author | Tony Garnock-Jones <tonygarnockjones@gmail.com> |
Wed, 16 Jan 2019 17:15:58 +0000 | |
changeset 438 | 1fe179d53161 |
parent 282 | 36ad47fbeb8d |
permissions | -rw-r--r-- |
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1 |
19 May 2009 |
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4 |
Unify OMeta with pattern matching. Support extensible pattern matching. |
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Input stream can't hold semantic-values without extra stack |
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discipline, because inputs and semantic-values are not of the same |
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type. |
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The wildcard operator, _, is of type token -> semantic-value |
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Running example: parenthesised n-ary addition (into binary addition) |
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e() --> e0():a '+' e0():b ^(a + b) / e0() |
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paren(p) --> '(' p():a ')' ^a |
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e0() --> paren(e) / num() |
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num() --> '1' ^1 / '2' ^2 / '3' ^3 / ... |
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define :e() -> { a=:e0() '+' b=:e0() -> a + b; |
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a=:e0() -> a }; |
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define :paren(p) -> { '(' a=p() ')' -> a } |
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define :e0() -> { a=:paren(:e) -> a; |
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a=:num() -> a } |
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define :num() -> { '1' -> 1; '2' -> 2; '3' -> 3; ... } |
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8 July 2009 |
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I should have written something about where the cutpoints in the |
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backtracking should go. The issue is to do with autocurrying: if too |
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many or too few arguments are supplied, how are the pattern-matching |
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continuations wired up? |
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7 August 2009 |
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Input streams have two manifestations: from the POV of the lookup |
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driver, streams *can* be empty, but from the POV of a *parser*, they |
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*cannot* be empty: this is the essence of autocurrying. So when the |
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lookup driver starts running, it examines its input stream. If the |
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stream is empty, it returns the parser without further effort. [TODO: |
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figure out what happens to the "receiver" (as distinct from "via") in |
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this case!] If the stream is nonempty, it *wraps* it in an *infinite |
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stream* guise, and if the wrapped stream ever internally runs out of |
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input, a curried function is returned to the caller with a parameter |
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(dynamic variable) used to speculatively extend the input stream as |
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subsequent input comes available. |
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The curried-function representation needs to be a bit special: a |
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partial match. This may address the TODO about what happens to the |
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receiver. |
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Re: cutpoints -- a commit is a cutpoint, and they happen on the arrows |
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in functions: { .a .b -> .c } has a cutpoint after the .b has been |
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matched. Essentially any transition from a LHS to an RHS is a |
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cutpoint. This is involved in what happens to "receiver" vs "via" in |
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lookup, too. |
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Here are some notes from a couple of weeks ago that I made in my graph |
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pad: |
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- functions are implicit 'or's of 'seq's by default. |
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- stream * kt * kf -> () |
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- currying:: model stream as CPS pair. Then when input runs out, |
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nonlocal exit to code that conses an intermediate lambda and waits |
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for more input? Problematic because during parsing it's often the |
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next unexpected token that causes the parser to switch to a more |
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appropriate clause -- and here we lack the means to terminate |
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pattern matching! |
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- therefore omit currying?? no. Alternative: treat every object as |
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"actor"? Messages stream into the actor |
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- matcher: stream kt kf ---- stream is always infinite! Will never |
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report "empty" to the parser and may suspend the parser pending |
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further messages |
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- Every object is therefore a parser. |
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Thoughts on the TODO from above about "receiver" vs "via": Because |
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sequences used to be seen as actually sugar for real curried |
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procedures, and the interstitial procedures would be |
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non-self-capturing, we can ignore supplied receivers to intermediate |
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curried procedures! |
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That means that the "receiver" supplied at the first, original |
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"lookup" needs to be preserved through all intermediate curryings, for |
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use at the time the "apply" is done. Any "receiver"s supplied after |
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that first one are to be ignored. |
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10 August 2009 |
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Lining up OMeta and eTNG: |
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106 |
or :: implicit; clauses in a function |
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107 |
seq :: implicit; part of currying |
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108 |
exactly :: (lit) |
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109 |
anything :: (discard) |
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110 |
bind :: (bind), but eTNG doesn't do nested patterns here yet |
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111 |
sequence :: could be a function? a bit like tuple-matching? |
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112 |
nest :: needs to be provided? |
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113 |
not :: - |
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114 |
follow :: - |
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115 |
many :: - |
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116 |
many1 :: - |
282
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117 |
|
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118 |
|
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119 |
14 August 2009 |
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120 |
--------------------------------------------------------------------------- |
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121 |
|
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122 |
Objects need to present alternately as *interpreter* and |
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123 |
*interpretee*. Interpreters are in the pattern-match role; |
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124 |
interpretees are data (ADTs etc). Data and co-data? |
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125 |
|
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126 |
So presenting as an interpreter is straightforward. Presenting as data |
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127 |
is trickier. Ordinary expressions combine objects, interpreter in head |
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128 |
position and syntax in non-head positions. On the pattern-matching |
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129 |
side, the matching logic embodies the interpreter. The matching logic |
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130 |
examines the offered data either *reflectively* or *interactively*. |
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131 |
|
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132 |
(Ha - where COLA has a recursive lookup that is ground-out on the |
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133 |
primitive lookup object, we here have a recursive streaming-of-data |
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134 |
that needs to be ground-out on primitive data streams! (as in, |
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135 |
messages should be able to be Real Streams With Behaviour, but in |
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136 |
order to be well-founded, some fake/primitive implementation needs to |
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137 |
be available.) |
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138 |
|
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139 |
Reflective examination actually feels pretty interactive, just on the |
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140 |
object's metaobject. Is representation (i.e. normal meta stuff) the |
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141 |
same as data/interpretee in this sense? After all, a pattern-matcher |
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142 |
may wish to examine an object's structure either at a physical level |
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143 |
or a logical level. Normal meta stuff is the physical, representative, |
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144 |
stuff; this interpretee idea is the logical level. |
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145 |
|
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146 |
Objects should be able to control how they are presented as data. One |
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147 |
possibility is a two-stage menu/inject, where the interpreter offers a |
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148 |
menu of contexts and the datum injects a context into the menu, |
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149 |
backing off and trying an alternative context on DNU. The symmetric |
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150 |
case works just as well, though, where the datum presents a menu and |
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151 |
the interpreter injects into it. This is effectively multiple dispatch |
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152 |
:-( |
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153 |
|
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154 |
-- an interpreter menu |
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155 |
-- context representation-pattern |
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156 |
{ .stream -> { .pair head tail -> ...; |
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157 |
.nil -> ... }; |
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158 |
.tuple -> { length -> ... } } |
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159 |
|
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160 |
This is also really similar to HTTP content negotiation. |
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161 |
|
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162 |
Actually on second thoughts perhaps it's better for the interpreter to |
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163 |
inject a preferred interpretation into the datum, and have it answer |
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164 |
either a representation under that interpretation, or DNU. |
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165 |
|
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166 |
-- data menu for cons |
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167 |
{ .stream k -> k .pair head tail; |
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168 |
.tuple k -> k 2 head tail } |
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169 |
|
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170 |
-- data menu for nil |
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171 |
{ .stream k -> k .nil; |
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172 |
.tuple k -> k 0 } |
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173 |
|
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174 |
Is using DNU appropriate here, or is an explicit failure-k better? |
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175 |
|
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176 |
{ .stream kt kf -> kt .pair head tail; |
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177 |
.tuple kt kf -> kt 2 head tail; |
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178 |
_ kt kf -> kf () } |