From 6de2d68a700a137bbe55668e036c62280ece8bb5 Mon Sep 17 00:00:00 2001
From: Bruce Hill <bruce@bruce-hill.com>
Date: Tue, 1 Apr 2025 16:55:24 -0400
Subject: [PATCH] Moved RNG out of the compiler and into a standalone library

---
 docs/README.md                           |   1 -
 examples/core/core.tm                    |   1 +
 docs/rng.md => examples/random/README.md |  37 +--
 {src/stdlib => examples/random}/chacha.h |  31 ++-
 examples/random/random.tm                | 240 ++++++++++++++++++++
 examples/random/sysrandom.h              |  14 ++
 src/compile.c                            |  38 ++--
 src/environment.c                        |  20 --
 src/environment.h                        |   1 -
 src/parse.c                              |  24 +-
 src/parse.h                              |   1 +
 src/stdlib/arrays.c                      |  71 ++++--
 src/stdlib/arrays.h                      |  10 +-
 src/stdlib/datatypes.h                   |   2 -
 src/stdlib/rng.c                         | 274 -----------------------
 src/stdlib/rng.h                         |  36 ---
 src/stdlib/stdlib.c                      |   6 -
 src/stdlib/tomo.h                        |   1 -
 test/arrays.tm                           |   6 +-
 test/integers.tm                         |  12 +-
 test/rng.tm                              |  40 ----
 21 files changed, 387 insertions(+), 479 deletions(-)
 rename docs/rng.md => examples/random/README.md (84%)
 rename {src/stdlib => examples/random}/chacha.h (87%)
 create mode 100644 examples/random/random.tm
 create mode 100644 examples/random/sysrandom.h
 delete mode 100644 src/stdlib/rng.c
 delete mode 100644 src/stdlib/rng.h
 delete mode 100644 test/rng.tm

diff --git a/docs/README.md b/docs/README.md
index f788432..ff79503 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -26,7 +26,6 @@ Information about Tomo's built-in types can be found here:
 - [Integers](integers.md)
 - [Languages](langs.md)
 - [Paths](paths.md)
-- [Random Number Generators](rng.md)
 - [Sets](sets.md)
 - [Structs](structs.md)
 - [Tables](tables.md)
diff --git a/examples/core/core.tm b/examples/core/core.tm
index b49448d..f7259b7 100644
--- a/examples/core/core.tm
+++ b/examples/core/core.tm
@@ -7,3 +7,4 @@ use shell
 use colorful
 use log
 use pthreads
+use random
diff --git a/docs/rng.md b/examples/random/README.md
similarity index 84%
rename from docs/rng.md
rename to examples/random/README.md
index 90c7536..697f3f7 100644
--- a/docs/rng.md
+++ b/examples/random/README.md
@@ -1,9 +1,9 @@
 # Random Number Generators (RNG)
 
-Tomo comes with an `RNG` type (Random Number Generator). This type represents a
-self-contained piece of data that encapsulates the state of a relatively fast
-and relatively secure pseudo-random number generator. The current
-implementation is based on the [ChaCha20 stream
+This library provides an `RNG` type (Random Number Generator). This type
+represents a self-contained piece of data that encapsulates the state of a
+relatively fast and relatively secure pseudo-random number generator. The
+current implementation is based on the [ChaCha20 stream
 cipher,](https://en.wikipedia.org/wiki/Salsa20#ChaCha_variant) inspired by
 [`arc4random` in OpenBSD.](https://man.openbsd.org/arc4random.3)
 
@@ -16,7 +16,7 @@ a Tomo program launches.
 ## RNG Functions
 
 This documentation provides details on RNG functions available in the API.
-[Arrays](arrays.md) also have some methods which use RNG values:
+Arrays also have some methods which use RNG values:
 `array:shuffle()`, `array:shuffled()`, `array:random()`, and `array:sample()`.
 
 - [`func bool(rng: RNG, p: Num = 0.5 -> Bool)`](#bool)
@@ -25,8 +25,9 @@ This documentation provides details on RNG functions available in the API.
 - [`func copy(rng: RNG -> RNG)`](#copy)
 - [`func int(rng: RNG, min: Int, max: Int -> Int)`](#int`, `int64`, `int32`, `int16`, `int8)
 - [`func new(seed: [Byte] = (/dev/urandom):read_bytes(40)! -> RNG)`](#new)
-- [`func num(rng: RNG, min: Num = 0.0, max: Num = 1.0 -> Int)`](#num`, `num32)
-- [`func set_seed(rng: RNG, seed: [Byte])`](#set_seed)
+- [`func num(rng: RNG, min: Num = 0.0, max: Num = 1.0 -> Num)`](#num`, `num32)
+
+-------------
 
 ### `bool`
 Generate a random boolean value with a given probability.
@@ -193,25 +194,3 @@ A floating point number uniformly chosen from the range `[min, max]`
 >> random:num(1, 10)
 = 9.512830439975572
 ```
-
----
-
-### `set_seed`
-Set the seed for an RNG.
-
-```tomo
-func set_seed(rng: RNG, seed: [Byte])
-```
-
-- `rng`: The random number generator to modify.
-- `seed`: A new seed to re-seed the random number generator with. A seed length
-  of 40 bytes is recommended. Seed lengths of less than 40 bytes are padded
-  with zeroes.
-
-**Returns:**  
-Nothing.
