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| -rw-r--r-- | doc/trmacros.txt | 275 | ||||
| -rw-r--r-- | web/nimrod.ini | 2 |
2 files changed, 1 insertions, 276 deletions
diff --git a/doc/trmacros.txt b/doc/trmacros.txt deleted file mode 100644 index d5ad74e6e..000000000 --- a/doc/trmacros.txt +++ /dev/null @@ -1,275 +0,0 @@ -========================================================= - Term rewriting macros for Nimrod -========================================================= - -:Author: Andreas Rumpf - -Term rewriting macros are macros or templates that have not only a *name* but -also a *pattern* that is searched for after the semantic checking phase of -the compiler: This means they provide an easy way to enhance the compilation -pipeline with user defined optimizations: - -.. code-block:: nimrod - template optMul{`*`(a, 2)}(a: int): int = a+a - - let x = 3 - echo x * 2 - -The compiler now rewrites ``x * 2`` as ``x + x``. The code inside the -curlies is the pattern to match against. The operators ``*``, ``**``, -``|``, ``~`` have a special meaning in patterns if they are written in infix -notation, so to match verbatim against ``*`` the ordinary function call syntax -needs to be used. - - -Unfortunately optimizations are hard to get right and even the tiny example -is **wrong**: - -.. code-block:: nimrod - template optMul{`*`(a, 2)}(a: int): int = a+a - - proc f(): int = - echo "side effect!" - result = 55 - - echo f() * 2 - -We cannot duplicate 'a' if it denotes an expression that has a side effect! -Fortunately Nimrod supports side effect analysis: - -.. code-block:: nimrod - template optMul{`*`(a, 2)}(a: int{noSideEffect}): int = a+a - - proc f(): int = - echo "side effect!" - result = 55 - - echo f() * 2 # not optimized ;-) - -So what about ``2 * a``? We should tell the compiler ``*`` is commutative. We -cannot really do that however as the following code only swaps arguments -blindly: - -.. code-block:: nimrod - template mulIsCommutative{`*`(a, b)}(a, b: int): int = b*a - -What optimizers really need to do is a *canonicalization*: - -.. code-block:: nimrod - template canonMul{`*`(a, b)}(a: int{lit}, b: int): int = b*a - -The ``int{lit}`` parameter pattern matches against an expression of -type ``int``, but only if it's a literal. - - - -Parameter constraints -===================== - -The parameter constraint expression can use the operators ``|`` (or), -``&`` (and) and ``~`` (not) and the following predicates: - -=================== ===================================================== -Predicate Meaning -=================== ===================================================== -``atom`` The matching node has no children. -``lit`` The matching node is a literal like "abc", 12. -``sym`` The matching node must be a symbol (a bound - identifier). -``ident`` The matching node must be an identifier (an unbound - identifier). -``call`` The matching AST must be a call/apply expression. -``lvalue`` The matching AST must be an lvalue. -``sideeffect`` The matching AST must have a side effect. -``nosideeffect`` The matching AST must have no side effect. -``param`` A symbol which is a parameter. -``genericparam`` A symbol which is a generic parameter. -``module`` A symbol which is a module. -``type`` A symbol which is a type. -``var`` A symbol which is a variable. -``let`` A symbol which is a ``let`` variable. -``const`` A symbol which is a constant. -``result`` The special ``result`` variable. -``proc`` A symbol which is a proc. -``method`` A symbol which is a method. -``iterator`` A symbol which is an iterator. -``converter`` A symbol which is a converter. -``macro`` A symbol which is a macro. -``template`` A symbol which is a template. -``field`` A symbol which is a field in a tuple or an object. -``enumfield`` A symbol which is a field in an enumeration. -``forvar`` A for loop variable. -``label`` A label (used in ``block`` statements). -``nk*`` The matching AST must have the specified kind. - (Example: ``nkIfStmt`` denotes an ``if`` statement.) -``alias`` States that the marked parameter needs to alias - with *some* other parameter. -``noalias`` States that *every* other parameter must not alias - with the marked parameter. -=================== ===================================================== - -The ``alias`` and ``noalias`` predicates refer not only to the matching AST, -but also to every other bound parameter; syntactially