The codec Lib — RFC 4648 Hex, Base64, Base64url, and URL Percent-Encoding

15.1. Why Does the codec Lib Exist? (The Real-World Problem & Ridgun Philosophy)

"Why do I need a codec lib written from scratch in pure Ridgun instead of just linking a legacy C library?"

That is the first question every systems engineer asks when meeting codec. And the answer captures the entire philosophy of ridgun-libs:

Let's be honest: nothing breaks a web integration faster than mixing up standard Base64 (+/=) with unpadded URL-safe Base64url (-_) inside a JWT, or building query strings by naive string concatenation.

The codec lib implements RFC 4648 (Hex, Base64, and URL-safe Base64url), RFC 3986 (URL percent-encoding and query encode / query decode), and lightweight RFC 8259 JSON builders and field extractors.

In a traditional ecosystem, solving CODEC tasks means pulling in external C dependencies, wrestling with raw pointers, opaque type conversions, unchecked exceptions, or unpredictable garbage-collector pauses. In Ridgun, the codec lib (src/main/ridgun/lib/codec.rg) tackles the problem with four non-negotiable principles:

1. Declare import codec (or import codec as alias) at the top of your file: every lib defines its module :: codec namespace, and under --strict multi-word functions are always called with natural spaces.
2. Chain your data pipelines left-to-right with ->: write input step one -> step two -> result, use (+ _ _ +) sequence masks to destructure tuples/lists, and omit _ = on sequential statements (or discard with -> ()).
3. Tail-Call Optimization (TCO): all internal loops in codec are tail-recursive and compile into native hardware loops using $O(1)$ stack space.
4. Deterministic Memory (RMM1 / RMM2): every intermediate allocation is reclaimed at the exact instruction where its last read finishes, with no Garbage Collector.

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15.2. Native Artifacts, Imports, and Complete codec API Catalog

In ridgun-libs, codec is a first-class lib located at src/main/ridgun/lib/codec.rg (domain CODEC). When built with stable bundle, it compiles into three native artifacts:

Artifact	Path	Purpose
Ridgun Bundle	target/bundles/codec.rglib	Portable distribution and direct import codec resolution
Compiled Archive	target/codec.rgc	Type-checked intermediate artifact verified by ridgunc
ELF64 Shared Object	target/libcodec.so	Native dynamic shared library with zero C or libc dependencies

Every lib declares its own namespace via module :: codec: simply write import codec (or import codec as alias) at the top and call its functions with natural spaces (my fn x) and left-to-right -> pipelines (x my fn -> result).

15.2.1. Summary of codec Functional Families

Signature / Function / Type	Purpose & Usage
hex encode / hex decode / hex is valid	Lowercase RFC 4648 hexadecimal encoding and validated decoding
base64 encode / base64 decode	Standard RFC 4648 §4 Base64 with = padding
base64url encode / base64url decode	URL-safe RFC 4648 §5 Base64url (-, _, unpadded)
url encode / url decode / query encode / query decode	RFC 3986 percent-encoding and k=v&... query string round-trips
json quote / json object / json get str / json get int	Fast zero-AST JSON serialization and top-level key lookup

15.2.2. Exhaustive Catalog of Types and Signatures in src/main/ridgun/lib/codec.rg

Below is the complete inventory of algebraic data types (type), mixfix operators (op ::), and function signatures (fn ::) defined in src/main/ridgun/lib/codec.rg (0 types, 0 operators, and 121 functions):

