DefineExpr - Revision history

Markm: /* Examples */

Markm — Sun, 04 Jan 2009 06:01:10 GMT

Examples

New page

[[DefineExpr]] is a [[Kernel-E]] node which matches a [[pattern]] against a specified value.

"def" <var>pattern</var> ("exit" <var>optExitExpr</var>)? ":=" <var>specimen</var>

Note that the syntax is identical to [[DefrecExpr]], the nonkernel expression which allows ''recursive'' definitions; DefineExpr rejects such uses.

== Fields ==

* <var>pattern</var> :[[Pattern]]
* <var>optExitExpr</var> :[[nullOk]]<nowiki>[</nowiki>[[EExpr]]]
* <var>specimen</var> :[[EExpr]]

== Scope ==

[[Node scope rules|seq]](<var>pattern</var>, <var>optExitExpr</var>, <var>specimen</var>)

Note that this order differs from the evaluation order; the static constraints make this possible without [[promise]]s.

== Evaluation ==

# If present, <var>optExitExpr</var> is evaluated.
# <var>specimen</var> is evaluated.
#<var>pattern</var> is matched against the result of <var>specimen</var>, with the result of <var>optExitExpr</var>, or [[throw]] if not present, as the ejector.

== Static constraints ==

* <var>specimen</var> may not use nouns bound by <var>pattern</var>. (See [[DefrecExpr]].)
* <var>optExitExpr</var> may not use nouns bound by <var>pattern</var>.
* <var>pattern</var> may not use nouns bound by <var>specimen</var>.
* <var>pattern</var> may not use nouns bound by <var>optExitExpr</var>.

== Examples ==

Simple uses with [[FinalPattern]], [[VarPattern]] and [[LiteralExpr]]:

? def pi := 3.14159
# value: 3.14159

? pi
# value: 3.14159

? def var x := 1
> x
# value: 1

? x := 2
> x
# value: 2

With optExitExpr specified, but making no difference:

? def x :int exit throw := 9
# value: 9

? x
# value: 9

? def x :String exit throw := 9
# problem: the int 9 doesn't coerce to a String

With optExitExpr different:

? def x :int exit def _(e) :void { print(e); throw("biff") } := 9
# value: 9

? def x :String exit def _(e) :void { print(e); throw("biff") } := 9
# stdout: problem: the int 9 doesn't coerce to a String

# problem: biff

Demonstration of the evaluation order:

? def [[ViaPattern|via]] (fn s,_ {println("patt"); throw("exit")}) x \
> exit (println("ejector"); null) \
> := (println("specimen"); 8)
# stdout: ejector
# specimen
# patt
#

# problem: exit

A bogus exit, which does not return when it should (this is [[throw.eject]] behavior):

XXX in [[E-on-Java]] this creates a note in the trace that the ejector returned and proceeds as if the ejector was null; the shown behavior is from [[E-on-CL]]; which to pick?

? def x :String exit def _(_) :void {} := 9
# problem: optEjector <__main$_> returned: null

Scope tests:

? {def y := 0; {def ==0 exit (def y := null) := y}}
# problem: null is not 0

XXX write more scope tests

[[Category:E language specification]]
[[Category:Kernel-E nodes]]

Markm: /* Scope */

Markm — Sun, 04 Jan 2009 05:57:50 GMT

Scope

←Older revision		Revision as of 05:57, 4 January 2009
Line 15:		Line 15:
	[[Node scope rules\|seq]](<var>pattern</var>, <var>optExitExpr</var>, <var>specimen</var>)		[[Node scope rules\|seq]](<var>pattern</var>, <var>optExitExpr</var>, <var>specimen</var>)

-	Note that this order differs from the evaluation order; the static constraints ~~prevent~~ this ~~from being impossible~~ without [[promise]]s.	+	Note that this order differs from the evaluation order; the static constraints make this possible without [[promise]]s.

