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Adds the bracket postfix branch:
a[0] / a[i] / a[i+1] / m["key"] → (list :index OBJ IDX)
a[:] / a[1:] / a[:2] / a[1:2] / a[1:2:3] → (list :slice OBJ LOW HIGH MAX)
LOW/HIGH/MAX are AST nodes or nil for omitted indices. The 4th MAX
slot is only populated by the three-index full-slice form.
Two new lib/guest/ast.sx kit gaps surfaced (logged in plans/go-on-sx.md
Blockers):
* No :index node — universal across guests with arrays/maps.
* No :slice node — Python/Rust/Swift/JS/Ruby all need at minimum the
two-index form. Go's three-index variant is more specialised but
fits in the same shape with an optional fourth slot.
Parser is permissive on a[1::3] (strict Go rejects, but the type phase
can enforce the grammar; lexer/parser stays loose).
Chained (a[0][1]) and mixed-with-selector (a[0].field) cases work via
the existing left-associative postfix loop.
parse 61/61, total 190/190.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
236 lines
8.4 KiB
Plaintext
236 lines
8.4 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-call-args
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;; Parse comma-separated args inside (...). Caller has already
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;; consumed the opening "(". Consumes the closing ")".
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;; Returns a list of argument AST nodes.
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(fn
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()
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(let ((args (list)))
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(cond
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(and (= (gp-tok-type) "op") (= (gp-tok-value) ")"))
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(do (gp-advance!) args)
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:else
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(do
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(let ((first (gp-parse-expr 1)))
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(when (not (= first nil)) (append! args first)))
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(define
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gp-args-rest
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(fn
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()
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(cond
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(and (= (gp-tok-type) "op") (= (gp-tok-value) ","))
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(do
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(gp-advance!)
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(let ((arg (gp-parse-expr 1)))
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(when (not (= arg nil)) (append! args arg)))
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(gp-args-rest))
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(and (= (gp-tok-type) "op") (= (gp-tok-value) ")"))
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(gp-advance!)
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:else nil)))
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(gp-args-rest)
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args)))))
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(define
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gp-parse-bracket-expr
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;; Optional expression inside brackets — returns nil if next token
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;; is ':' or ']' (the slice "omitted" cases).
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(fn
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()
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(cond
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(and (= (gp-tok-type) "op")
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(or (= (gp-tok-value) ":") (= (gp-tok-value) "]")))
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nil
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:else (gp-parse-expr 1))))
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(define
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gp-parse-bracket
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;; Caller has consumed '['. Parses index or slice and ']'.
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;; x[i] → (list :index BASE i)
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;; x[a:b] → (list :slice BASE LOW HIGH nil) (LOW/HIGH may be nil)
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;; x[a:b:c] → (list :slice BASE LOW HIGH MAX)
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;; Returns the AST node based on BASE.
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(fn
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(base)
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(let ((low (gp-parse-bracket-expr)))
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(cond
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(and (= (gp-tok-type) "op") (= (gp-tok-value) "]"))
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(do (gp-advance!) (list :index base low))
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(and (= (gp-tok-type) "op") (= (gp-tok-value) ":"))
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(do
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(gp-advance!)
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(let ((high (gp-parse-bracket-expr)))
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(cond
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(and (= (gp-tok-type) "op") (= (gp-tok-value) "]"))
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(do (gp-advance!) (list :slice base low high nil))
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(and (= (gp-tok-type) "op") (= (gp-tok-value) ":"))
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(do
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(gp-advance!)
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(let ((maxe (gp-parse-bracket-expr)))
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(when (and (= (gp-tok-type) "op")
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(= (gp-tok-value) "]"))
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(gp-advance!))
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(list :slice base low high maxe)))
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:else (list :slice base low high nil))))
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:else base))))
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(define
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gp-parse-postfix
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;; Left-associative postfix loop on top of gp-parse-primary:
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;; x.field → (list :select x "field") — Go-specific
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;; f(args...) → (ast-app f args) — canonical
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;; x[i] → (list :index x i) — Go-specific
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;; x[a:b] → (list :slice x low high max) — Go-specific
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(fn
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()
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(let ((base (gp-parse-primary)))
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(gp-postfix-loop base))))
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(define
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gp-postfix-loop
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(fn
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(base)
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(cond
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(= base nil) nil
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:else
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(let ((tok (gp-cur)))
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(cond
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(and (= (get tok :type) "op") (= (get tok :value) "."))
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(do
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(gp-advance!)
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(let ((field-tok (gp-cur)))
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(cond
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(= (get field-tok :type) "ident")
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(do
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(gp-advance!)
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(gp-postfix-loop
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(list :select base (get field-tok :value))))
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:else base)))
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(and (= (get tok :type) "op") (= (get tok :value) "("))
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(do
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(gp-advance!)
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(gp-postfix-loop (ast-app base (gp-parse-call-args))))
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(and (= (get tok :type) "op") (= (get tok :value) "["))
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(do
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(gp-advance!)
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(gp-postfix-loop (gp-parse-bracket base)))
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:else base)))))
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(define
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gp-unary-ops
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;; Go spec § Operators: prefix unary, all higher precedence than
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;; any binary operator. <- is the channel receive form (send is a
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;; statement, not an expression, so never appears here as binary).
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(list "+" "-" "!" "^" "*" "&" "<-"))
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(define
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gp-parse-unary
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(fn
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()
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(let ((tok (gp-cur)))
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(cond
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(and (= (get tok :type) "op")
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(some (fn (u) (= u (get tok :value))) gp-unary-ops))
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(do
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(gp-advance!)
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(let ((operand (gp-parse-unary)))
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(cond
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(= operand nil) nil
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:else (ast-app (ast-var (get tok :value)) (list operand)))))
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:else (gp-parse-postfix)))))
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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-unary))) (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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