-terminals also have a nonzero value for this but don't fit into the above
-categories.
-
-e. Switch to expr-opt.c. Add code to evaluate_tree() to evaluate the
-expression when all arguments are known to be constants. Pseudo-random
-functions can't be evaluated even if their arguments are constants. If the
-function can be optimized even if its arguments aren't all known constants, add
-code to optimize_tree() to do it.
-
-f. Switch to expr-evl.c. Add code to evaluate_expression() to evaluate the
-expression. You must be absolutely certain that the code in evaluate_tree(),
-optimize_tree(), and evaluate_expression() will always return the same results,
-otherwise users will get inconsistent results, a Bad Thing. You must be
-certain that even on boundary conditions users will get identical results, for
-instance for the values 0, 1, -1, SYSMIS, or, for string functions, the null
-string, 1-char strings, and 255-char strings.
-
-g. Test the code. Write some test syntax files. Examine the output carefully.
-
MORE NOTES/IDEAS/BUGS
---------------------
projects / pspp-builds.git / commitdiff