	== Evaluation ==		== Evaluation ==

Kevin Reid: add tests, rename fields (MarkM agrees)

Kevin Reid — Sun, 04 Jan 2009 05:49:45 GMT

add tests, rename fields (MarkM agrees)

←Older revision		Revision as of 05:49, 4 January 2009
Line 1:		Line 1:
	[[DefineExpr]] is a [[Kernel-E]] node which matches a [[pattern]] against a specified value.		[[DefineExpr]] is a [[Kernel-E]] node which matches a [[pattern]] against a specified value.

-	"def" <var>pattern</var> ("exit" <var>~~optEjectorExpr~~</var>)? ":=" <var>~~rValue~~</var>	+	"def" <var>pattern</var> ("exit" <var>optExitExpr</var>)? ":=" <var>specimen</var>

	Note that the syntax is identical to [[DefrecExpr]], the nonkernel expression which allows ''recursive'' definitions; DefineExpr rejects such uses.		Note that the syntax is identical to [[DefrecExpr]], the nonkernel expression which allows ''recursive'' definitions; DefineExpr rejects such uses.
Line 8:		Line 8:

	* <var>pattern</var> :[[Pattern]]		* <var>pattern</var> :[[Pattern]]
-	* <var>~~optEjectorExpr~~</var> :[[nullOk]]<nowiki>[</nowiki>[[EExpr]]]	+	* <var>optExitExpr</var> :[[nullOk]]<nowiki>[</nowiki>[[EExpr]]]
-	* <var>~~rValue~~</var> :[[EExpr]]	+	* <var>specimen</var> :[[EExpr]]

	== Scope ==		== Scope ==

-	[[Node scope rules\|seq]](<var>pattern</var>, <var>~~optEjectorExpr~~</var>, <var>~~rValue~~</var>)	+	[[Node scope rules\|seq]](<var>pattern</var>, <var>optExitExpr</var>, <var>specimen</var>)
		+
		+	Note that this order differs from the evaluation order; the static constraints prevent this from being impossible without [[promise]]s.

	== Evaluation ==		== Evaluation ==

-	# If present, <var>~~optEjectorExpr~~</var> is evaluated.	+	# If present, <var>optExitExpr</var> is evaluated.
-	# <var>~~rValue~~</var> is evaluated.	+	# <var>specimen</var> is evaluated.
-	#<var>pattern</var> is matched against the result of <var>~~rValue~~</var>, with the result of <var>~~optEjectorExpr~~</var>, or [[throw]] if not present, as the ejector.	+	#<var>pattern</var> is matched against the result of <var>specimen</var>, with the result of <var>optExitExpr</var>, or [[throw]] if not present, as the ejector.