-
-**Example:**  
-```tomo
-random:set_seed((/dev/urandom):read_bytes(40))
-```
diff --git a/src/stdlib/chacha.h b/examples/random/chacha.h
similarity index 87%
rename from src/stdlib/chacha.h
rename to examples/random/chacha.h
index 69d79ea..7df352f 100644
--- a/src/stdlib/chacha.h
+++ b/examples/random/chacha.h
@@ -1,3 +1,4 @@
+#pragma once
 /*
 chacha-merged.c version 20080118
 D. J. Bernstein
@@ -15,6 +16,9 @@ typedef struct
   u32 input[16]; /* could be compressed */
 } chacha_ctx;
 
+#define KEYSZ 32
+#define IVSZ 8
+
 #define U8C(v) (v##U)
 #define U32C(v) (v##U)
 
@@ -50,31 +54,22 @@ typedef struct
   c = PLUS(c, d); b = ROTATE(XOR(b, c), 7);
 
 static const char sigma[16] = "expand 32-byte k";
-static const char tau[16] = "expand 16-byte k";
 
 static void
-chacha_keysetup(chacha_ctx *chacha, const u8 *k, u32 kbits)
+chacha_keysetup(chacha_ctx *chacha, const u8 *k)
 {
-  const char *constants;
-
+  chacha->input[0] = U8TO32_LITTLE(sigma + 0);
+  chacha->input[1] = U8TO32_LITTLE(sigma + 4);
+  chacha->input[2] = U8TO32_LITTLE(sigma + 8);
+  chacha->input[3] = U8TO32_LITTLE(sigma + 12);
   chacha->input[4] = U8TO32_LITTLE(k + 0);
   chacha->input[5] = U8TO32_LITTLE(k + 4);
   chacha->input[6] = U8TO32_LITTLE(k + 8);
   chacha->input[7] = U8TO32_LITTLE(k + 12);
-  if (kbits == 256) { /* recommended */
-    k += 16;
-    constants = sigma;
-  } else { /* kbits == 128 */
-    constants = tau;
-  }
-  chacha->input[8] = U8TO32_LITTLE(k + 0);
-  chacha->input[9] = U8TO32_LITTLE(k + 4);
-  chacha->input[10] = U8TO32_LITTLE(k + 8);
-  chacha->input[11] = U8TO32_LITTLE(k + 12);
-  chacha->input[0] = U8TO32_LITTLE(constants + 0);
-  chacha->input[1] = U8TO32_LITTLE(constants + 4);
-  chacha->input[2] = U8TO32_LITTLE(constants + 8);
-  chacha->input[3] = U8TO32_LITTLE(constants + 12);
+  chacha->input[8] = U8TO32_LITTLE(k + 16);
+  chacha->input[9] = U8TO32_LITTLE(k + 20);
+  chacha->input[10] = U8TO32_LITTLE(k + 24);
+  chacha->input[11] = U8TO32_LITTLE(k + 28);
 }
 
 static void
diff --git a/examples/random/random.tm b/examples/random/random.tm
new file mode 100644
index 0000000..7db0201
--- /dev/null
+++ b/examples/random/random.tm
@@ -0,0 +1,240 @@
+# Random Number Generator (RNG) implementation based on ChaCha
+
+use ./sysrandom.h
+use ./chacha.h
+
+struct chacha_ctx(j0,j1,j2,j3,j4,j5,j6,j7,j8,j9,j10,j11,j12,j13,j14,j15:Int32; extern, secret):
+    func from_seed(seed=[:Byte] -> chacha_ctx):
+        return inline C : chacha_ctx {
+            chacha_ctx ctx;
+            uint8_t seed_bytes[KEYSZ + IVSZ] = {};
+            for (int64_t i = 0; i < (int64_t)sizeof(seed_bytes); i++)
+                seed_bytes[i] = i < _$seed.length ? *(uint8_t*)(_$seed.data + i*_$seed.stride) : 0;
+            chacha_keysetup(&ctx, seed_bytes);
+            chacha_ivsetup(&ctx, seed_bytes + KEYSZ);
+            ctx;
+        }
+
+default_random := RandomNumberGenerator.new()
+
+func _os_random_bytes(count:Int64 -> [Byte]):
+    return inline C : [Byte] {
+        uint8_t *random_bytes = GC_MALLOC_ATOMIC(_$count);
+        getrandom(random_bytes, _$count, 0);
+        (Array_t){.length=_$count, .data=random_bytes, .stride=1, .atomic=1};
+    }
+
+struct RandomNumberGenerator(_chacha:chacha_ctx, _random_bytes=[:Byte]; secret):
+    func new(seed=none:[Byte], -> @RandomNumberGenerator):
+        ctx := chacha_ctx.from_seed(seed or _os_random_bytes(40))
+        return @RandomNumberGenerator(ctx, [:Byte])
+
+    func _rekey(rng:&RandomNumberGenerator):
+        rng._random_bytes = inline C : [Byte] {
+            Byte_t new_keystream[KEYSZ + IVSZ] = {};
+            // Fill the buffer with the keystream
+            chacha_encrypt_bytes(&_$rng->_chacha, new_keystream, new_keystream, sizeof(new_keystream));
+            // Immediately reinitialize for backtracking resistance
+            chacha_keysetup(&_$rng->_chacha, new_keystream);
+            chacha_ivsetup(&_$rng->_chacha, new_keystream + KEYSZ);
+            Array_t new_bytes = (Array_t){.data=GC_MALLOC_ATOMIC(1024), .length=1024, .stride=1, .atomic=1};
+            memset(new_bytes.data, 0, new_bytes.length);
+            chacha_encrypt_bytes(&_$rng->_chacha, new_bytes.data, new_bytes.data, new_bytes.length);
+            new_bytes;
+        }
+
+    func _fill_bytes(rng:&RandomNumberGenerator, dest:&Memory, needed:Int64):
+        inline C {
+            while (_$needed > 0) {
+                if (_$rng->_random_bytes.length == 0)
+                    _$random$RandomNumberGenerator$_rekey(_$rng);
+
+                assert(_$rng->_random_bytes.stride == 1);
+
+                int64_t batch_size = MIN(_$needed, _$rng->_random_bytes.length);
+                uint8_t *batch_src = _$rng->_random_bytes.data;
+                memcpy(_$dest, batch_src, batch_size);
+                memset(batch_src, 0, batch_size);
+                _$rng->_random_bytes.data += batch_size;
+                _$rng->_random_bytes.length -= batch_size;
+                _$dest += batch_size;
+                _$needed -= batch_size;
+            }
+        }
+
+    func bytes(rng:&RandomNumberGenerator, count:Int -> [Byte]):
+        return inline C : [Byte] {
+            int64_t count64 = Int64$from_int(_$count, false);
+            Array_t ret = {.data=GC_MALLOC_ATOMIC(count64), .stride=1, .atomic=1, .length=count64};
+            _$random$RandomNumberGenerator$_fill_bytes(_$rng, ret.data, count64);
+            ret;
+        }
+
+    func byte(rng:&RandomNumberGenerator -> Byte):
+        return inline C : Byte {
+            Byte_t b;
+            _$random$RandomNumberGenerator$_fill_bytes(_$rng, &b, sizeof(b));
+            b;
+        }
+
+    func bool(rng:&RandomNumberGenerator, probability=0.5 -> Bool):
+        if probability == 0.5:
+            return rng:byte() < 0x80
+        else:
+            return rng:num(0., 1.) < 0.5
+
+    func int64(rng:&RandomNumberGenerator, min=Int64.min, max=Int64.max -> Int64):
+        fail("Random minimum value $min is larger than the maximum value $max") if min > max
