parent
bb049984d5
commit
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1
Makefile
1
Makefile
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@ -20,6 +20,7 @@ path_src := src
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path_test := test
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test_apply := $(path_test)/apply/partial-test.xsl.apply \
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$(path_test)/apply/thrush-test.xsl.apply \
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$(path_test)/transform/apply-gen-test-in.xsl.apply
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.PHONY: check test
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@ -0,0 +1,146 @@
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<?xml version="1.0" encoding="utf-8"?>
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<!--
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Implementation of the Thrush combinator
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Copyright (C) 2014 LoVullo Associates, Inc.
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This file is part of hoxsl.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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The Thrush combinator is defined as @math{Txy = yx}.
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The Clojure macros @code{->} and @code{->>} (thread left/right) are
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popular Thrush-like implementations which result in a familiar
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pipeline-like style processing.
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This allows re-ordering applications in a way that humans actually
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think about them: left-to-right, not inside-out. Here's an example:
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@example
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sum( filter( get-values( $foo ), predicate() ) ).
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@end example
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This would be better represented as a pipeline, as is common in
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shell:
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@example
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get-values foo | filter predicate | sum
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@end example
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which we might express using @code{f:thrush} as
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@example
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f:thrush( get-values( $foo ),
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filter( predicate() ),
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sum() )
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@end example
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assuming that @code{filter} and @code{sum} above return dynamic
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function references.
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Above, @code{f:thrush} is equivalent to Clojure's @code{->>}; this
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is aliased to @code{f:thrushr} for clarity, if you'd prefer to use
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that. We also have @code{thrushl}, which is like Clojure's
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@code{->}, in that it maps the return value of a function to the
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@emph{first} parameter of the function following
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it. @code{f:thrush} is an alias of @code{f:thrushr} (rather than
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@code{f:thrushl}) because it is a natural fit with partial
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application (especially currying).
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OOP does similar using objects and method chaining:
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@example
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get-values( 'foo' )
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.filter( predicate() )
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.sum();
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@end example
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Indeed, the syntax @code{A.B(C)} is just syntactic sugar for
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applying @code{B} within the context of @code{A}—@code{B(A,C)}—which
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can be done using @code{f:thrushl}.
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-->
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<stylesheet version="2.0"
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xmlns="http://www.w3.org/1999/XSL/Transform"
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xmlns:xs="http://www.w3.org/2001/XMLSchema"
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xmlns:f="http://www.lovullo.com/hoxsl/apply"
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xmlns:_f="http://www.lovullo.com/hoxsl/apply/_priv">
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<import href="../apply.xsl" />
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<!--
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Alias of @code{f:thrushr}.
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-->
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<function name="f:thrush" as="item()">
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<param name="list" as="item()+" />
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<sequence select="f:thrushr( $list )" />
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</function>
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<!--
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Given a @var{list} of the form @code{(value, f1, f2, ...)}, return
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the result @code{...(f2(f1(value)))}
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If @var{list} consists only of @code{value}, simply return
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@code{value}. Any number of functions may be provided in @var{list}
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to form a pipeline; the result of the final application will be
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returned.
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All functions @emph{must} be unary; partial application should be
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used to provide beginning arguments. For example, this would yield
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the value @code{5}:
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@example
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<sequence select="f:thrush( 5, f:partial( f:add(), 4 ) )" />
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@end example
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See the @code{apply-gen} stylesheet for auto-generating curried
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functions to simplify the above partial application.
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-->
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<function name="f:thrushr" as="item()">
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<param name="list" as="item()+" />
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<sequence select="_f:thrushr-fold( subsequence( $list, 2 ),
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$list[ 1 ] )" />
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</function>
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<function name="_f:thrushr-fold" as="item()">
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<param name="fnref" as="item()*" />
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<param name="result" />
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<choose>
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<when test="empty( $fnref )">
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<sequence select="$result" />
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</when>
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<otherwise>
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<!-- FIXME: need abstraction -->
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<variable name="next" as="item()*"
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select="subsequence( $fnref,
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f:length( $fnref ) + 1 )" />
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<!-- map the next unary function to the previous result, then
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pass that result along for further mapping -->
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<sequence select="_f:thrushr-fold(
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$next,
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f:partial( $fnref, $result ) )" />
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</otherwise>
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</choose>
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</function>
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</stylesheet>
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@ -0,0 +1,78 @@
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<?xml version="1.0" encoding="utf-8"?>
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<!--
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Tests dynamic function application
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Copyright (C) 2014 LoVullo Associates, Inc.
