95 lines
2.8 KiB
Scheme
95 lines
2.8 KiB
Scheme
(library
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(regex)
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(export compile-rx)
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(import (chezscheme)
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(matchable))
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;; Simple regex library, because it's friday and I'm bored.
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;; Playing with the ideas in: https://swtch.com/~rsc/regexp/regexp2.html
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;; which reminded me of reading through the source code to Sam in '93.
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;; Rather than parsing a string we'll use expressions.
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;; (lit <string>)
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;; (cat rx1 rx2)
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;; (alt rx1 rx2)
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;; (opt rx)
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;; (star rx)
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;; (plus rx)
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;;
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;; The expressions get compile-rxd into a vector of vm instructions.
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;; (char c)
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;; (match)
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;; (jmp x)
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;; (split x y)
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;; instructions are closures that manipulate the thread
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;; FIXME: slow
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(define (append-instr code . i)
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(append code i))
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(define (label-instr l)
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`(label ,l))
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(define (jmp-instr l)
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`(jmp ,l))
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(define (char-instr c)
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`(char ,c))
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(define (split-instr l1 l2)
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`(split ,l1 ,l2))
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(define (match-instr)
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'(match))
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(define (label-code label code)
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(cons (label-instr label) code))
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;; Compiles to a list of labelled instructions that can later be flattened
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;; into a linear sequence.
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(define (compile-rx exp)
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(match exp
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(('lit str)
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(map char-instr (string->list str)))
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(('cat rx1 rx2)
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(append (compile-rx rx1) (compile-rx rx2)))
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(('alt rx1 rx2)
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(let ((label1 (gensym))
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(label2 (gensym)))
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(let ((c1 (label-code label1 (compile-rx rx1)))
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(c2 (label-code label2 (compile-rx rx2))))
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(cons (split-instr label1 label2)
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(append c1 c2)))))
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(('opt rx)
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(let ((head (gensym))
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(tail (gensym)))
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(cons (split-instr head tail)
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(label-code head (append-instr (compile-rx rx)
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(label-instr tail))))))
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(('star rx)
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(let ((head (gensym))
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(tail (gensym)))
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(cons (split-instr head tail)
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(label-code head (append-instr (compile-rx rx)
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(jmp-instr head)
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(label-instr tail))))))
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(('plus rx)
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(let ((head (gensym))
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(tail (gensym)))
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(label-code head
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(append-instr (compile-rx rx)
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(split-instr head tail)
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(label-instr tail)))))))
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;; A 'thread' consists of an index into the instructions. A 'bundle' holds
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;; the current threads. Note there cannot be more threads than instructions,
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;; so a bundle is represented as a bitvector the same length as the
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;; instructions. Threads are run in lock step, all taking the same input.
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)
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