+        return min if min == max
+        if min == Int64.min and max == Int64.max:
+            return inline C : Int64 {
+                int64_t i;
+                _$random$RandomNumberGenerator$_fill_bytes(_$rng, &i, sizeof(i));
+                i;
+            }
+
+        return inline C : Int64 {
+            uint64_t range = (uint64_t)_$max - (uint64_t)_$min + 1;
+            uint64_t min_r = -range % range;
+            uint64_t r;
+            for (;;) {
+                _$random$RandomNumberGenerator$_fill_bytes(_$rng, (uint8_t*)&r, sizeof(r));
+                if (r >= min_r) break;
+            }
+            (int64_t)((uint64_t)_$min + (r % range));
+        }
+
+    func int32(rng:&RandomNumberGenerator, min=Int32.min, max=Int32.max -> Int32):
+        fail("Random minimum value $min is larger than the maximum value $max") if min > max
+        return min if min == max
+        if min == Int32.min and max == Int32.max:
+            return inline C : Int32 {
+                int32_t i;
+                _$random$RandomNumberGenerator$_fill_bytes(_$rng, &i, sizeof(i));
+                i;
+            }
+
+        return inline C : Int32 {
+            uint32_t range = (uint32_t)_$max - (uint32_t)_$min + 1;
+            uint32_t min_r = -range % range;
+            uint32_t r;
+            for (;;) {
+                _$random$RandomNumberGenerator$_fill_bytes(_$rng, (uint8_t*)&r, sizeof(r));
+                if (r >= min_r) break;
+            }
+            (int32_t)((uint32_t)_$min + (r % range));
+        }
+
+    func int16(rng:&RandomNumberGenerator, min=Int16.min, max=Int16.max -> Int16):
+        fail("Random minimum value $min is larger than the maximum value $max") if min > max
+        return min if min == max
+        if min == Int16.min and max == Int16.max:
+            return inline C : Int16 {
+                int16_t i;
+                _$random$RandomNumberGenerator$_fill_bytes(_$rng, &i, sizeof(i));
+                i;
+            }
+
+        return inline C : Int16 {
+            uint16_t range = (uint16_t)_$max - (uint16_t)_$min + 1;
+            uint16_t min_r = -range % range;
+            uint16_t r;
+            for (;;) {
+                _$random$RandomNumberGenerator$_fill_bytes(_$rng, (uint8_t*)&r, sizeof(r));
+                if (r >= min_r) break;
+            }
+            (int16_t)((uint16_t)_$min + (r % range));
+        }
+
+    func int8(rng:&RandomNumberGenerator, min=Int8.min, max=Int8.max -> Int8):
+        fail("Random minimum value $min is larger than the maximum value $max") if min > max
+        return min if min == max
+        if min == Int8.min and max == Int8.max:
+            return inline C : Int8 {
+                int8_t i;
+                _$random$RandomNumberGenerator$_fill_bytes(_$rng, &i, sizeof(i));
+                i;
+            }
+
+        return inline C : Int8 {
+            uint8_t range = (uint8_t)_$max - (uint8_t)_$min + 1;
+            uint8_t min_r = -range % range;
+            uint8_t r;
+            for (;;) {
+                _$random$RandomNumberGenerator$_fill_bytes(_$rng, (uint8_t*)&r, sizeof(r));
+                if (r >= min_r) break;
+            }
+            (int8_t)((uint8_t)_$min + (r % range));
+        }
+
+    func num(rng:&RandomNumberGenerator, min=0., max=1. -> Num):
+        return inline C : Num {
+            if (_$min > _$max) fail("Random minimum value (", _$min, ") is larger than the maximum value (", _$max, ")");
+            if (_$min == _$max) return _$min;
+
+            union {
+                Num_t num;
+                uint64_t bits;
+            } r = {.bits=0}, one = {.num=1.0};
+            _$random$RandomNumberGenerator$_fill_bytes(_$rng, (uint8_t*)&r, sizeof(r));
+
+            // Set r.num to 1.<random-bits>
+            r.bits &= ~(0xFFFULL << 52);
+            r.bits |= (one.bits & (0xFFFULL << 52));
+
+            r.num -= 1.0;
+
+            (_$min == 0.0 && _$max == 1.0) ? r.num : ((1.0-r.num)*_$min + r.num*_$max);
+        }
+
+    func num32(rng:&RandomNumberGenerator, min=Num32(0.), max=Num32(1.) -> Num32):
+        return Num32(rng:num(Num(min), Num(max)))
+
+    func int(rng:&RandomNumberGenerator, min:Int, max:Int -> Int):
+        return inline C : Int {
+            if (likely(((_$min.small & _$max.small) & 1) != 0)) {
+                int32_t r = _$random$RandomNumberGenerator$int32(_$rng, (int32_t)(_$min.small >> 2), (int32_t)(_$max.small >> 2));
+                return I_small(r);
+            }
+
+            int32_t cmp = Int$compare_value(_$min, _$max);
+            if (cmp > 0)
+                fail("Random minimum value (", _$min, ") is larger than the maximum value (", _$max, ")");
+            if (cmp == 0) return _$min;
+
+            mpz_t range_size;
+            mpz_init_set_int(range_size, _$max);
+            if (_$min.small & 1) {
+                mpz_t min_mpz;
+                mpz_init_set_si(min_mpz, _$min.small >> 2);
+                mpz_sub(range_size, range_size, min_mpz);
+            } else {
+                mpz_sub(range_size, range_size, *_$min.big);
+            }
+
+            gmp_randstate_t gmp_rng;
+            gmp_randinit_default(gmp_rng);
+            int64_t seed = _$random$RandomNumberGenerator$int64(_$rng, INT64_MIN, INT64_MAX);
+            gmp_randseed_ui(gmp_rng, (unsigned long)seed);
+
+            mpz_t r;
+            mpz_init(r);
+            mpz_urandomm(r, gmp_rng, range_size);
+
+            gmp_randclear(gmp_rng);
+            Int$plus(_$min, Int$from_mpz(r));
+        }
+
+
+func main():
+    >> rng := RandomNumberGenerator.new()
+    >> rng:num()
+    >> rng:num()
+    >> rng:num()
+    >> rng:num(0, 100)
+    >> rng:byte()
+    >> rng:bytes(20)
+    # >> rng:int(1, 100)
+    # >> rng:int(1, 100)
+    # >> rng:int(1, 100)
+    # >> rng:int(1, 100)
diff --git a/examples/random/sysrandom.h b/examples/random/sysrandom.h
new file mode 100644
index 0000000..ea29296
--- /dev/null
+++ b/examples/random/sysrandom.h
@@ -0,0 +1,14 @@
+#pragma once