#	Function / Signature (fn ::)	Return Type
1	fn :: cd raw byte ub Int	String
2	fn :: cd raw byte Int	String
3	fn :: cd sb append3 String String	String String String String
4	fn :: cd sb append2 String String String	String String String String
5	fn :: cd sb append1 String String String String	String String String String
6	fn :: cd sb append String String String String String	String String String String
7	fn :: cd sb finish String String String String	String
8	fn :: cd lb append2 [String] [String] Int	[String] [String] [String] Int
9	fn :: cd lb append1 [String] [String] [String] Int	[String] [String] [String] Int
10	fn :: cd lb append String [String] [String] [String] Int	[String] [String] [String] Int
11	fn :: cd lb finish [String] [String] [String]	[String]
12	fn :: cd hex lut Int	String
13	fn :: cd hex up lut Int	String
14	fn :: cd b64 lut Int	String
15	fn :: cd b64url lut Int	String
16	fn :: cd match sub at String String Int Int Int	Bool
17	fn :: cd index of loop String String Int Int Int Int	Int
18	fn :: cd index of String String	Int
19	fn :: cd scan b end String Int	Int
20	fn :: cd scan b prev String Int	Int
21	fn :: cd scan ascii end String Int Int	Int
22	fn :: cd byte slice step String Int Int Int String String String String	String
23	fn :: cd byte slice loop String Int Int String String String String	String
24	fn :: cd byte slice check String Int Int Int Int	String
25	fn :: cd byte slice String Int Int	String
26	fn :: cd split char loop String String Int Int Int Int [String] [String] [String] Int	[String]
27	fn :: cd hex val Int	Int
28	fn :: cd valid hex loop String Int Int	Bool
29	fn :: cd is valid hex len String Int	Bool
30	fn :: is valid hex String	Bool
31	fn :: cd hex enc byte Int	String
32	fn :: cd hex enc loop String Int Int String String String String	String
33	fn :: hex encode String	String
34	fn :: cd hex dec loop String Int Int String String String String	String
35	fn :: hex decode String	String
36	fn :: cd b64 char String Int	String
37	fn :: cd b64 pad suffix String Bool	String
38	fn :: cd b64 enc step String Int String Bool Int String String String String	String
39	fn :: cd b64 enc rem String Int String Bool	String
40	fn :: base64 encode String	String
41	fn :: base64url encode String	String
42	fn :: cd b64 val Int	Int
43	fn :: cd strip one b64 pad String Int	String
44	fn :: cd strip b64 pad String Int	String
45	fn :: cd valid b64 body String Int Int	Bool
46	fn :: cd valid b64 raw String Int	Bool
47	fn :: is valid base64 String	Bool
48	fn :: cd b64 dec step String Int Int Int String String String String	String
49	fn :: cd b64 dec loop String Int Int	String
50	fn :: base64 decode String	String
51	fn :: base64url decode String	String
52	fn :: cd is unreserved Int	Bool
53	fn :: cd scan unres String String Int Int	Int
54	fn :: cd pct byte lut String Int	String
55	fn :: cd url enc step String String String Int Int Int String String String String	String
56	fn :: cd url enc loop String String String Int Int String String String String	String
57	fn :: url encode String	String
58	fn :: cd scan url plain String Int Int	Int
59	fn :: cd url dec pct String Int Int Int Int String String String String String	String
60	fn :: cd url dec step String Int Int Int String String String String	String
61	fn :: cd url dec loop String Int Int String String String String	String
62	fn :: url decode String	String
63	fn :: cd pair key (String String)	String
64	fn :: cd pair val (String String)	String
65	fn :: cd qs enc loop [String String] String String String String	String
66	fn :: query string encode [String String]	String
67	fn :: cd parse kv at String Int	String String
68	fn :: cd parse kv item String	String String
69	fn :: cd kv lb append2 [String String] [String String] Int	[String String] [String String] [String String] Int
70	fn :: cd kv lb append1 [String String] [String String] [String String] Int	[String String] [String String] [String String] Int
71	fn :: cd kv lb append (String String) [String String] [String String] [String String] Int	[String String] [String String] [String String] Int
72	fn :: cd parse qs list [String] [String String] [String String] [String String] Int	[String String]
73	fn :: cd strip leading q String	String
74	fn :: cd decode clean qs String	[String String]
75	fn :: query string decode String	[String String]
76	fn :: cd is json esc Int	Bool
77	fn :: cd scan json plain String Int Int	Int
78	fn :: cd json esc hex2 Int	String
79	fn :: cd json esc code ub Int	String
80	fn :: cd json esc code Int	String
81	fn :: cd json esc step String Int Int Int String String String String	String
82	fn :: cd json esc loop String Int Int String String String String	String
83	fn :: json escape String	String
84	fn :: cd json unesc char String Int Int	String
85	fn :: cd scan no backslash String Int Int	Int
86	fn :: cd json unesc cp Int Int	String Int
87	fn :: cd json unesc u4 Int Int Int Int Int	String Int
88	fn :: cd json unesc step String Int Int Int String String String String	String
89	fn :: cd json unesc loop String Int Int String String String String	String
90	fn :: json unescape String	String
91	fn :: json quote String	String
92	fn :: json int Int	String
93	fn :: json bool Bool	String
94	fn :: json null	String
95	fn :: cd join json loop [String] String String String String	String
96	fn :: cd join json items [String]	String
97	fn :: json array [String]	String
98	fn :: cd join json pairs loop [String String] String String String String	String
99	fn :: cd join json pairs [String String]	String
100	fn :: json object [String String]	String
101	fn :: cd quote pair vals [String String] [String String] [String String] [String String] Int	[String String]
102	fn :: json str object [String String]	String
103	fn :: cd is json ws Int	Bool
104	fn :: cd skip key sep String Int Int	Int
105	fn :: cd scan json str end String Int Int	Int
106	fn :: cd is tok delim Int	Bool
107	fn :: cd scan json tok end String Int Int	Int
108	fn :: cd extract json str vend String Int Int	String
109	fn :: cd extract json str vstart String Int	String
110	fn :: cd extract json str kpos String String Int	String
111	fn :: codec json get str String String	String
112	fn :: cd is signed int loop String Int Int	Bool
113	fn :: cd is valid int len String Int	Bool
114	fn :: cd is valid int str String	Bool
115	fn :: cd raw tok vstart String Int	String
116	fn :: cd raw tok kpos String String Int	String
117	fn :: cd raw json token String String	String
118	fn :: cd parse tok int String Int	Int
119	fn :: codec json get int String String Int	Int
120	fn :: cd parse tok bool String Bool	Bool
121	fn :: codec json get bool String String Bool	Bool

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15.3. Deep Dive into codec: Step-by-Step Examples for Every Feature

A signature table alone is never enough: let's explore every capability of the codec lib through progressive, runnable Ridgun examples. We will start with two everyday tabular recipes and then walk through every functional scenario, transformation, and boundary condition verified in src/test/ridgun/test codec.rg.

15.3.1. Example 1: Core Tabular Workflow with codec

Notice how in Ridgun the = signs and transformation steps using codec align into a clean, scannable table without unnecessary mutable variables or hidden side effects:

import codec

fn :: empaquetar parametros String String => String
      empaquetar parametros usuario redir =
        usuario base64url encode -> token_b64
        query encode [("token", token_b64), ("next", redir)]

15.3.2. Example 2: Safe Composition and Boundary Handling

Every function in the codec lib is designed to compose cleanly with boolean guards | and with the rest of the 32 libs in ridgun-libs:

import codec

fn :: construir respuesta rapida Int String => String Int
      construir respuesta rapida id nombre =
        json object [("id", json int id), ("name", json quote nombre), ("ok", json bool True)] -> doc
        json get int doc "id" 0 -> leido
        (doc, leido)

15.3.3. Example 3: RFC 4648 Hexadecimal, Standard Base64, and URL-Safe Base64url Encoding & Decoding

In this hands-on walkthrough we thoroughly exercise how codec behaves across this functional area, covering standard inputs, parameter combinations, and corner cases:

fn :: test rfc4648 hex and base64 => ()
      test rfc4648 hex and base64 =
        -- 1. Hexadecimal RFC 4648 test vectors & negative validation
        assert str eq (hex encode "") "" "hex_encode empty"
        assert str eq (hex encode "foobar") "666f6f626172" "hex_encode foobar"
        assert str eq (hex decode "666f6f626172") "foobar" "hex_decode lowercase"
        assert str eq (hex decode "666F6F626172") "foobar" "hex_decode uppercase"
        assert true (is valid hex "deadBEEF09") "is_valid_hex valid"
        assert false (is valid hex "abc") "is_valid_hex odd length"
        assert false (is valid hex "deadZZ") "is_valid_hex invalid chars"
        assert str eq (hex decode "abc") "" "hex_decode odd -> empty"