	== Static constraints ==		== Static constraints ==

-	* <var>~~rValue~~</var> may not use nouns bound by <var>pattern</var>. (See [[DefrecExpr]].)	+	* <var>specimen</var> may not use nouns bound by <var>pattern</var>. (See [[DefrecExpr]].)
-	* <var>~~optEjectorExpr~~</var> may not use nouns bound by <var>pattern</var>.	+	* <var>optExitExpr</var> may not use nouns bound by <var>pattern</var>.
-	* <var>pattern</var> may not use nouns bound by <var>~~rValue~~</var>.	+	* <var>pattern</var> may not use nouns bound by <var>specimen</var>.
-	* <var>pattern</var> may not use nouns bound by <var>~~optEjectorExpr~~</var>.	+	* <var>pattern</var> may not use nouns bound by <var>optExitExpr</var>.
		+
		+	== Examples ==
		+
		+	Simple uses with [[FinalPattern]], [[VarPattern]] and [[LiteralExpr]]:
		+
		+	? def pi := 3.14159
		+	# value: 3.14159
		+
		+	? pi
		+	# value: 3.14159
		+
		+	? def var x := 1
		+	> x
		+	# value: 1
		+
		+	? x := 2
		+	> x
		+	# value: 2
		+
		+	With optEjectorExpr specified, but making no difference:
		+
		+	? def x :int exit throw := 9
		+	# value: 9
		+
		+	? x
		+	# value: 9
		+
		+	? def x :String exit throw := 9
		+	# problem: the int 9 doesn't coerce to a String
		+
		+	With optEjectorExpr different:
		+
		+	? def x :int exit def _(e) :void { print(e); throw("biff") } := 9
		+	# value: 9
		+
		+	? def x :String exit def _(e) :void { print(e); throw("biff") } := 9
		+	# stdout: problem: the int 9 doesn't coerce to a String
		+
		+	# problem: biff
		+
		+	Demonstration of the evaluation order:
		+
		+	? def [[ViaPattern\|via]] (fn s,_ {println("patt"); throw("exit")}) x \
		+	> exit (println("ejector"); null) \
		+	> := (println("specimen"); 8)
		+	# stdout: ejector
		+	# specimen
		+	# patt
		+	#
		+
		+	# problem: exit
		+
		+	A bogus exit, which does not return when it should (this is [[throw.eject]] behavior):
		+
		+	XXX in [[E-on-Java]] this creates a note in the trace that the ejector returned and proceeds as if the ejector was null; the shown behavior is from [[E-on-CL]]; which to pick?
		+
		+	? def x :String exit def _(_) :void {} := 9
		+	# problem: optEjector <__main$_> returned: null
		+
		+	Scope tests:
		+
		+	? {def y := 0; {def ==0 exit (def y := null) := y}}
		+	# problem: null is not 0
		+
		+	XXX write more scope tests

	[[Category:E language specification]]		[[Category:E language specification]]
	[[Category:Kernel-E nodes]]		[[Category:Kernel-E nodes]]

Kevin Reid: specify DefineExpr

Kevin Reid — Sun, 04 Jan 2009 05:03:10 GMT

specify DefineExpr

←Older revision		Revision as of 05:03, 4 January 2009
Line 1:		Line 1:
	[[DefineExpr]] is a [[Kernel-E]] node which matches a [[pattern]] against a specified value.		[[DefineExpr]] is a [[Kernel-E]] node which matches a [[pattern]] against a specified value.

-	"def" <var>pattern</var> ("exit" <var>~~optExitExpr~~</var>)? ":=" <var>~~specimen~~</var>	+	"def" <var>pattern</var> ("exit" <var>optEjectorExpr</var>)? ":=" <var>rValue</var>

	Note that the syntax is identical to [[DefrecExpr]], the nonkernel expression which allows ''recursive'' definitions; DefineExpr rejects such uses.		Note that the syntax is identical to [[DefrecExpr]], the nonkernel expression which allows ''recursive'' definitions; DefineExpr rejects such uses.
Line 8:		Line 8:

	* <var>pattern</var> :[[Pattern]]		* <var>pattern</var> :[[Pattern]]
-	* <var>~~optExitExpr~~</var> :[[nullOk]]<nowiki>[</nowiki>[[EExpr]]]	+	* <var>optEjectorExpr</var> :[[nullOk]]<nowiki>[</nowiki>[[EExpr]]]
-	* <var>~~specimen~~</var> :[[EExpr]]	+	* <var>rValue</var> :[[EExpr]]

	== Scope ==		== Scope ==

-	[[Node scope rules\|seq]](<var>pattern</var>, <var>~~optExitExpr~~</var>, <var>~~specimen~~</var>)	+	[[Node scope rules\|seq]](<var>pattern</var>, <var>optEjectorExpr</var>, <var>rValue</var>)
-		+
-	~~Note that this order differs from the evaluation order; the static constraints make this possible without [[promise]]s.~~	+

	== Evaluation ==		== Evaluation ==

-	# If present, <var>~~optExitExpr~~</var> is evaluated.	+	# If present, <var>optEjectorExpr</var> is evaluated.
-	# <var>~~specimen~~</var> is evaluated.	+	# <var>rValue</var> is evaluated.
-	#<var>pattern</var> is matched against the result of <var>~~specimen~~</var>, with the result of <var>~~optExitExpr~~</var>, or [[throw]] if not present, as the ejector.	+	#<var>pattern</var> is matched against the result of <var>rValue</var>, with the result of <var>optEjectorExpr</var>, or [[throw]] if not present, as the ejector.