+
+#if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__) || defined(__APPLE__)
+static ssize_t getrandom(void *buf, size_t buflen, unsigned int flags) {
+    (void)flags;
+    arc4random_buf(buf, buflen);
+    return buflen;
+}
+#elif defined(__linux__)
+// Use getrandom()
+#   include <sys/random.h>
+#else
+    #error "Unsupported platform for secure random number generation"
+#endif
diff --git a/src/compile.c b/src/compile.c
index 43b9ef1..5dc09e4 100644
--- a/src/compile.c
+++ b/src/compile.c
@@ -12,6 +12,7 @@
 #include "cordhelpers.h"
 #include "enums.h"
 #include "environment.h"
+#include "parse.h"
 #include "stdlib/integers.h"
 #include "stdlib/nums.h"
 #include "stdlib/paths.h"
@@ -495,8 +496,7 @@ PUREFUNC CORD compile_unsigned_type(type_t *t)
 
 CORD compile_type(type_t *t)
 {
-    if (t == RNG_TYPE) return "RNG_t";
-    else if (t == PATH_TYPE) return "Path_t";
+    if (t == PATH_TYPE) return "Path_t";
     else if (t == PATH_TYPE_TYPE) return "PathType_t";
 
     switch (t->tag) {
@@ -2990,7 +2990,6 @@ CORD compile(env_t *env, ast_t *ast)
             type_t *item_t = Match(self_value_t, ArrayType)->item_type;
             CORD padded_item_size = CORD_all("sizeof(", compile_type(item_t), ")");
 
-            ast_t *default_rng = FakeAST(InlineCCode, .code="default_rng", .type=RNG_TYPE);
             if (streq(call->name, "insert")) {
                 EXPECT_POINTER("an", "array");
                 arg_t *arg_spec = new(arg_t, .name="item", .type=item_t,
@@ -3015,36 +3014,40 @@ CORD compile(env_t *env, ast_t *ast)
                                       .next=new(arg_t, .name="max_count", .type=INT_TYPE, .default_val=FakeAST(Int, .str="-1")));
                 return CORD_all("Array$remove_item_value(", self, ", ", compile_arguments(env, ast, arg_spec, call->args), ", ",
                                 compile_type_info(self_value_t), ")");
-            } else if (streq(call->name, "random")) {
-                self = compile_to_pointer_depth(env, call->self, 0, false);
-                arg_t *arg_spec = new(arg_t, .name="rng", .type=RNG_TYPE, .default_val=default_rng);
-                return CORD_all("Array$random_value(", self, ", ", compile_arguments(env, ast, arg_spec, call->args), ", ", compile_type(item_t), ")");
             } else if (streq(call->name, "has")) {
                 self = compile_to_pointer_depth(env, call->self, 0, false);
                 arg_t *arg_spec = new(arg_t, .name="item", .type=item_t);
                 return CORD_all("Array$has_value(", self, ", ", compile_arguments(env, ast, arg_spec, call->args), ", ",
                                 compile_type_info(self_value_t), ")");
             } else if (streq(call->name, "sample")) {
+                type_t *random_num_type = parse_type_string(env, "func(->Num)?");
+                ast_t *none_rng = parse_expression("none:func(->Num)");
                 self = compile_to_pointer_depth(env, call->self, 0, false);
                 arg_t *arg_spec = new(arg_t, .name="count", .type=INT_TYPE,
                     .next=new(arg_t, .name="weights", .type=Type(ArrayType, .item_type=Type(NumType)),
                               .default_val=FakeAST(None, .type=new(type_ast_t, .tag=ArrayTypeAST,
                                    .__data.ArrayTypeAST.item=new(type_ast_t, .tag=VarTypeAST, .__data.VarTypeAST.name="Num"))),
-                              .next=new(arg_t, .name="rng", .type=RNG_TYPE, .default_val=default_rng)));
+                              .next=new(arg_t, .name="random", .type=random_num_type, .default_val=none_rng)));
                 return CORD_all("Array$sample(", self, ", ", compile_arguments(env, ast, arg_spec, call->args), ", ",
                                 padded_item_size, ")");
             } else if (streq(call->name, "shuffle")) {
+                type_t *random_int64_type = parse_type_string(env, "func(min,max:Int64->Int64)?");
+                ast_t *none_rng = parse_expression("none:func(min,max:Int64->Int64)");
                 EXPECT_POINTER("an", "array");
-                arg_t *arg_spec = new(arg_t, .name="rng", .type=RNG_TYPE, .default_val=default_rng);
+                arg_t *arg_spec = new(arg_t, .name="random", .type=random_int64_type, .default_val=none_rng);
                 return CORD_all("Array$shuffle(", self, ", ", compile_arguments(env, ast, arg_spec, call->args), ", ", padded_item_size, ")");
             } else if (streq(call->name, "shuffled")) {
+                type_t *random_int64_type = parse_type_string(env, "func(min,max:Int64->Int64)?");
+                ast_t *none_rng = parse_expression("none:func(min,max:Int64->Int64)");
                 self = compile_to_pointer_depth(env, call->self, 0, false);
-                arg_t *arg_spec = new(arg_t, .name="rng", .type=RNG_TYPE, .default_val=default_rng);
+                arg_t *arg_spec = new(arg_t, .name="random", .type=random_int64_type, .default_val=none_rng);
                 return CORD_all("Array$shuffled(", self, ", ", compile_arguments(env, ast, arg_spec, call->args), ", ", padded_item_size, ")");
-            } else if (streq(call->name, "slice")) {
-                self = compile_to_pointer_depth(env, call->self, 0, true);
-                arg_t *arg_spec = new(arg_t, .name="first", .type=INT_TYPE, .next=new(arg_t, .name="last", .type=INT_TYPE));
-                return CORD_all("Array$slice(", self, ", ", compile_arguments(env, ast, arg_spec, call->args), ")");
+            } else if (streq(call->name, "random")) {
+                type_t *random_int64_type = parse_type_string(env, "func(min,max:Int64->Int64)?");
+                ast_t *none_rng = parse_expression("none:func(min,max:Int64->Int64)");
+                self = compile_to_pointer_depth(env, call->self, 0, false);
+                arg_t *arg_spec = new(arg_t, .name="random", .type=random_int64_type, .default_val=none_rng);
+                return CORD_all("Array$random_value(", self, ", ", compile_arguments(env, ast, arg_spec, call->args), ", ", compile_type(item_t), ")");
