Extraction from streams #25
@ -42,10 +42,13 @@ context-free syntax
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Ex.EscString = STRING
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Ex.EscString = STRING
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Ex.Stream = <stream>
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Ex.Stream = <stream>
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Ex.Sum = <<Ex> + <Ex>> {left}
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Ex.Sum = <<Ex> + <Ex>> {left}
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Ex.Concat = <<Ex> ++ <Ex>> {left}
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Ex.Gets = [[Ex] << [Ex]] {left}
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Ex.Gets = [[Ex] << [Ex]] {left}
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Ex.DefGets = [<<< [Ex]]
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Ex.DefGets = [<<< [Ex]]
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Ex.To = [[Ex] >> [Ex]] {left}
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Ex.To = [[Ex] >> [Ex]] {left}
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Ex.DefTo = [[Ex] >>>]
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Ex.DefTo = [[Ex] >>>]
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Ex.Emits = <<Ex>!>
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Ex.DefEmits = <!!>
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Ex = <(<Ex>)> {bracket}
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Ex = <(<Ex>)> {bracket}
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@ -53,7 +56,7 @@ context-free priorities
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Ex.To
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Ex.To
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> Ex.DefTo
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> Ex.DefTo
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> Ex.Sum
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> {Ex.Sum Ex.Concat}
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> Ex.DefGets
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> Ex.DefGets
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> Ex.Gets,
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> Ex.Gets,
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@ -294,3 +294,36 @@ test emit_several_default [[
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]] parse succeeds
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]] parse succeeds
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/** writes
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/** writes
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3399677527121313*/
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3399677527121313*/
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/** md
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### Streams are bidirectional
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So far we have only sent items to a stream. But we can extract them from
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streams as well, with the `!` postfix operator. `!!` all by itself abbreviates
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`stream!`, i.e., extraction from the standard stream. For example,
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```fostr
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**/
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/** md */ test custom_hw [[
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<<< "What is your name?\n"
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<<< 'Hello, ' ++ !!
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]] /* **/
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parse to TopLevel(Sequence([
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DefGets(EscString("\"What is your name?\n\"")),
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DefGets(Concat(LitString("'Hello, '"),DefEmits()))
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]))
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/** accepts
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Kilroy
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**/
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/** writes
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What is your name?
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Hello, Kilroy**/
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/** md
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```
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queries users for their name and then writes a customized greeting. It also
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illustratesthe use of `++` for string concatenation, as opposed to `+` for
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(numerical) addition.
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**/
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@ -17,6 +17,7 @@ rules
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defStream: DefGets(x) -> Gets(Stream(), x)
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defStream: DefGets(x) -> Gets(Stream(), x)
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defStream: DefTo(x) -> To(x, Stream())
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defStream: DefTo(x) -> To(x, Stream())
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defStream: DefEmits() -> Emits(Stream())
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strategies
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strategies
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@ -8,6 +8,8 @@ rules
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def gets(self, v):
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def gets(self, v):
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print(v, file=sys.stdout, end='')
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print(v, file=sys.stdout, end='')
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return self
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return self
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def emit(self):
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return input()
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def to(data,strm):
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def to(data,strm):
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strm.gets(data)
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strm.gets(data)
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return data
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return data
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@ -21,8 +23,10 @@ rules
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py: LitString(x) -> $[r[x]]
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py: LitString(x) -> $[r[x]]
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py: EscString(x) -> x
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py: EscString(x) -> x
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py: Sum(x,y) -> $[[x] + [y]]
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py: Sum(x,y) -> $[[x] + [y]]
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py: Concat(x,y) -> $[[x] + [y]]
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py: Gets(x, y) -> $[[x].gets([y])]
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py: Gets(x, y) -> $[[x].gets([y])]
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py: To(x, y) -> $[to([x],[y])]
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py: To(x, y) -> $[to([x],[y])]
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py: Emits(x) -> $[[x].emit()]
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py: Terminate(x) -> $[[x];]
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py: Terminate(x) -> $[[x];]
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py: Sequence(l) -> <join(|"\n")>l
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py: Sequence(l) -> <join(|"\n")>l
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@ -222,6 +222,13 @@ This pattern lets us specify error messages.
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type_Ex(e2) == STREAM() | error $[Items may only be sent to Streams.]@e2.
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type_Ex(e2) == STREAM() | error $[Items may only be sent to Streams.]@e2.
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/* **/
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/* **/
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ty_Ex(Concat(e1, e2)) = STRING() :-
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type_Ex(e1) == STRING() | error $[Expression [e1] not String in concat.]@e1,
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type_Ex(e2) == STRING() | error $[Expression [e2] not String in concat.]@e2.
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ty_Ex(Emits(e)) = STRING() :- // At the moment, only stream is stdio
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type_Ex(e) == STREAM() | error $[Only Streams may emit items.]@e.
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/** md
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/** md
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```
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```
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