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This file is part of hoxsl.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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-->
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<stylesheet version="2.0"
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xmlns="http://www.w3.org/1999/XSL/Transform"
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xmlns:xs="http://www.w3.org/2001/XMLSchema"
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xmlns:f="http://www.lovullo.com/hoxsl/apply"
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xmlns:foo="http://www.lovullo.com/_junk">
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<import href="../../src/apply/thrush.xsl" />
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<import href="thrush-test.xsl.apply" />
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<function name="foo:give-foo" as="node()">
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<param name="_" />
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<!-- little bunny... -->
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<foo:foo hop="forest"/>
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</function>
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<function name="foo:echo" as="item()">
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<param name="item" as="item()" />
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<sequence select="$item" />
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</function>
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<function name="foo:add1" as="xs:decimal">
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<param name="to" as="xs:decimal" />
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<sequence select="$to + 1" />
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</function>
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<function name="foo:add" as="xs:decimal">
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<param name="x" as="xs:decimal" />
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<param name="y" as="xs:decimal" />
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<sequence select="$x + $y" />
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</function>
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<function name="foo:add3" as="xs:decimal">
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<param name="x" as="xs:decimal" />
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<param name="y" as="xs:decimal" />
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<param name="z" as="xs:decimal" />
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<sequence select="$x + $y + $z" />
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</function>
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<function name="foo:double" as="xs:decimal">
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<param name="value" as="xs:decimal" />
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<sequence select="$value * 2" />
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</function>
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</stylesheet>
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@ -0,0 +1,118 @@
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<?xml version="1.0" encoding="utf-8"?>
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<!--
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Tests thrushing
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Copyright (C) 2014 LoVullo Associates, Inc.
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This file is part of hoxsl.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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-->
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<description xmlns="http://www.jenitennison.com/xslt/xspec"
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xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
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xmlns:x="http://www.jenitennison.com/xslt/xspec"
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xmlns:f="http://www.lovullo.com/hoxsl/apply"
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xmlns:foo="http://www.lovullo.com/_junk"
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stylesheet="thrush-test.xsl">
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<variable name="doc">
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<foo:parent name="foo">
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<foo:child />
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</foo:parent>
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</variable>
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<scenario label="f:thrushr function">
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<scenario label="with a single item">
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<call function="f:thrush">
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<param name="list" select="$doc/foo:child" />
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</call>
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<!-- we should retain context if the value wasn't copied -->
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<expect label="returns the value with context in tact"
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test="$x:result/parent::foo:parent/@name = 'foo'" />
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</scenario>
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<!-- first, we need to test that we actually get the return value
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of the second function -->
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<scenario label="with a second, unary function">
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<call function="f:thrush">
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<param name="list" select="$doc, foo:give-foo()" />
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</call>
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<expect label="provides results of second function">
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<foo:foo hop="forest" />
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</expect>
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<scenario label="value passed to second function">
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<call function="f:thrush">
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<param name="list" select="$doc/foo:child, foo:echo()" />
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</call>
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<expect label="should retain context"
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test="$x:result/parent::foo:parent/@name = 'foo'" />
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</scenario>
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</scenario>
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<!-- continue to test a simple case (unary) so that failures help to
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track down a problem, not confound further -->
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<scenario label="with multiple unary functions">
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<call function="f:thrush">
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<param name="list" select="1,
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foo:add1(),
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foo:add1(),
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foo:echo(),
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foo:double(),
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foo:echo()" />
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</call>
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<expect label="returns last application having passed previous
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results to each"
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test="$x:result = 6" />
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</scenario>
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<scenario label="with (n>1)-ary functions">
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<call function="f:thrush">
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<param name="list" select="1,
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f:apply( foo:add3(), 2, 3 )" />
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</call>
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<expect label="both previous result and partial arguments are
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passed"
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test="$x:result = 6" />
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</scenario>
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<scenario label="with a pipeline of (n>2) functions of varying
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arity">
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<call function="f:thrush">
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<param name="list"
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select="5,
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foo:add1(),
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foo:add( 3 ),
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foo:double(),
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f:apply( foo:add3(), 2, 1 )" />
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</call>
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<expect label="arguments are passed, ordered, through the
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pipeline to yield a final result"
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test="$x:result = 21" />
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</scenario>
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</scenario>
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</description>
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