they need to occur after -the ordinary AST predicates: - -.. code-block:: nimrod - template ex{a = b + c}(a: int{noalias}, b, c: int) = - # this transformation is only valid if 'b' and 'c' do not alias 'a': - a = b - inc a, b - - -Pattern operators -================= - -The operators ``*``, ``**``, ``|``, ``~`` have a special meaning in patterns -if they are written in infix notation. - - -The ``|`` operator ------------------- - -The ``|`` operator if used as infix operator creates an ordered choice: - -.. code-block:: nimrod - template t{0|1}(): expr = 3 - let a = 1 - # outputs 3: - echo a - -The matching is performed after the compiler performed some optimizations like -constant folding, so the following does not work: - -.. code-block:: nimrod - template t{0|1}(): expr = 3 - # outputs 1: - echo 1 - -The reason is that the compiler already transformed the 1 into "1" for -the ``echo`` statement. However, a term rewriting macro should not change the -semantics anyway. In fact they can be deactived with the ``--patterns:off`` -command line option or temporarily with the ``patterns`` pragma. - - -The ``{}`` operator -------------------- - -A pattern expression can be bound to a pattern parameter via the ``expr{param}`` -notation: - -.. code-block:: nimrod - template t{(0|1|2){x}}(x: expr): expr = x+1 - let a = 1 - # outputs 2: - echo a - - -The ``~`` operator ------------------- - -The ``~`` operator is the **not** operator in patterns: - -.. code-block:: nimrod - template t{x = (~x){y} and (~x){z}}(x, y, z: bool): stmt = - x = y - if x: x = z - - var - a = false - b = true - c = false - a = b and c - echo a - - -The ``*`` operator ------------------- - -The ``*`` operator can *flatten* a nested binary expression like ``a & b & c`` -to ``&(a, b, c)``: - -.. code-block:: nimrod - var - calls = 0 - - proc `&&`(s: varargs[string]): string = - result = s[0] - for i in 1..len(s)-1: result.add s[i] - inc calls - - template optConc{ `&&` * a }(a: string): expr = &&a - - let space = " " - echo "my" && (space & "awe" && "some " ) && "concat" - - # check that it's been optimized properly: - doAssert calls == 1 - - -The second operator of `*` must be a parameter; it is used to gather all the -arguments. The expression ``"my" && (space & "awe" && "some " ) && "concat"`` -is passed to ``optConc`` in ``a`` as a special list (of kind ``nkArgList``) -which is flattened into a call expression; thus the invocation of ``optConc`` -produces: - -.. code-block:: nimrod - `&&`("my", space & "awe", "some ", "concat") - - -The ``**`` operator -------------------- - -The ``**`` is much like the ``*`` operator, except that it gathers not only -all the arguments, but also the matched operators in reverse polish notation: - -.. code-block:: nimrod - import macros - - type - TMatrix = object - dummy: int - - proc `*`(a, b: TMatrix): TMatrix = nil - proc `+`(a, b: TMatrix): TMatrix = nil - proc `-`(a, b: TMatrix): TMatrix = nil - proc `$`(a: TMatrix): string = result = $a.dummy - proc mat21(): TMatrix = - result.dummy = 21 - - macro optM{ (`+`|`-`|`*`) ** a }(a: TMatrix): expr = - echo treeRepr(a) - result = newCall(bindSym"mat21") - - var x, y, z: TMatrix - - echo x + y * z - x - -This passes the expression ``x + y * z - x`` to the ``optM`` macro as -an ``nnkArgList`` node containing:: - - Arglist - Sym "x" - Sym "y" - Sym "z" - Sym "*" - Sym "+" - Sym "x" - Sym "-" - -(Which is the reverse polish notation of ``x + y * z - x``.) - - -Parameters -========== - -Parameters in a pattern are type checked in the matching process. If a -parameter is of the type ``varargs`` it is treated specially and it can match -0 or more arguments in the AST to be matched against: - -.. code-block:: nimrod - template optWrite{ - write(f, x) - ((write|writeln){w})(f, y) - }(x, y: varargs[expr], f: TFile, w: expr) = - w(f, x, y) - diff --git a/web/nimrod.ini b/web/nimrod.ini index fc652c158..af9ac0cd9 100644 --- a/web/nimrod.ini +++ b/web/nimrod.ini @@ -36,7 +36,7 @@ UNIX. We don't believe this to be a coincidence. - Jeremy S. Anderson.""" [Documentation] -doc: "endb;intern;apis;lib;manual;tut1;tut2;nimrodc;overview;filters;trmacros" +doc: "endb;intern;apis;lib;manual;tut1;tut2;nimrodc;overview;filters" doc: "tools;c2nim;niminst;nimgrep;gc;estp;idetools;docgen;koch;backends.txt" pdf: "manual;lib;tut1;tut2;nimrodc;c2nim;niminst;gc" srcdoc2: "system.nim;impure/graphics;wrappers/sdl" |