             } else if (streq(call->name, "sort") || streq(call->name, "sorted")) {
                 if (streq(call->name, "sort"))
                     EXPECT_POINTER("an", "array");
@@ -3755,8 +3758,7 @@ CORD compile(env_t *env, ast_t *ast)
 
 CORD compile_type_info(type_t *t)
 {
-    if (t == RNG_TYPE) return "&RNG$info";
-    else if (t == PATH_TYPE) return "&Path$info";
+    if (t == PATH_TYPE) return "&Path$info";
     else if (t == PATH_TYPE_TYPE) return "&PathType$info";
 
     switch (t->tag) {
@@ -4036,8 +4038,10 @@ CORD compile_function(env_t *env, CORD name_code, ast_t *ast, CORD *staticdefs)
         OptionalInt64_t cache_size = Int64$parse(Text$from_str(Match(cache, Int)->str));
         CORD pop_code = CORD_EMPTY;
         if (cache->tag == Int && !cache_size.is_none && cache_size.value > 0) {
+            // FIXME: this currently just deletes the first entry, but this should be more like a
+            // least-recently-used cache eviction policy or least-frequently-used
             pop_code = CORD_all("if (cache.entries.length > ", CORD_asprintf("%ld", cache_size.value),
-                                ") Table$remove(&cache, cache.entries.data + cache.entries.stride*RNG$int64(default_rng, 0, cache.entries.length-1), table_type);\n");
+                                ") Table$remove(&cache, cache.entries.data + cache.entries.stride*0, table_type);\n");
         }
 
         if (!args->next) {
diff --git a/src/environment.c b/src/environment.c
index 6822502..af697c5 100644
--- a/src/environment.c
+++ b/src/environment.c
@@ -13,7 +13,6 @@
 #include "typecheck.h"
 
 type_t *TEXT_TYPE = NULL;
-type_t *RNG_TYPE = NULL;
 public type_t *PATH_TYPE = NULL;
 public type_t *PATH_TYPE_TYPE = NULL;
 
@@ -67,7 +66,6 @@ env_t *global_env(void)
     (void)bind_type(env, "Memory", Type(MemoryType));
     PATH_TYPE_TYPE = declare_type(env, "enum PathType(Relative, Absolute, Home)");
     PATH_TYPE = declare_type(env, "struct Path(type:PathType, components:[Text])");
-    RNG_TYPE = declare_type(env, "struct RNG(state:@Memory)");
 
     typedef struct {
         const char *name, *code, *type_str;
@@ -324,22 +322,6 @@ env_t *global_env(void)
             {"write_unique", "Path$write_unique", "func(path:Path, text:Text -> Path)"},
             {"write_unique_bytes", "Path$write_unique_bytes", "func(path:Path, bytes:[Byte] -> Path)"},
         )},
-        // RNG must come after Path so we can read bytes from /dev/urandom
-        {"RNG", RNG_TYPE, "RNG_t", "RNG", TypedArray(ns_entry_t,
-            {"bool", "RNG$bool", "func(rng:RNG, p=0.5 -> Bool)"},
-            {"byte", "RNG$byte", "func(rng:RNG -> Byte)"},
-            {"bytes", "RNG$bytes", "func(rng:RNG, count:Int -> [Byte])"},
-            {"copy", "RNG$copy", "func(rng:RNG -> RNG)"},
-            {"int", "RNG$int", "func(rng:RNG, min,max:Int -> Int)"},
-            {"int16", "RNG$int16", "func(rng:RNG, min=Int16.min, max=Int16.max -> Int16)"},
-            {"int32", "RNG$int32", "func(rng:RNG, min=Int32.min, max=Int32.max -> Int32)"},
-            {"int64", "RNG$int64", "func(rng:RNG, min=Int64.min, max=Int64.max -> Int64)"},
-            {"int8", "RNG$int8", "func(rng:RNG, min=Int8.min, max=Int8.max -> Int8)"},
-            {"new", "RNG$new", "func(seed=(/dev/urandom):read_bytes(40)! -> RNG)"},
-            {"num", "RNG$num", "func(rng:RNG, min=0.0, max=1.0 -> Num)"},
-            {"num32", "RNG$num32", "func(rng:RNG, min=Num32(0.0), max=Num32(1.0) -> Num32)"},
-            {"set_seed", "RNG$set_seed", "func(rng:RNG, seed:[Byte])"},
-        )},
         {"Text", TEXT_TYPE, "Text_t", "Text$info", TypedArray(ns_entry_t,
             {"as_c_string", "Text$as_c_string", "func(text:Text -> CString)"},
             {"at", "Text$cluster", "func(text:Text, index:Int -> Text)"},
@@ -512,7 +494,6 @@ env_t *global_env(void)
                      {"Path$escape_path", "func(path:Path -> Path)"},
                      {"Int$value_as_text", "func(i:Int -> Path)"});
     ADD_CONSTRUCTORS("CString", {"Text$as_c_string", "func(text:Text -> CString)"});
-    ADD_CONSTRUCTORS("RNG", {"RNG$new", "func(-> RNG)"});
 #undef ADD_CONSTRUCTORS
 
     set_binding(namespace_env(env, "Path"), "from_text",
@@ -524,7 +505,6 @@ env_t *global_env(void)
         const char *name, *code, *type_str;
     } global_vars[] = {
         {"USE_COLOR", "USE_COLOR", "Bool"},
-        {"random", "default_rng", "RNG"},
         {"say", "say", "func(text:Text, newline=yes)"},
         {"print", "say", "func(text:Text, newline=yes)"},
         {"ask", "ask", "func(prompt:Text, bold=yes, force_tty=yes -> Text?)"},
diff --git a/src/environment.h b/src/environment.h
index bc0d55a..fce6bc9 100644
--- a/src/environment.h
+++ b/src/environment.h
@@ -89,7 +89,6 @@ void set_binding(env_t *env, const char *name, type_t *type, CORD code);
 binding_t *get_namespace_binding(env_t *env, ast_t *self, const char *name);
 #define code_err(ast, ...) compiler_err((ast)->file, (ast)->start, (ast)->end, __VA_ARGS__)
 extern type_t *TEXT_TYPE;
-extern type_t *RNG_TYPE;
 extern type_t *PATH_TYPE;
 extern type_t *PATH_TYPE_TYPE;
 
diff --git a/src/parse.c b/src/parse.c
index 2e3e2ec..9757613 100644
--- a/src/parse.c
+++ b/src/parse.c
@@ -2442,8 +2442,9 @@ ast_t *parse_file(const char *path, jmp_buf *on_err) {
 
     // If cache is getting too big, evict a random entry:
     if (cached.entries.length > PARSE_CACHE_SIZE) {
-        uint32_t i = arc4random_uniform(cached.entries.length);
-        struct {const char *path; ast_t *ast; } *to_remove = Table$entry(cached, i+1);
+        // FIXME: this currently evicts the first entry, but it should be more like
+        // an LRU cache
+        struct {const char *path; ast_t *ast; } *to_remove = Table$entry(cached, 1);
         Table$str_remove(&cached, to_remove->path);
     }
 
@@ -2484,7 +2485,24 @@ ast_t *parse(const char *str) {
     pos = ast->end;
     whitespace(&pos);
     if (pos < file->text + file->len && *pos != '\0')