        -- 2. Base64 & Base64url RFC 4648 test vectors
        assert str eq (base64 encode "") "" "b64 empty"
        assert str eq (base64 encode "f") "Zg==" "b64 f"
        assert str eq (base64 encode "fo") "Zm8=" "b64 fo"
        assert str eq (base64 encode "foo") "Zm9v" "b64 foo"
        assert str eq (base64 encode "foob") "Zm9vYg==" "b64 foob"
        assert str eq (base64 encode "fooba") "Zm9vYmE=" "b64 fooba"
        assert str eq (base64 encode "foobar") "Zm9vYmFy" "b64 foobar"
        assert str eq (base64 decode "Zg==") "f" "b64 dec f"
        assert str eq (base64 decode "Zm8=") "fo" "b64 dec fo"
        assert str eq (base64 decode "Zm9v") "foo" "b64 dec foo"
        assert str eq (base64 decode "Zm9vYg==") "foob" "b64 dec foob"
        assert str eq (base64 decode "Zm9vYmE=") "fooba" "b64 dec fooba"
        assert str eq (base64 decode "Zm9vYmFy") "foobar" "b64 dec foobar"
        assert str eq (base64url encode "foob") "Zm9vYg" "b64url nopad"
        assert str eq (base64url decode "Zm9vYg") "foob" "b64url dec"
        assert false (is valid base64 "A") "invalid base64 len%4==1"
        assert false (is valid base64 "Zm$v") "invalid base64 char"
        assert str eq (base64 decode "Zm$v") "" "invalid base64 -> empty"

        -- 3. LIB-8: Binary-safe decoding for raw octets >= 0x80 and 0x00
        raw4 = hex decode "c800ff41"
        assert int equals (str len raw4) 4 "str_len (hex_decode c800ff41) == 4"
        assert int equals (str char at raw4 0) 200 "raw4[0] == 0xc8"
        assert int equals (str char at raw4 1) 0 "raw4[1] == 0x00"
        assert int equals (str char at raw4 2) 255 "raw4[2] == 0xff"
        assert int equals (str char at raw4 3) 65 "raw4[3] == 0x41"
        assert str eq (hex encode raw4) "c800ff41" "hex_encode raw4 == c800ff41"
        check binary roundtrip loop 10 -> ()
        ()

15.3.4. Example 4: RFC 3986 Percent-Encoding (url encode, url decode) and Query Strings (query encode, query get)

In this hands-on walkthrough we thoroughly exercise how codec behaves across this functional area, covering standard inputs, parameter combinations, and corner cases:

fn :: test rfc3986 url and query strings => ()
      test rfc3986 url and query strings =
        raw = "hello world&x=1+2%"
        enc = url encode raw
        assert str eq enc "hello%20world%26x%3D1%2B2%25" "url_encode"
        assert str eq (url decode enc) raw "url_decode roundtrip"
        assert str eq (url decode "a+b%20c") "a b c" "url_decode plus as space"
        qs  = query string encode [("q", "ridgun libs"), ("page", "2")]
        assert str eq qs "q=ridgun%20libs&page=2" "query_string_encode"
        dec = query string decode ("?" + qs)
        assert eq dec [("q", "ridgun libs"), ("page", "2")]
        ()

15.3.5. Example 5: RFC 8259 Lightweight JSON Escaping & Field Extraction (json escape, json unescape, json encode kv, json get str/int/bool)

In this hands-on walkthrough we thoroughly exercise how codec behaves across this functional area, covering standard inputs, parameter combinations, and corner cases:

fn :: test rfc8259 lightweight json => ()
      test rfc8259 lightweight json =
        esc = json escape "line1\n\"quoted\"\\tab\t"
        assert str eq esc "line1\\n\\\"quoted\\\"\\\\tab\\t" "json_escape"
        assert str eq (json unescape esc) "line1\n\"quoted\"\\tab\t" "json_unescape"
        doc = json object [("service", json quote "solstice"), ("port", json int 8443), ("tls", json bool True), ("extra", json null)]
        assert str eq doc "{\"service\":\"solstice\",\"port\":8443,\"tls\":true,\"extra\":null}" "json_object"
        assert str eq (json get str doc "service") "solstice" "json_get_str"
        assert str eq (json get str doc "missing") "" "json_get_str missing"
        assert int equals (json get int doc "port" 80) 8443 "json_get_int"
        assert int equals (json get int doc "missing" 80) 80 "json_get_int fallback"
        assert int equals (json get int doc "service" 80) 80 "json_get_int non-int fallback"
        assert true (json get bool doc "tls" False) "json_get_bool"
        assert false (json get bool doc "missing" False) "json_get_bool fallback"
        arr = json array [json int 1, json int 2, json quote "three"]
        assert str eq arr "[1,2,\"three\"]" "json_array"
        s_o = json str object [("k1", "v1"), ("k2", "v\"2")]
        assert str eq (json get str s_o "k2") "v\"2" "json_str_object escaped roundtrip"
        ()

---

15.4. Under the Hood: How codec Is Built in Pure Ridgun (src/main/ridgun/lib/codec.rg)

One of the biggest advantages of ridgun-libs is that there are no C black boxes. You can open src/main/ridgun/lib/codec.rg and read exactly how every operation is implemented using pattern matching, | / |. guard trees, and tail-call optimization (TCO). Let's inspect the key building blocks of its real implementation:

15.4.1. Internal Implementation: RFC 4648 Hexadecimal Encoding & Decoding

Observe how codec.rg declares explicit fn :: ... => ... contracts first and resolves each case through aligned equations and tail calls:

module :: codec

fn :: cd hex val Int => Int
      cd hex val c   =
        | c >= 48 and c <= 57  = c - 48
        | c >= 65 and c <= 70  = (c - 65) + 10
        | c >= 97 and c <= 102 = (c - 97) + 10
        | otherwise            = 0 - 1

fn :: cd valid hex loop String Int Int => Bool
      cd valid hex loop s idx len =
        | idx >= len                           = True
        | (cd hex val (str char at s idx)) < 0 = False
        | otherwise                            = cd valid hex loop s (idx + 1) len

fn :: cd is valid hex len String Int => Bool
      cd is valid hex len s n =
        | (n % 2) != 0 = False
        | otherwise    = cd valid hex loop s 0 n

fn :: is valid hex String => Bool
      is valid hex s      =  cd is valid hex len s (str len s)

fn :: cd hex enc byte Int => String
      cd hex enc byte b   =
        ub  = ((b % 256) + 256) % 256
        hi  = ub / 16
        lo  = ub % 16
        tbl = "0123456789abcdef"
        (str slice tbl hi (hi + 1)) + (str slice tbl lo (lo + 1))

fn :: cd hex enc loop String Int Int String String String String => String
      cd hex enc loop s idx len c0 c1 c2 c3 =
        | idx >= len = cd sb finish c0 c1 c2 c3
        | otherwise  =
          n0, n1, n2, n3 = cd sb append (cd hex enc byte (str char at s idx)) c0 c1 c2 c3
          cd hex enc loop s (idx + 1) len n0 n1 n2 n3

fn :: hex encode String => String
      hex encode s      =  cd hex enc loop s 0 (str len s) "" "" "" ""

fn :: cd hex dec loop String Int Int String String String String => String
      cd hex dec loop s idx len c0 c1 c2 c3 =
        | idx >= len = cd sb finish c0 c1 c2 c3
        | otherwise =
          hi = cd hex val (str char at s idx)
          lo = cd hex val (str char at s (idx + 1))
          b  = cd raw byte ub ((hi * 16) + lo)
          n0, n1, n2, n3 = cd sb append b c0 c1 c2 c3
          cd hex dec loop s (idx + 2) len n0 n1 n2 n3

fn :: hex decode String => String
      hex decode s      =
        | not (is valid hex s) = ""
        | otherwise            = cd hex dec loop s 0 (str len s) "" "" "" ""

15.4.2. Internal Implementation: RFC 4648 Standard Base64 & URL-Safe Base64url

Observe how codec.rg declares explicit fn :: ... => ... contracts first and resolves each case through aligned equations and tail calls:

fn :: cd b64 char String Int => String
      cd b64 char tbl    idx =
        i = idx % 64
        str slice tbl i (i + 1)

fn :: cd b64 pad suffix String Bool => String
      cd b64 pad suffix suffix True = suffix
      cd b64 pad suffix _ False = ""

fn :: cd b64 enc step String Int String Bool Int String String String String => String
      cd b64 enc step s idx tbl pad rem c0 c1 c2 c3 =
        | rem <= 0 = cd sb finish c0 c1 c2 c3
        | rem == 1 =
          b0   = str char at s idx
          out2 = (cd b64 char tbl (b0 / 4)) + (cd b64 char tbl ((b0 % 4) * 16)) + (cd b64 pad suffix "==" pad)
          cd sb finish (c0 + out2) c1 c2 c3
        | rem == 2 =
          b0   = str char at s idx
          b1   = str char at s (idx + 1)
          n    = (b0 * 256) + b1
          out3 = (cd b64 char tbl (n / 1024)) + (cd b64 char tbl ((n / 16) % 64)) + (cd b64 char tbl ((n % 16) * 4)) + (cd b64 pad suffix "=" pad)
          cd sb finish (c0 + out3) c1 c2 c3
        | otherwise =
          b0   = str char at s idx
          b1   = str char at s (idx + 1)
          b2   = str char at s (idx + 2)
          n    = (b0 * 65536) + (b1 * 256) + b2
          out4 = (cd b64 char tbl (n / 262144)) + (cd b64 char tbl ((n / 4096) % 64)) + (cd b64 char tbl ((n / 64) % 64)) + (cd b64 char tbl (n % 64))
          n0, n1, n2, n3 = cd sb append out4 c0 c1 c2 c3
          cd b64 enc step s (idx + 3) tbl pad (rem - 3) n0 n1 n2 n3

fn :: cd b64 enc rem String Int String Bool => String
      cd b64 enc rem s idx tbl pad = cd b64 enc step s idx tbl pad ((str len s) - idx) "" "" "" ""

fn :: base64 encode String => String
      base64 encode s      =  cd b64 enc rem s 0 (cd b64 lut 0) True

fn :: base64url encode String => String
      base64url encode s      =  cd b64 enc rem s 0 (cd b64url lut 0) False

fn :: cd b64 val Int => Int
      cd b64 val c   =
        | c >= 65 and c <= 90  = c - 65
        | c >= 97 and c <= 122 = (c - 97) + 26
        | c >= 48 and c <= 57  = (c - 48) + 52
        | c == 43 or c == 45   = 62
        | c == 47 or c == 95   = 63
        | otherwise            = 0 - 1

fn :: cd strip one b64 pad String Int => String
      cd strip one b64 pad s n =
        | n <= 0                        = ""
        | (str char at s (n - 1)) == 61 = str slice s 0 (n - 1)
        | otherwise                     = s

fn :: cd strip b64 pad String Int => String
      cd strip b64 pad s n =
        | (n % 4) != 0 = s
        | otherwise =
          s1 = cd strip one b64 pad s n
          cd strip one b64 pad s1 (str len s1)

fn :: cd valid b64 body String Int Int => Bool
      cd valid b64 body s idx len =
        | idx >= len                           = True
        | (cd b64 val (str char at s idx)) < 0 = False
        | otherwise                            = cd valid b64 body s (idx + 1) len

