diff options
Diffstat (limited to 'doc/manual/trmacros.txt')
| -rw-r--r-- | doc/manual/trmacros.txt | 18 |
1 files changed, 12 insertions, 6 deletions
diff --git a/doc/manual/trmacros.txt b/doc/manual/trmacros.txt index 90d01e475..5ff24a36a 100644 --- a/doc/manual/trmacros.txt +++ b/doc/manual/trmacros.txt @@ -43,6 +43,10 @@ Fortunately Nim supports side effect analysis: echo f() * 2 # not optimized ;-) +You can make one overload matching with a constraint and one without, and the +one with a constraint will have precedence, and so you can handle both cases +differently. + 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: @@ -105,8 +109,10 @@ Predicate Meaning with the marked parameter. =================== ===================================================== +Predicates that share their name with a keyword have to be escaped with +backticks: `` `const` ``. 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 +but also to every other bound parameter; syntactically they need to occur after the ordinary AST predicates: .. code-block:: nim @@ -144,7 +150,7 @@ constant folding, so the following does not work: 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`` +semantics anyway. In fact they can be deactivated with the ``--patterns:off`` command line option or temporarily with the ``patterns`` pragma. @@ -345,15 +351,15 @@ optimization for types that have copying semantics: ## puts a (key, value)-pair into `t`. The semantics of string require ## a copy here: let idx = findInsertionPosition(key) - t[idx] = key - t[idx] = val + t[idx].key = key + t[idx].val = val proc `[]=`*(t: var Table, key: string{call}, val: string{call}) = ## puts a (key, value)-pair into `t`. Optimized version that knows that ## the strings are unique and thus don't need to be copied: let idx = findInsertionPosition(key) - shallowCopy t[idx], key - shallowCopy t[idx], val + shallowCopy t[idx].key, key + shallowCopy t[idx].val, val var t: Table # overloading resolution ensures that the optimized []= is called here: |