-        parser_err(&ctx, pos, pos + strlen(pos), "I couldn't parse this part of the file");
+        parser_err(&ctx, pos, pos + strlen(pos), "I couldn't parse this part of the string");
+    return ast;
+}
+
+ast_t *parse_expression(const char *str) {
+    file_t *file = spoof_file("<string>", str);
+    parse_ctx_t ctx = {
+        .file=file,
+        .on_err=NULL,
+    };
+
+    const char *pos = file->text;
+    whitespace(&pos);
+    ast_t *ast = parse_extended_expr(&ctx, pos);
+    pos = ast->end;
+    whitespace(&pos);
+    if (pos < file->text + file->len && *pos != '\0')
+        parser_err(&ctx, pos, pos + strlen(pos), "I couldn't parse this part of the string");
     return ast;
 }
 
diff --git a/src/parse.h b/src/parse.h
index 95b2ff9..4de2565 100644
--- a/src/parse.h
+++ b/src/parse.h
@@ -9,5 +9,6 @@
 type_ast_t *parse_type_str(const char *str);
 ast_t *parse_file(const char *path, jmp_buf *on_err);
 ast_t *parse(const char *str);
+ast_t *parse_expression(const char *str);
 
 // vim: ts=4 sw=0 et cino=L2,l1,(0,W4,m1,\:0
diff --git a/src/stdlib/arrays.c b/src/stdlib/arrays.c
index 6579536..b018012 100644
--- a/src/stdlib/arrays.c
+++ b/src/stdlib/arrays.c
@@ -10,7 +10,6 @@
 #include "math.h"
 #include "metamethods.h"
 #include "optionals.h"
-#include "rng.h"
 #include "tables.h"
 #include "text.h"
 #include "util.h"
@@ -271,33 +270,63 @@ public Array_t Array$sorted(Array_t arr, Closure_t comparison, int64_t padded_it
     return arr;
 }
 
-public void Array$shuffle(Array_t *arr, RNG_t rng, int64_t padded_item_size)
+#if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__) || defined(__APPLE__)
+static ssize_t getrandom(void *buf, size_t buflen, unsigned int flags) {
+    (void)flags;
+    arc4random_buf(buf, buflen);
+    return buflen;
+}
+#elif defined(__linux__)
+// Use getrandom()
+#   include <sys/random.h>
+#else
+    #error "Unsupported platform for secure random number generation"
+#endif
+
+static int64_t _default_random_int64(int64_t min, int64_t max, void *userdata)
+{
+    (void)userdata;
+    if (min > max) fail("Random minimum value (", min, ") is larger than the maximum value (", max, ")");
+    if (min == max) return min;
+    uint64_t range = (uint64_t)max - (uint64_t)min + 1;
+    uint64_t min_r = -range % range;
+    uint64_t r;
+    for (;;) {
+        getrandom(&r, sizeof(r), 0);
+        if (r >= min_r) break;
+    }
+    return (int64_t)((uint64_t)min + (r % range));
+}
+
+public void Array$shuffle(Array_t *arr, OptionalClosure_t random_int64, int64_t padded_item_size)
 {
     if (arr->data_refcount != 0 || (int64_t)arr->stride != padded_item_size)
         Array$compact(arr, padded_item_size);
 
+    int64_t (*rng_fn)(int64_t, int64_t, void*) = random_int64.fn ? random_int64.fn : _default_random_int64;
     char tmp[padded_item_size];
     for (int64_t i = arr->length-1; i > 1; i--) {
-        int64_t j = RNG$int64(rng, 0, i);
+        int64_t j = rng_fn(0, i, random_int64.userdata);
         memcpy(tmp, arr->data + i*padded_item_size, (size_t)padded_item_size);
         memcpy((void*)arr->data + i*padded_item_size, arr->data + j*padded_item_size, (size_t)padded_item_size);
         memcpy((void*)arr->data + j*padded_item_size, tmp, (size_t)padded_item_size);
     }
 }
 
-public Array_t Array$shuffled(Array_t arr, RNG_t rng, int64_t padded_item_size)
+public Array_t Array$shuffled(Array_t arr, Closure_t random_int64, int64_t padded_item_size)
 {
     Array$compact(&arr, padded_item_size);
-    Array$shuffle(&arr, rng, padded_item_size);
+    Array$shuffle(&arr, random_int64, padded_item_size);
     return arr;
 }
 
-public void *Array$random(Array_t arr, RNG_t rng)
+public void *Array$random(Array_t arr, OptionalClosure_t random_int64)
 {
     if (arr.length == 0)
         return NULL; // fail("Cannot get a random item from an empty array!");
 
-    int64_t index = RNG$int64(rng, 0, arr.length-1);
+    int64_t (*rng_fn)(int64_t, int64_t, void*) = random_int64.fn;
+    int64_t index = rng_fn(0, arr.length-1, random_int64.userdata);
     return arr.data + arr.stride*index;
 }
 
@@ -314,7 +343,22 @@ public Table_t Array$counts(Array_t arr, const TypeInfo_t *type)
     return counts;
 }
 
-public Array_t Array$sample(Array_t arr, Int_t int_n, Array_t weights, RNG_t rng, int64_t padded_item_size)
+static double _default_random_num(void *userdata)
+{
+    (void)userdata;
+    union {
+        Num_t num;
+        uint64_t bits;
+    } r = {.bits=0}, one = {.num=1.0};
+    getrandom((uint8_t*)&r, sizeof(r), 0);
+
+    // Set r.num to 1.<random-bits>
+    r.bits &= ~(0xFFFULL << 52);
+    r.bits |= (one.bits & (0xFFFULL << 52));
+    return r.num - 1.0;
+}
+
+public Array_t Array$sample(Array_t arr, Int_t int_n, Array_t weights, OptionalClosure_t random_num, int64_t padded_item_size)
 {
     int64_t n = Int64$from_int(int_n, false);
     if (n < 0)
@@ -331,14 +375,6 @@ public Array_t Array$sample(Array_t arr, Int_t int_n, Array_t weights, RNG_t rng
         .length=n,
         .stride=padded_item_size, .atomic=arr.atomic};
 
-    if (weights.length < 0) {
-        for (int64_t i = 0; i < n; i++) {
-            int64_t index = RNG$int64(rng, 0, arr.length-1);
-            memcpy(selected.data + i*padded_item_size, arr.data + arr.stride*index, (size_t)padded_item_size);
-        }
-        return selected;
-    }
-
     if (weights.length != arr.length)
         fail("Array has ", (int64_t)arr.length, " elements, but there are ", (int64_t)weights.length, " weights given");
 
@@ -396,8 +432,9 @@ public Array_t Array$sample(Array_t arr, Int_t int_n, Array_t weights, RNG_t rng
         if (aliases[i].alias == -1)
             aliases[i].alias = i;
 
+    double (*rng_fn)(void*) = random_num.fn ? random_num.fn : _default_random_num;
     for (int64_t i = 0; i < n; i++) {
-        double r = RNG$num(rng, 0, arr.length);
+        double r = (double)arr.length * rng_fn(random_num.userdata);
         int64_t index = (int64_t)r;
         if ((r - (double)index) > aliases[index].odds)
             index = aliases[index].alias;