fn :: cd valid b64 raw String Int => Bool
      cd valid b64 raw raw n =
        | (n % 4) == 1 = False
        | otherwise    = cd valid b64 body raw 0 n

fn :: is valid base64 String => Bool
      is valid base64 s      =
        cd strip b64 pad s (str len s) -> raw
        cd valid b64 raw raw (str len raw)

fn :: cd b64 dec step String Int Int Int String String String String => String
      cd b64 dec step s idx len rem c0 c1 c2 c3 =
        | rem <= 1 = cd sb finish c0 c1 c2 c3
        | rem == 2 =
          v0 = cd b64 val (str char at s idx)
          v1 = cd b64 val (str char at s (idx + 1))
          b0 = cd raw byte ub (((v0 * 4) + (v1 / 16)) % 256)
          cd sb finish (c0 + b0) c1 c2 c3
        | rem == 3 =
          v0 = cd b64 val (str char at s idx)
          v1 = cd b64 val (str char at s (idx + 1))
          v2 = cd b64 val (str char at s (idx + 2))
          n  = (v0 * 1024) + (v1 * 16) + (v2 / 4)
          b01 = (cd raw byte ub ((n / 256) % 256)) + (cd raw byte ub (n % 256))
          cd sb finish (c0 + b01) c1 c2 c3
        | otherwise =
          v0 = cd b64 val (str char at s idx)
          v1 = cd b64 val (str char at s (idx + 1))
          v2 = cd b64 val (str char at s (idx + 2))
          v3 = cd b64 val (str char at s (idx + 3))
          n  = (v0 * 262144) + (v1 * 4096) + (v2 * 64) + v3
          b0 = (n / 65536) % 256
          b1 = (n / 256) % 256
          b2 = n % 256
          chunk = (cd raw byte ub b0) + (cd raw byte ub b1) + (cd raw byte ub b2)
          n0, n1, n2, n3 = cd sb append chunk c0 c1 c2 c3
          cd b64 dec step s (idx + 4) len (rem - 4) n0 n1 n2 n3

fn :: cd b64 dec loop String Int Int => String
      cd b64 dec loop s idx len = cd b64 dec step s idx len (len - idx) "" "" "" ""

fn :: base64 decode String => String
      base64 decode s      =
        | not (is valid base64 s) = ""
        | otherwise =
          raw = cd strip b64 pad s (str len s)
          cd b64 dec loop raw 0 (str len raw)

fn :: base64url decode String => String
      base64url decode s      =  base64 decode s

15.4.3. Internal Implementation: RFC 3986 URL Percent-Encoding & Query Strings

Observe how codec.rg declares explicit fn :: ... => ... contracts first and resolves each case through aligned equations and tail calls:

fn :: cd is unreserved Int => Bool
      cd is unreserved c   =
        | c >= 65 and c <= 90                        = True
        | c >= 97 and c <= 122                       = True
        | c >= 48 and c <= 57                        = True
        | c == 45 or c == 95 or c == 46 or c == 126  = True
        | otherwise                                  = False

fn :: cd scan unres String String Int Int => Int
      cd scan unres s umap idx len =
        | idx >= len = len
        | (str char at umap ((str char at s idx) % 256)) == 49 =
          cd scan unres s umap (idx + 1) len
        | otherwise = idx

fn :: cd pct byte lut String Int => String
      cd pct byte lut lut b =
        ub = ((b % 256) + 256) % 256
        hi = ub / 16
        lo = ub % 16
        "%" + (str slice lut hi (hi + 1)) + (str slice lut lo (lo + 1))

fn :: cd url enc step String String String Int Int Int String String String String => String
      cd url enc step s umap lut run_start next_idx len c0 c1 c2 c3 =
        | next_idx >= len =
          | run_start == 0 = s
          | otherwise      = cd sb finish (c0 + (str slice s run_start len)) c1 c2 c3 |.
        | otherwise =
          piece = (str slice s run_start next_idx) + (cd pct byte lut lut (str char at s next_idx))
          n0, n1, n2, n3 = cd sb append piece c0 c1 c2 c3
          cd url enc loop s umap lut (next_idx + 1) len n0 n1 n2 n3

fn :: cd url enc loop String String String Int Int String String String String => String
      cd url enc loop s umap lut run_start len c0 c1 c2 c3 =
        | run_start >= len = cd sb finish c0 c1 c2 c3
        | otherwise        = cd url enc step s umap lut run_start (cd scan unres s umap run_start len) len c0 c1 c2 c3

fn :: url encode String => String
      url encode s      =
        umap = "0000000000000000000000000000000000000000000001101111111111000000011111111111111111111111111000010111111111111111111111111110001000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
        cd url enc loop s umap "0123456789ABCDEF" 0 (str len s) "" "" "" ""

fn :: cd scan url plain String Int Int => Int
      cd scan url plain s idx len =
        | idx >= len = len
        | (str char at s idx) == 37 or (str char at s idx) == 43 = idx
        | otherwise = cd scan url plain s (idx + 1) len

fn :: cd url dec pct String Int Int Int Int String String String String String => String
      cd url dec pct s next_idx len hi lo prefix c0 c1 c2 c3 =
        | hi >= 0 and lo >= 0 =
          piece = prefix + (cd raw byte ub ((hi * 16) + lo))
          n0, n1, n2, n3 = cd sb append piece c0 c1 c2 c3
          cd url dec loop s (next_idx + 3) len n0 n1 n2 n3
        | otherwise =
          piece = prefix + "%"
          n0, n1, n2, n3 = cd sb append piece c0 c1 c2 c3
          cd url dec loop s (next_idx + 1) len n0 n1 n2 n3

