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61 lines
2.3 KiB
Racket
61 lines
2.3 KiB
Racket
#lang racket/base
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(require racket/contract/base)
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(provide
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(struct-out cf-grammar)
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(struct-out cf-production-rule)
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(contract-out
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[cf-grammar-start-rules (-> cf-grammar? (set/c cf-production-rule? #:kind 'immutable))]
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[make-cf-grammar (-> #:rules (sequence/c cf-production-rule?) #:start-symbol any/c cf-grammar?)]
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[make-cf-production-rule
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(-> #:nonterminal any/c #:substitution (sequence/c grammar-symbol?) #:action semantic-action?
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cf-production-rule?)]))
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(require racket/sequence
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racket/set
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rebellion/collection/vector
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yaragg/base/derivation
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yaragg/base/semantic-action
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yaragg/base/symbol)
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;@----------------------------------------------------------------------------------------------------
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;; Parsing takes a (Grammar T S A) and a sequence of (Token T V) and produces a set of
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;; (Parser-Derivation V A) (also called a "parse forest"). A grammar contains an immutable
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;; vector of (Context-Free-Production-Rule T S A) and a start symbol of type S.
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;; T: the terminals the grammar parses. Corresponds to the type field of the input tokens.
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;; S: the nonterminals the grammar rules are defined in terms of.
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;; A: the labels that grammar rules may have attached to them via the (Label-Action A) semantic
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;; action. These show up in parse tree branches, and can be used to determine which production
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;; rule produced a derivation.
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(struct cf-grammar (rules start-symbol) #:transparent)
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(define (cf-grammar-start-rules grammar)
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(define start (cf-grammar-start-symbol grammar))
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(for/set ([rule (in-vector (cf-grammar-rules grammar))]
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#:when (equal? (cf-production-rule-nonterminal rule) start))
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rule))
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;; A (Context-Free-Production-Rule T S A) contains a nonterminal symbol of type S, semantic action of
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;; type (Semnatic-Action A), and a substitution sequence of (Grammar-Symbol T S) values, stored in an
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;; immutable vector.
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(struct cf-production-rule (nonterminal action substitution) #:transparent)
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(define (make-cf-grammar #:rules rules #:start-symbol start)
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(cf-grammar (sequence->vector rules) start))
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(define (make-cf-production-rule #:nonterminal nonterminal
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#:action action
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#:substitution substitution)
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(cf-production-rule nonterminal action (sequence->vector substitution)))
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