diff --git a/src/stdlib/arrays.h b/src/stdlib/arrays.h
index e286dfd..9f5f3d0 100644
--- a/src/stdlib/arrays.h
+++ b/src/stdlib/arrays.h
@@ -82,11 +82,11 @@ OptionalInt_t Array$find(Array_t arr, void *item, const TypeInfo_t *type);
 OptionalInt_t Array$first(Array_t arr, Closure_t predicate);
 void Array$sort(Array_t *arr, Closure_t comparison, int64_t padded_item_size);
 Array_t Array$sorted(Array_t arr, Closure_t comparison, int64_t padded_item_size);
-void Array$shuffle(Array_t *arr, RNG_t rng, int64_t padded_item_size);
-Array_t Array$shuffled(Array_t arr, RNG_t rng, int64_t padded_item_size);
-void *Array$random(Array_t arr, RNG_t rng);
-#define Array$random_value(arr, rng, t) ({ Array_t _arr = arr; if (_arr.length == 0) fail("Cannot get a random value from an empty array!"); *(t*)Array$random(_arr, rng); })
-Array_t Array$sample(Array_t arr, Int_t n, Array_t weights, RNG_t rng, int64_t padded_item_size);
+void Array$shuffle(Array_t *arr, OptionalClosure_t random_int64, int64_t padded_item_size);
+Array_t Array$shuffled(Array_t arr, OptionalClosure_t random_int64, int64_t padded_item_size);
+void *Array$random(Array_t arr, OptionalClosure_t random_int64);
+#define Array$random_value(arr, random_int64, t) ({ Array_t _arr = arr; if (_arr.length == 0) fail("Cannot get a random value from an empty array!"); *(t*)Array$random(_arr, random_int64); })
+Array_t Array$sample(Array_t arr, Int_t n, Array_t weights, Closure_t random_num, int64_t padded_item_size);
 Table_t Array$counts(Array_t arr, const TypeInfo_t *type);
 void Array$clear(Array_t *array);
 void Array$compact(Array_t *arr, int64_t padded_item_size);
diff --git a/src/stdlib/datatypes.h b/src/stdlib/datatypes.h
index 26bd9c3..6f3b767 100644
--- a/src/stdlib/datatypes.h
+++ b/src/stdlib/datatypes.h
@@ -105,8 +105,6 @@ typedef struct {
 } Path_t;
 #define OptionalPath_t Path_t
 
-typedef struct RNGState_t* RNG_t;
-
 #define OptionalBool_t uint8_t
 #define OptionalArray_t Array_t
 #define OptionalTable_t Table_t
diff --git a/src/stdlib/rng.c b/src/stdlib/rng.c
deleted file mode 100644
index ffc2808..0000000
--- a/src/stdlib/rng.c
+++ /dev/null
@@ -1,274 +0,0 @@
-// Random Number Generator (RNG) implementation based on ChaCha
-
-#include <ctype.h>
-#include <err.h>
-#include <gc.h>
-#include <gmp.h>
-#include <stdbool.h>
-#include <stdint.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/param.h>
-
-#include "arrays.h"
-#include "datatypes.h"
-#include "rng.h"
-#include "text.h"
-#include "util.h"
-
-#include "chacha.h"
-
-struct RNGState_t {
-    chacha_ctx chacha;
-    size_t unused_bytes;
-    uint8_t random_bytes[1024];
-};
-
-#ifdef __TINYC__
-// TinyCC doesn't implement _Thread_local
-public RNG_t default_rng = (struct RNGState_t[1]){};
-#else
-public _Thread_local RNG_t default_rng = (struct RNGState_t[1]){};
-#endif
-
-PUREFUNC static Text_t RNG$as_text(const void *rng, bool colorize, const TypeInfo_t*)
-{
-    if (!rng) return Text("RNG");
-    return Text$format(colorize ? "\x1b[34;1mRNG(%p)\x1b[m" : "RNG(%p)", *(RNG_t**)rng);
-}
-
-#define KEYSZ 32
-#define IVSZ 8
-
-public void RNG$set_seed(RNG_t rng, Array_t seed)
-{
-    uint8_t seed_bytes[KEYSZ + IVSZ] = {};
-    for (int64_t i = 0; i < (int64_t)sizeof(seed_bytes); i++)
-        seed_bytes[i] = i < seed.length ? *(uint8_t*)(seed.data + i*seed.stride) : 0;
-
-    rng->unused_bytes = 0;
-    chacha_keysetup(&rng->chacha, seed_bytes, KEYSZ/8);
-    chacha_ivsetup(&rng->chacha, seed_bytes + KEYSZ);
-}
-
-public RNG_t RNG$copy(RNG_t rng)
-{
-    RNG_t copy = GC_MALLOC_ATOMIC(sizeof(struct RNGState_t));
-    *copy = *rng;
-    return copy;
-}
-
-public RNG_t RNG$new(Array_t seed)
-{
-    RNG_t rng = GC_MALLOC_ATOMIC(sizeof(struct RNGState_t));
-    RNG$set_seed(rng, seed);
-    return rng;
-}
-
-static void rekey(RNG_t rng)
-{
-    // Fill the buffer with the keystream
-    chacha_encrypt_bytes(&rng->chacha, rng->random_bytes, rng->random_bytes, sizeof(rng->random_bytes));
-    // Immediately reinitialize for backtracking resistance
-    chacha_keysetup(&rng->chacha, rng->random_bytes, KEYSZ/8);
-    chacha_ivsetup(&rng->chacha, rng->random_bytes + KEYSZ);
-#ifdef __APPLE__
-    bzero(rng->random_bytes, KEYSZ + IVSZ);
-#else
-    explicit_bzero(rng->random_bytes, KEYSZ + IVSZ);
-#endif
-    rng->unused_bytes = sizeof(rng->random_bytes) - KEYSZ - IVSZ;
-    assert(rng->unused_bytes <= sizeof(rng->random_bytes));
-}
-
-static void random_bytes(RNG_t rng, uint8_t *dest, size_t needed)
-{
-    while (needed > 0) {
-        assert(rng->unused_bytes <= sizeof(rng->random_bytes));
-        if (rng->unused_bytes == 0)
-            rekey(rng);
-
-        size_t batch_size = MIN(needed, rng->unused_bytes);
-        uint8_t *batch_src = rng->random_bytes + sizeof(rng->random_bytes) - rng->unused_bytes;
-        memcpy(dest, batch_src, batch_size);
-        memset(batch_src, 0, batch_size);
-        rng->unused_bytes -= batch_size;
-        dest += batch_size;
-        needed -= batch_size;
-        assert(rng->unused_bytes <= sizeof(rng->random_bytes));
-    }
-}
-
-public Bool_t RNG$bool(RNG_t rng, Num_t p)
-{
-    if (p == 0.5) {
-        uint8_t b;
-        random_bytes(rng, &b, sizeof(b));
-        return b & 1;
-    } else {
-        return RNG$num(rng, 0.0, 1.0) < p;
-    }
-}
-
-public Int_t RNG$int(RNG_t rng, Int_t min, Int_t max)
-{
-    if (likely(((min.small & max.small) & 1) != 0)) {
-        int32_t r = RNG$int32(rng, (int32_t)(min.small >> 2), (int32_t)(max.small >> 2));
-        return I_small(r);
-    }
-
-    int32_t cmp = Int$compare_value(min, max);
-    if (cmp > 0)
-        fail("Random minimum value (", min, ") is larger than the maximum value (", max, ")");
-    if (cmp == 0) return min;
-
-    mpz_t range_size;
-    mpz_init_set_int(range_size, max);
-    if (min.small & 1) {
-        mpz_t min_mpz;
-        mpz_init_set_si(min_mpz, min.small >> 2);
-        mpz_sub(range_size, range_size, min_mpz);
-    } else {
-        mpz_sub(range_size, range_size, *min.big);
-    }
-
-    gmp_randstate_t gmp_rng;