fn :: cd url dec step String Int Int Int String String String String => String
      cd url dec step s run_start next_idx len c0 c1 c2 c3 =
        | next_idx >= len =
          | run_start == 0 = s
          | otherwise      = cd sb finish (c0 + (cd byte slice s run_start len)) c1 c2 c3 |.
        | (str char at s next_idx) == 43 =
          piece = (cd byte slice s run_start next_idx) + " "
          n0, n1, n2, n3 = cd sb append piece c0 c1 c2 c3
          cd url dec loop s (next_idx + 1) len n0 n1 n2 n3
        | (next_idx + 2) < len =
          prefix = cd byte slice s run_start next_idx
          hi = cd hex val (str char at s (next_idx + 1))
          lo = cd hex val (str char at s (next_idx + 2))
          cd url dec pct s next_idx len hi lo prefix c0 c1 c2 c3
        | otherwise =
          piece = (cd byte slice s run_start next_idx) + "%"
          n0, n1, n2, n3 = cd sb append piece c0 c1 c2 c3
          cd url dec loop s (next_idx + 1) len n0 n1 n2 n3

fn :: cd url dec loop String Int Int String String String String => String
      cd url dec loop s run_start len c0 c1 c2 c3 =
        | run_start >= len = cd sb finish c0 c1 c2 c3
        | otherwise        = cd url dec step s run_start (cd scan url plain s run_start len) len c0 c1 c2 c3

fn :: url decode String => String
      url decode s      =  cd url dec loop s 0 (str len s) "" "" "" ""

fn :: cd pair key (String String) => String
      cd pair key (k, _)          =  k

fn :: cd pair val (String String) => String
      cd pair val (_, v)          =  v

fn :: cd qs enc loop [String String] String String String String => String
      cd qs enc loop []          c0 c1 c2 c3 =  cd sb finish c0 c1 c2 c3
      cd qs enc loop (pair:rest) c0 c1 c2 c3 =
        piece = "&" + (url encode (cd pair key pair)) + "=" + (url encode (cd pair val pair))
        n0, n1, n2, n3 = cd sb append piece c0 c1 c2 c3
        cd qs enc loop rest n0 n1 n2 n3

fn :: query string encode [String String] => String
      query string encode []              =  ""
      query string encode (pair:rest)     =
        first = (url encode (cd pair key pair)) + "=" + (url encode (cd pair val pair))
        cd qs enc loop rest first "" "" ""

fn :: cd parse kv at String Int => String String
      cd parse kv at item eq_idx =
        | eq_idx < 0 = (url decode item, "")
        | otherwise  = (url decode (cd byte slice item 0 eq_idx), url decode (cd byte slice item (eq_idx + 1) (str len item)))

fn :: cd parse kv item String => String String
      cd parse kv item item   =  cd parse kv at item (cd index of item "=")

fn :: cd kv lb append2 [String String] [String String] Int => [String String] [String String] [String String] Int
      cd kv lb append2 n1 l2 cnt =
        | (cnt % 1024) == 0 = ([], [], l2 :: n1, cnt)
        | otherwise         = ([], n1, l2, cnt)

fn :: cd kv lb append1 [String String] [String String] [String String] Int => [String String] [String String] [String String] Int
      cd kv lb append1 n0 l1 l2 cnt =
        | (cnt % 32) == 0 = cd kv lb append2 (l1 :: n0) l2 cnt
        | otherwise       = (n0, l1, l2, cnt)

fn :: cd kv lb append (String String) [String String] [String String] [String String] Int => [String String] [String String] [String String] Int
      cd kv lb append item l0 l1 l2 cnt =
        cd kv lb append1 (l0 :: [item]) l1 l2 (cnt + 1)

fn :: cd parse qs list [String] [String String] [String String] [String String] Int => [String String]
      cd parse qs list []       l0 l1 l2 _   =  l2 :: (l1 :: l0)
      cd parse qs list (x:rest) l0 l1 l2 cnt =
        | (str len x) == 0 = cd parse qs list rest l0 l1 l2 cnt
        | otherwise        =
          n0, n1, n2, ncnt = cd kv lb append (cd parse kv item x) l0 l1 l2 cnt
          cd parse qs list rest n0 n1 n2 ncnt

fn :: cd strip leading q String => String
      cd strip leading q qs     =
        | str starts with qs "?" = str slice qs 1 (str len qs)
        | otherwise              = qs

fn :: cd decode clean qs String => [String String]
      cd decode clean qs clean  =
        | (str len clean) == 0 = []
        | otherwise            = cd parse qs list (cd split char loop clean "&" 38 0 0 (str len clean) [] [] [] 0) [] [] [] 0

fn :: query string decode String => [String String]
      query string decode qs     =  cd decode clean qs (cd strip leading q qs)

15.4.4. Internal Implementation: RFC 8259 Lightweight JSON Formatting & Field Extraction

Observe how codec.rg declares explicit fn :: ... => ... contracts first and resolves each case through aligned equations and tail calls:

fn :: cd is json esc Int => Bool
      cd is json esc c =
        ub = ((c % 256) + 256) % 256
        ub < 32 or ub == 34 or ub == 92

fn :: cd scan json plain String Int Int => Int
      cd scan json plain s idx len =
        | idx >= len = len
        | cd is json esc (str char at s idx) = idx
        | otherwise = cd scan json plain s (idx + 1) len

fn :: cd json esc hex2 Int => String
      cd json esc hex2 ub =
        hi  = (ub / 16) % 16
        lo  = ub % 16
        tbl = "0123456789abcdef"
        "\\u00" + (str slice tbl hi (hi + 1)) + (str slice tbl lo (lo + 1))

fn :: cd json esc code ub Int => String
      cd json esc code ub ub =
        | ub == 34  = "\\\""
        | ub == 92  = "\\\\"
        | ub == 8   = "\\b"
        | ub == 12  = "\\f"
        | ub == 10  = "\\n"
        | ub == 13  = "\\r"
        | ub == 9   = "\\t"
        | otherwise = cd json esc hex2 ub

fn :: cd json esc code Int => String
      cd json esc code c =
        cd json esc code ub (((c % 256) + 256) % 256)