	== Static constraints ==		== Static constraints ==

-	* <var>~~specimen~~</var> may not use nouns bound by <var>pattern</var>. (See [[DefrecExpr]].)	+	* <var>rValue</var> may not use nouns bound by <var>pattern</var>. (See [[DefrecExpr]].)
-	* <var>~~optExitExpr~~</var> may not use nouns bound by <var>pattern</var>.	+	* <var>optEjectorExpr</var> may not use nouns bound by <var>pattern</var>.
-	* <var>pattern</var> may not use nouns bound by <var>~~specimen~~</var>.	+	* <var>pattern</var> may not use nouns bound by <var>rValue</var>.
-	* <var>pattern</var> may not use nouns bound by <var>~~optExitExpr~~</var>.	+	* <var>pattern</var> may not use nouns bound by <var>optEjectorExpr</var>.
-		+
-	~~== Examples ==~~	+
-		+
-	~~Simple uses with [[FinalPattern]], [[VarPattern]] and [[LiteralExpr]]:~~	+
-		+
-	~~? def pi := 3.14159~~	+
-	~~# value: 3.14159~~	+
-		+
-	~~? pi~~	+
-	~~# value: 3.14159~~	+
-		+
-	~~? def var x := 1~~	+
-	~~> x~~	+
-	~~# value: 1~~	+
-		+
-	~~? x := 2~~	+
-	~~> x~~	+
-	~~# value: 2~~	+
-		+
-	~~With optExitExpr specified, but making no difference:~~	+
-		+
-	~~? def x :int exit throw := 9~~	+
-	~~# value: 9~~	+
-		+
-	~~? x~~	+
-	~~# value: 9~~	+
-		+
-	~~? def x :String exit throw := 9~~	+
-	~~# problem: the int 9 doesn't coerce to a String~~	+
-		+
-	~~With optExitExpr different:~~	+
-		+
-	~~? def x :int exit def _(e) :void { print(e); throw("biff") } := 9~~	+
-	~~# value: 9~~	+
-		+
-	~~? def x :String exit def _(e) :void { print(e); throw("biff") } := 9~~	+
-	~~# stdout: problem: the int 9 doesn't coerce to a String~~	+
-		+
-	~~# problem: biff~~	+
-		+
-	~~Demonstration of the evaluation order:~~	+
-		+
-	~~? def [[ViaPattern\|via]] (fn s,_ {println("patt"); throw("exit")}) x \~~	+
-	~~> exit (println("ejector"); null) \~~	+
-	~~> := (println("specimen"); 8)~~	+
-	~~# stdout: ejector~~	+
-	~~# specimen~~	+
-	~~# patt~~	+
-	#	+
-		+
-	~~# problem: exit~~	+
-		+
-	~~A bogus exit, which does not return when it should (this is [[throw.eject]] behavior):~~	+
-		+
-	~~XXX in [[E-on-Java]] this creates a note in the trace that the ejector returned and proceeds as if the ejector was null; the shown behavior is from [[E-on-CL]]; which to pick?~~	+
-		+
-	~~? def x :String exit def _(_) :void {} := 9~~	+
-	~~# problem: optEjector <__main$_> returned: null~~	+
-		+
-	~~Scope tests:~~	+
-		+
-	~~? {def y := 0; {def ==0 exit (def y := null) := y}}~~	+
-	~~# problem: null is not 0~~	+
-		+
-	~~XXX write more scope tests~~	+

	[[Category:E language specification]]		[[Category:E language specification]]
	[[Category:Kernel-E nodes]]		[[Category:Kernel-E nodes]]