cvsuser 03/10/08 08:45:19
Modified: . MANIFEST Added: docs mmd.pod Log: Docs for the MMD subsystem Revision Changes Path 1.452 +1 -0 parrot/MANIFEST Index: MANIFEST =================================================================== RCS file: /cvs/public/parrot/MANIFEST,v retrieving revision 1.451 retrieving revision 1.452 diff -u -w -r1.451 -r1.452 --- MANIFEST 8 Oct 2003 12:58:13 -0000 1.451 +++ MANIFEST 8 Oct 2003 15:45:04 -0000 1.452 @@ -183,6 +183,7 @@ docs/intro.pod [main]doc docs/jit.pod [main]doc docs/memory_internals.pod [main]doc +docs/mmd.pod [main]doc docs/overview.pod [main]doc docs/parrot.pod [main]doc docs/parrot_assembly.pod [main]doc 1.1 parrot/docs/mmd.pod Index: mmd.pod =================================================================== =head1 TITLE Multimethod dispatch for binary opcode functions =head1 SYNOPSIS This system is set up to handle type-based dispatching for binary (i.e. two-arg) functions. This includes, though isn't necessarily limited to, binary operators such as addition or subtraction. =head1 DESCRIPTION The MMD system is straightforward, and currently must be explicitly invoked, for example by a vtable function. (We may reserve the right to use MMD in all circumstances, but currently do not) =head2 API For the purposes of the API, each MMD-able function is assigned a unique number which is used to find the right function table. This is the C<func_num> parameter in the following functions. While parrot isn't restricted to a predefined set of functions, it I<does> set things up so that all the binary vtable functions have a MMD table preinstalled for them, with default behaviour. =over 4 =item mmd_add_by_class(interp, func_num, left_class, right_class, funcptr) Adds a new MMD function C<funcptr> to the C<func_num> function table that will be invoked when the left parameter is of class C<left_class> and the right parameter is of class C<right_class>. Both classes are C<STRING *>s that hold the PMC class names for the left and right sides. If either class isn't yet loaded, Parrot will cache the information such that the function will be installed if at some point in the future both classes are available. Currently this is done by just assigning class numbers to the classes, which the classes will pick up and use if they're later loaded, but we may later put the functions into a deferred table that we scan when PMC classes are loaded. Either way, the function will be guaranteed to be installed when it's needed. The function table must exist, but if it is too small, it will automatically be expanded. =item mmd_register(interp, func_num, left_type, right_type, funcptr) Register a function C<funcptr> for MMD function tabe C<func_num> for classes C<left_type> and C<right_type>. The left and right types are C<INTVAL>s that represent the class ID numbers. The function table must exist, but if it is too small, it will automatically be expanded. Currently the MMD system doesn't handle inheritance and best match searching, as it assumes that all PMC types have no parent type. This can be considered a bug, and will be resolved at some point in the future. =item mmd_dispatch_pmc(interp, left, right, dest, func_num) Dispatch to a multimethod that "returns" a PMC. C<left>, C<right>, and C<dest> are all PMC pointers, while C<func_num> is the MMD table that should be used to do the dispatching. The MMD system will figure out which function should be called based on the types of C<left> and C<right> and call it, passing in C<left>, C<right>, and C<dest> like any other binary vtable function. This function has a void return type, like all the "take two PMCs, return a PMC" vtable functions do. =item STRING *mmd_dispatch_string(interp, left, right, func_num) Dispatch to a multimethod that returns a string. C<left> and C<right> are PMC pointers, while C<func_num> is the MMD table that should be used to do the dispatching. The function is responsible for creating the returned string. =item INTVAL mmd_dispatch_intval(interp, left, right, func_num) Like C<mmd_dispatch_string>, only it returns an INTVAL. =item FLOATVAL mmd_dispatch_numval(interp, left, right, func_num) Like C<mmd_dispatch_string>, only it returns a FLOATVAL. =item mmd_add_function(interp, func_num, default_func) Add a new function table to the list of functions the MMD system knows of. C<func_num> is the number of the new function, while C<default_func> is the function to be called when the system doesn't know which function it should call. (Because, for example, there hasn't been a function installed that matches the left and right types for a call) =back =head2 Constants The following constants are defined to identify function tables: =over 4 =item MMD_ADD Addition =item MMD_SUBTRACT Subtraction =item MMD_MULTIPLY Multiplication =item MMD_DIVIDE Division =item MMD_MOD Accurate modulus =item MMD_CMOD C-style modulus =item MMD_BAND Binary and =item MMD_BOR Binary or =item MMD_BXOR Binary xor =item MMD_BSL Bitshift left =item MMD_BSR Bitshift right =item MMD_CONCAT String concatenation =item MMD_LAND Short-circuiting logical and =item MMD_LOR Short-circuiting logical or =item MMD_LXOR Logical xor (not short-circuiting) =item MMD_REPEAT String repition =item MMD_NUMEQ Numeric equality =item MMD_STREQ String equality =item MMD_NUMCMP Numeric comparison =item MMD_STRCMP String comparison =item MMD_SOR Bitwise or of the string value =item MMD_SAND Bitwise and of the string value =item MMD_SXOR Bitwise xor of the string value =back =head2 Defaults By default functions are installed for all the functions that have constants associated with them. They are all functions suitable for calling with C<mmd_dispatch_pmc>. The math functions (add, subtract, multiply, and divide) all work on the float values of the left and right sides. The cmod function does a plan C-style mod (the C C<%> operator) on the integer value of the left and right sides. The mod function does an fmod on the float values of the two sides. The bitwise functions (and, or, xor, left shift, right shift) work on the integer values of the two sides. The concat function concatenates the string values of the left and right sides. The logical functions (and, or, xor) use the boolean values of the left and right sides to see whether they should set_pmc the destination to the left or right sides. The C<and> and C<or> functions short-circuit, C<xor> does not. The repeat function gets the string value of the left side and the integer value of the right. The numeric equal and numeric comparison functions work on the float values of both sides. The string equal and comparison functions work on the string values of both sides. The string bitwise ops (and, or, xor) take the string values of both sides and do bitwise operations on the resulting bitstring.