fn :: cd json esc step String Int Int Int String String String String => String
      cd json esc step s idx next_idx len c0 c1 c2 c3 =
        | next_idx >= len =
          | idx == 0  = s
          | otherwise = cd sb finish (c0 + (cd byte slice s idx len)) c1 c2 c3 |.
        | otherwise =
          piece = (cd byte slice s idx next_idx) + (cd json esc code (str char at s next_idx))
          n0, n1, n2, n3 = cd sb append piece c0 c1 c2 c3
          cd json esc loop s (next_idx + 1) len n0 n1 n2 n3

fn :: cd json esc loop String Int Int String String String String => String
      cd json esc loop s idx len c0 c1 c2 c3 =
        | idx >= len = cd sb finish c0 c1 c2 c3
        | otherwise  = cd json esc step s idx (cd scan json plain s idx len) len c0 c1 c2 c3

fn :: json escape String => String
      json escape s      =  cd json esc loop s 0 (str len s) "" "" "" ""

fn :: cd json unesc char String Int Int => String
      cd json unesc char s idx nc =
        | nc == 34  = "\""
        | nc == 92  = "\\"
        | nc == 47  = "/"
        | nc == 98  = char from code 8
        | nc == 102 = char from code 12
        | nc == 110 = "\n"
        | nc == 114 = "\r"
        | nc == 116 = "\t"
        | otherwise = str slice s (idx + 1) (idx + 2)

fn :: cd scan no backslash String Int Int => Int
      cd scan no backslash s idx len =
        | idx >= len = len
        | (str char at s idx) == 92 = idx
        | otherwise = cd scan no backslash s (idx + 1) len

fn :: cd json unesc cp Int Int => String Int
      cd json unesc cp next_idx cp =
        | cp <= 255 = (cd raw byte ub cp, next_idx + 6)
        | otherwise = (char from code cp, next_idx + 6)

fn :: cd json unesc u4 Int Int Int Int Int => String Int
      cd json unesc u4 next_idx d0 d1 d2 d3 =
        | d0 < 0 or d1 < 0 or d2 < 0 or d3 < 0 = ("\\u", next_idx + 2)
        | otherwise = cd json unesc cp next_idx ((((d0 * 16) + d1) * 256) + (d2 * 16) + d3)

fn :: cd json unesc step String Int Int Int String String String String => String
      cd json unesc step s idx next_idx len c0 c1 c2 c3 =
        | next_idx >= len =
          | idx == 0  = s
          | otherwise = cd sb finish (c0 + (cd byte slice s idx len)) c1 c2 c3 |.
        | (next_idx + 5) < len and (str char at s (next_idx + 1)) == 117 =
          d0 = cd hex val (str char at s (next_idx + 2))
          d1 = cd hex val (str char at s (next_idx + 3))
          d2 = cd hex val (str char at s (next_idx + 4))
          d3 = cd hex val (str char at s (next_idx + 5))
          rep, adv = cd json unesc u4 next_idx d0 d1 d2 d3
          piece = (cd byte slice s idx next_idx) + rep
          n0, n1, n2, n3 = cd sb append piece c0 c1 c2 c3
          cd json unesc loop s adv len n0 n1 n2 n3
        | (next_idx + 1) < len =
          piece = (cd byte slice s idx next_idx) + (cd json unesc char s next_idx (str char at s (next_idx + 1)))
          n0, n1, n2, n3 = cd sb append piece c0 c1 c2 c3
          cd json unesc loop s (next_idx + 2) len n0 n1 n2 n3
        | otherwise =
          cd sb finish (c0 + (cd byte slice s idx len)) c1 c2 c3

fn :: cd json unesc loop String Int Int String String String String => String
      cd json unesc loop s idx len c0 c1 c2 c3 =
        | idx >= len = cd sb finish c0 c1 c2 c3
        | otherwise  = cd json unesc step s idx (cd scan no backslash s idx len) len c0 c1 c2 c3

fn :: json unescape String => String
      json unescape s      =
        | not (str contains s "\\") = s
        | otherwise                 = cd json unesc loop s 0 (str len s) "" "" "" ""

fn :: json quote String => String
      json quote s      =  "\"" + (json escape s) + "\""

fn :: json int Int => String
      json int n   =  int to str n

fn :: json bool Bool  => String
      json bool True  =  "true"
      json bool False =  "false"

fn :: json null => String
      json null =  "null"

fn :: cd join json loop [String] String String String String => String
      cd join json loop []       c0 c1 c2 c3 =  cd sb finish c0 c1 c2 c3
      cd join json loop (x:rest) c0 c1 c2 c3 =
        n0, n1, n2, n3 = cd sb append ("," + x) c0 c1 c2 c3
        cd join json loop rest n0 n1 n2 n3

fn :: cd join json items [String] => String
      cd join json items []       =  ""
      cd join json items (x:rest) =  cd join json loop rest x "" "" ""

fn :: json array [String] => String
      json array items    =  "[" + (cd join json items items) + "]"

fn :: cd join json pairs loop [String String] String String String String => String
      cd join json pairs loop []          c0 c1 c2 c3 =  cd sb finish c0 c1 c2 c3
      cd join json pairs loop (pair:rest) c0 c1 c2 c3 =
        piece = "," + (json quote (cd pair key pair)) + ":" + (cd pair val pair)
        n0, n1, n2, n3 = cd sb append piece c0 c1 c2 c3
        cd join json pairs loop rest n0 n1 n2 n3

fn :: cd join json pairs [String String] => String
      cd join json pairs []              =  ""
      cd join json pairs (pair:rest)     =
        first = (json quote (cd pair key pair)) + ":" + (cd pair val pair)
        cd join json pairs loop rest first "" "" ""

fn :: json object [String String] => String
      json object pairs           =  "{" + (cd join json pairs pairs) + "}"

