Commit 98eb01d1 authored by simonpj's avatar simonpj

[project @ 1999-11-01 16:06:34 by simonpj]

Minor tweaks to intro, and description of RULES
parent cfd47515
%
% $Id: glasgow_exts.vsgml,v 1.17 1999/10/28 07:53:13 simonpj Exp $
% $Id: glasgow_exts.vsgml,v 1.18 1999/11/01 16:06:34 simonpj Exp $
%
% GHC Language Extensions.
%
......@@ -2085,9 +2085,14 @@ This rule will cause the compiler to go into an infinite loop.
<item> GHC currently uses a very simple, syntactic, matching algorithm
for matching a rule LHS with an expression. It seeks a substitution
which makes the LHS and expression syntactically equal modulo: alpha
conversion, and (I think) eta conversion. But not beta conversion (that's
called higher-order matching).
which makes the LHS and expression syntactically equal modulo alpha
conversion. The pattern (rule), but not the expression, is eta-expanded if
necessary. (Eta-expanding the epression can lead to laziness bugs.)
But not beta conversion (that's called higher-order matching).
<p>
Matching is carried out on GHC's intermediate language, which includes
type abstractions and applications. So a rule only matches if the
types match too. See Section <ref name="Specialisation" id="rule-spec"> below.
<item> GHC keeps trying to apply the rules as it optimises the program.
For example, consider:
......@@ -2184,6 +2189,7 @@ If you want to write your own good consumers or producers, look at the
Prelude definitions of the above functions to see how to do so.
<sect2>Specialisation
<label id="rule-spec">
<p>
Rewrite rules can be used to get the same effect as a feature
......
......@@ -3,8 +3,12 @@
<p>
This is a guide to using the Glasgow Haskell compilation (GHC) system.
It is a batch compiler for the Haskell~1.4 language, with support for
It is a batch compiler for the Haskell~98 language, with support for
various Glasgow-only extensions.
In this document, we assume that GHC has been installed at your site
as @ghc@. A separate document, ``Building and Installing the
Glasgow Functional Programming Tools Suite'',
describes how to install @ghc@.
Many people will use GHC very simply: compile some
modules---@ghc -c -O Foo.hs Bar.hs@; and link them---
......@@ -17,8 +21,7 @@ ghc -c -O -fno-foldr-build -dcore-lint -fvia-C -ddump-simpl Foo.lhs
</verb></tscreen>
Stay tuned---all will be revealed!
In this document, we assume that GHC has been installed at your site
as @ghc@. The rest of this section provide some tutorial information
The rest of this section provide some tutorial information
on batch-style compilation; if you're familiar with these concepts
already, then feel free to skip to the next section.
......
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