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gp-parse-expr / gp-pratt-loop implement classic Pratt climbing against go-precedence-table (entry shape from lib/guest/pratt.sx). The kit gives us pratt-op-lookup + accessors; the climbing loop itself stays per-language (per kit header — Lua and Prolog have opposite conventions). Left-associative ops raise the right-recursion min by 1; right- associative would keep prec. All Go binary operators are left-assoc. AST shape: a binary node is emitted as (ast-app (ast-var OP) [LHS RHS]) — canonical ast-app rather than a Go-specific binary node, since a future evaluator can recognise operator-named apps without losing information. Coverage: equal-prec left-to-right, * tighter than +, && tighter than ||, comparison tighter than &&, long left-assoc chains, mixed literal+ident operands. parse 26/26, total 155/155. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
103 lines
3.2 KiB
Plaintext
103 lines
3.2 KiB
Plaintext
;; lib/go/parse.sx — Go parser. Tokenises via go-tokenize (lib/go/lex.sx),
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;; builds canonical AST nodes per lib/guest/ast.sx, and uses
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;; pratt-op-lookup from lib/guest/pratt.sx for operator-precedence climbing.
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;;
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;; Slices so far:
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;; 1. Primary expressions — literal / identifier → ast-literal / ast-var
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;; 2. Binary operators — Pratt precedence climbing against
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;; go-precedence-table; binary application
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;; emitted as (ast-app (ast-var OP) [LHS RHS]).
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;;
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;; The climbing loop is per-language (see lib/guest/pratt.sx header on why)
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;; but the entry shape and lookup are shared.
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;;
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;; All scanner locals are gp- prefixed: SX host primitives silently shadow
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;; guest-language defines.
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(define
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go-precedence-table
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(list
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(list "*" 5 :left)
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(list "/" 5 :left)
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(list "%" 5 :left)
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(list "<<" 5 :left)
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(list ">>" 5 :left)
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(list "&" 5 :left)
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(list "&^" 5 :left)
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(list "+" 4 :left)
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(list "-" 4 :left)
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(list "|" 4 :left)
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(list "^" 4 :left)
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(list "==" 3 :left)
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(list "!=" 3 :left)
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(list "<" 3 :left)
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(list "<=" 3 :left)
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(list ">" 3 :left)
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(list ">=" 3 :left)
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(list "&&" 2 :left)
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(list "||" 1 :left)))
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(define
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go-parse
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(fn
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(src)
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(let
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((gp-tokens (go-tokenize src)) (gp-idx 0))
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(define gp-cur (fn () (nth gp-tokens gp-idx)))
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(define gp-advance! (fn () (set! gp-idx (+ gp-idx 1))))
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(define gp-tok-type (fn () (get (gp-cur) :type)))
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(define gp-tok-value (fn () (get (gp-cur) :value)))
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(define
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gp-parse-primary
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(fn
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()
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(let
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((ty (gp-tok-type)) (v (gp-tok-value)))
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(cond
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(or
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(= ty "int")
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(= ty "float")
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(= ty "imag")
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(= ty "string")
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(= ty "rune"))
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(do (gp-advance!) (ast-literal v))
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(= ty "ident")
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(do (gp-advance!) (ast-var v))
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:else nil))))
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(define
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gp-parse-expr
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(fn
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(min-prec)
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(let ((left (gp-parse-primary))) (gp-pratt-loop left min-prec))))
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(define
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gp-pratt-loop
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(fn
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(left min-prec)
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(cond
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(= left nil) nil
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:else
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(let
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((tok (gp-cur)))
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(cond
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(not (= (get tok :type) "op"))
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left
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:else (let
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((entry (pratt-op-lookup go-precedence-table (get tok :value))))
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(cond
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(= entry nil)
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left
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(< (pratt-op-prec entry) min-prec)
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left
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:else (do
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(gp-advance!)
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(let
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((next-min (if (= (pratt-op-assoc entry) :left) (+ (pratt-op-prec entry) 1) (pratt-op-prec entry))))
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(let
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((right (gp-parse-expr next-min)))
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(gp-pratt-loop
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(ast-app
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(ast-var (get tok :value))
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(list left right))
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min-prec)))))))))))
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(gp-parse-expr 1))))
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