fn :: cd quote pair vals [String String] [String String] [String String] [String String] Int => [String String]
      cd quote pair vals []          l0 l1 l2 _   =  l2 :: (l1 :: l0)
      cd quote pair vals (pair:rest) l0 l1 l2 cnt =
        n0, n1, n2, ncnt = cd kv lb append (cd pair key pair, json quote (cd pair val pair)) l0 l1 l2 cnt
        cd quote pair vals rest n0 n1 n2 ncnt

fn :: json str object [String String] => String
      json str object pairs           =  json object (cd quote pair vals pairs [] [] [] 0)

fn :: cd is json ws Int => Bool
      cd is json ws c   =  c == 32 or c == 9 or c == 10 or c == 13 or c == 58

fn :: cd skip key sep String Int Int => Int
      cd skip key sep s idx len =
        | idx >= len                        = idx
        | cd is json ws (str char at s idx) = cd skip key sep s (idx + 1) len
        | otherwise                         = idx

fn :: cd scan json str end String Int Int => Int
      cd scan json str end s idx len =
        | idx >= len                = 0 - 1
        | (str char at s idx) == 92 = cd scan json str end s (idx + 2) len
        | (str char at s idx) == 34 = idx
        | otherwise                 = cd scan json str end s (idx + 1) len

fn :: cd is tok delim Int => Bool
      cd is tok delim c   =  c == 44 or c == 125 or c == 93 or c == 32 or c == 9 or c == 10 or c == 13

fn :: cd scan json tok end String Int Int => Int
      cd scan json tok end s idx len =
        | idx >= len                           = len
        | cd is tok delim (str char at s idx)  = idx
        | otherwise                            = cd scan json tok end s (idx + 1) len

fn :: cd extract json str vend String Int Int => String
      cd extract json str vend doc vstart vend =
        | vend < 0  = ""
        | otherwise = json unescape (str slice doc (vstart + 1) vend)

fn :: cd extract json str vstart String Int => String
      cd extract json str vstart doc vstart =
        | vstart >= (str len doc)        = ""
        | (str char at doc vstart) != 34 = ""
        | otherwise                      = cd extract json str vend doc vstart (cd scan json str end doc (vstart + 1) (str len doc))

fn :: cd extract json str kpos String String Int => String
      cd extract json str kpos doc pat kpos =
        | kpos < 0  = ""
        | otherwise = cd extract json str vstart doc (cd skip key sep doc (kpos + (str len pat)) (str len doc))

fn :: codec json get str String String => String
      codec json get str doc    key    =
        pat = "\"" + (json escape key) + "\""
        cd extract json str kpos doc pat (cd index of doc pat)

fn :: cd is signed int loop String Int Int => Bool
      cd is signed int loop s idx len =
        | idx >= len                                           = True
        | (str char at s idx) < 48 or (str char at s idx) > 57 = False
        | otherwise                                            = cd is signed int loop s (idx + 1) len

fn :: cd is valid int len String Int => Bool
      cd is valid int len s n =
        | n == 0                  = False
        | (str char at s 0) == 45 =
          | n <= 1    = False
          | otherwise = cd is signed int loop s 1 n |.
        | otherwise               = cd is signed int loop s 0 n

fn :: cd is valid int str String => Bool
      cd is valid int str s = cd is valid int len s (str len s)

fn :: cd raw tok vstart String Int => String
      cd raw tok vstart doc vstart =
        | vstart >= (str len doc) = ""
        | otherwise =
          vend = cd scan json tok end doc vstart (str len doc)
          str slice doc vstart vend

fn :: cd raw tok kpos String String Int => String
      cd raw tok kpos doc pat kpos =
        | kpos < 0  = ""
        | otherwise = cd raw tok vstart doc (cd skip key sep doc (kpos + (str len pat)) (str len doc))

fn :: cd raw json token String String => String
      cd raw json token doc key =
        pat = "\"" + (json escape key) + "\""
        cd raw tok kpos doc pat (cd index of doc pat)

fn :: cd parse tok int String Int => Int
      cd parse tok int tok fallback =
        | not (cd is valid int str tok) = fallback
        | otherwise                     = str to int tok

fn :: codec json get int String String Int => Int
      codec json get int doc key fallback = cd parse tok int (cd raw json token doc key) fallback

fn :: cd parse tok bool String Bool => Bool
      cd parse tok bool tok fallback =
        | tok == "true"  = True
        | tok == "false" = False
        | otherwise      = fallback

fn :: codec json get bool String String Bool => Bool
      codec json get bool doc key fallback = cd parse tok bool (cd raw json token doc key) fallback

---

15.5. Algorithmic Guarantees, RMM1/RMM2 Memory, and the 5 Golden Rules of codec

• Algorithmic & Safety Guarantee: Deterministic rejection of malformed Hex or Base64 inputs (returning "" with zero out-of-bounds reads) and exact $decode(encode(x)) == x$ round-trip fidelity.
• $O(1)$ Stack Complexity via TCO: Every recursive loop in src/main/ridgun/lib/codec.rg is in tail position, so ridgunc compiles them into native jumps with zero stack growth.
• Deterministic Memory (RMM1/RMM2): Zero garbage-collector pauses; all intermediate allocations are reclaimed deterministically on scope exit.
• Continuous Verification: Statically checked via stable check and tested by the automated suite in src/test/ridgun/test codec.rg.

The 5 Golden Rules When Programming with codec

1. Declare import codec at the top of your file and take advantage of space/underscore equivalence so your code reads like natural prose.
2. Align your data pipelines with =: chain codec calls into named intermediate steps and let stable format align the columns.
3. Leverage codec's total functions inside | guards: inspect return values or unwrap ADTs via pattern matching rather than assuming external input is valid.
4. Avoid cloning large structures when only reading: remember that under RMM2, function input arguments incur zero reference-count overhead (+0 / -0).
5. Pair codec with test (import test): always lock in your domain invariants with assert equals or assert true.

---

In Chapter 16, we will explore the json lib in full depth (The json Lib — Recursive RFC 8259 AST Parser, Pretty-Printer, and Dot-Path Queries).