-    gmp_randinit_default(gmp_rng);
-    gmp_randseed_ui(gmp_rng, (unsigned long)RNG$int64(rng, INT64_MIN, INT64_MAX));
-
-    mpz_t r;
-    mpz_init(r);
-    mpz_urandomm(r, gmp_rng, range_size);
-
-    gmp_randclear(gmp_rng);
-    return Int$plus(min, Int$from_mpz(r));
-}
-
-public Int64_t RNG$int64(RNG_t rng, Int64_t min, Int64_t max)
-{
-    if (min > max) fail("Random minimum value (", min, ") is larger than the maximum value (", max, ")");
-    if (min == max) return min;
-    if (min == INT64_MIN && max == INT64_MAX) {
-        int64_t r;
-        random_bytes(rng, (uint8_t*)&r, sizeof(r));
-        return r;
-    }
-    uint64_t range = (uint64_t)max - (uint64_t)min + 1;
-    uint64_t min_r = -range % range;
-    uint64_t r;
-    for (;;) {
-        random_bytes(rng, (uint8_t*)&r, sizeof(r));
-        if (r >= min_r) break;
-    }
-    return (int64_t)((uint64_t)min + (r % range));
-}
-
-public Int32_t RNG$int32(RNG_t rng, Int32_t min, Int32_t max)
-{
-    if (min > max) fail("Random minimum value (", min, ") is larger than the maximum value (", max, ")");
-    if (min == max) return min;
-    if (min == INT32_MIN && max == INT32_MAX) {
-        int32_t r;
-        random_bytes(rng, (uint8_t*)&r, sizeof(r));
-        return r;
-    }
-    uint32_t range = (uint32_t)max - (uint32_t)min + 1;
-    uint32_t min_r = -range % range;
-    uint32_t r;
-    for (;;) {
-        random_bytes(rng, (uint8_t*)&r, sizeof(r));
-        if (r >= min_r) break;
-    }
-    return (int32_t)((uint32_t)min + (r % range));
-}
-
-public Int16_t RNG$int16(RNG_t rng, Int16_t min, Int16_t max)
-{
-    if (min > max) fail("Random minimum value (", min, ") is larger than the maximum value (", max, ")");
-    if (min == max) return min;
-    if (min == INT16_MIN && max == INT16_MAX) {
-        int16_t r;
-        random_bytes(rng, (uint8_t*)&r, sizeof(r));
-        return r;
-    }
-    uint16_t range = (uint16_t)max - (uint16_t)min + 1;
-    uint16_t min_r = -range % range;
-    uint16_t r;
-    for (;;) {
-        random_bytes(rng, (uint8_t*)&r, sizeof(r));
-        if (r >= min_r) break;
-    }
-    return (int16_t)((uint16_t)min + (r % range));
-}
-
-public Int8_t RNG$int8(RNG_t rng, Int8_t min, Int8_t max)
-{
-    if (min > max) fail("Random minimum value (", min, ") is larger than the maximum value (", max, ")");
-    if (min == max) return min;
-    if (min == INT8_MIN && max == INT8_MAX) {
-        int8_t r;
-        random_bytes(rng, (uint8_t*)&r, sizeof(r));
-        return r;
-    }
-    uint8_t range = (uint8_t)max - (uint8_t)min + 1;
-    uint8_t min_r = -range % range;
-    uint8_t r;
-    for (;;) {
-        random_bytes(rng, (uint8_t*)&r, sizeof(r));
-        if (r >= min_r) break;
-    }
-    return (int8_t)((uint8_t)min + (r % range));
-}
-
-public Num_t RNG$num(RNG_t rng, Num_t min, Num_t max)
-{
-    if (min > max) fail("Random minimum value (", min, ") is larger than the maximum value (", max, ")");
-    if (min == max) return min;
-
-    union {
-        Num_t num;
-        uint64_t bits;
-    } r = {.bits=0}, one = {.num=1.0};
-    random_bytes(rng, (void*)&r, sizeof(r));
-
-    // Set r.num to 1.<random-bits>
-    r.bits &= ~(0xFFFULL << 52);
-    r.bits |= (one.bits & (0xFFFULL << 52));
-
-    r.num -= 1.0;
-
-    if (min == 0.0 && max == 1.0)
-        return r.num;
-
-    return (1.0-r.num)*min + r.num*max;
-}
-
-public Num32_t RNG$num32(RNG_t rng, Num32_t min, Num32_t max)
-{
-    return (Num32_t)RNG$num(rng, (Num_t)min, (Num_t)max);
-}
-
-public Byte_t RNG$byte(RNG_t rng)
-{
-    Byte_t b;
-    random_bytes(rng, &b, sizeof(b));
-    return b;
-}
-
-public Array_t RNG$bytes(RNG_t rng, Int_t count)
-{
-    int64_t n = Int64$from_int(count, false);
-    Byte_t *r = GC_MALLOC_ATOMIC(sizeof(Byte_t[n]));
-    random_bytes(rng, r, sizeof(Byte_t[n]));
-    return (Array_t){.data=r, .length=n, .stride=1, .atomic=1};
-}
-
-public const TypeInfo_t RNG$info = {
-    .size=sizeof(void*),
-    .align=__alignof__(void*),
-    .metamethods={
-        .as_text=RNG$as_text,
-    },
-};
-
-// vim: ts=4 sw=0 et cino=L2,l1,(0,W4,m1,\:0
diff --git a/src/stdlib/rng.h b/src/stdlib/rng.h
deleted file mode 100644
index 34f1ca0..0000000
--- a/src/stdlib/rng.h
+++ /dev/null
@@ -1,36 +0,0 @@
-#pragma once
-
-// Random Number Generator (RNG) functions/type info
-
-#include <stdbool.h>
-#include <stdint.h>
-
-#include "datatypes.h"
-#include "types.h"
-#include "bools.h"
-#include "bytes.h"
-#include "util.h"
-
-RNG_t RNG$new(Array_t seed);
-void RNG$set_seed(RNG_t rng, Array_t seed);
-RNG_t RNG$copy(RNG_t rng);
-Bool_t RNG$bool(RNG_t rng, Num_t p);
-Int_t RNG$int(RNG_t rng, Int_t min, Int_t max);
-Int64_t RNG$int64(RNG_t rng, Int64_t min, Int64_t max);
-Int32_t RNG$int32(RNG_t rng, Int32_t min, Int32_t max);
-Int16_t RNG$int16(RNG_t rng, Int16_t min, Int16_t max);
-Int8_t RNG$int8(RNG_t rng, Int8_t min, Int8_t max);
-Byte_t RNG$byte(RNG_t rng);
-Array_t RNG$bytes(RNG_t rng, Int_t count);
-Num_t RNG$num(RNG_t rng, Num_t min, Num_t max);
-Num32_t RNG$num32(RNG_t rng, Num32_t min, Num32_t max);
-
-extern const TypeInfo_t RNG$info;
-// TinyCC doesn't implement _Thread_local
-#ifdef __TINYC__
-extern RNG_t default_rng;
-#else
-extern _Thread_local RNG_t default_rng;
-#endif
-
-// vim: ts=4 sw=0 et cino=L2,l1,(0,W4,m1,\:0
diff --git a/src/stdlib/stdlib.c b/src/stdlib/stdlib.c
index 2177397..80c53b6 100644
--- a/src/stdlib/stdlib.c
+++ b/src/stdlib/stdlib.c
@@ -21,7 +21,6 @@
 #include "metamethods.h"
 #include "nums.h"
 #include "paths.h"
-#include "rng.h"
 #include "siphash.h"
 #include "stdlib.h"
 #include "tables.h"
@@ -65,11 +64,6 @@ public void tomo_init(void)
    setlocale(LC_ALL, "");
    getrandom(TOMO_HASH_KEY, sizeof(TOMO_HASH_KEY), 0);
 
-   uint8_t *random_bytes[40] = {};
-   getrandom(random_bytes, sizeof(random_bytes), 0);
-   Array_t rng_seed = {.length=sizeof(random_bytes), .data=random_bytes, .stride=1, .atomic=1};
-   RNG$set_seed(default_rng, rng_seed);
-
    struct sigaction sigact;
    sigact.sa_sigaction = signal_handler;
    sigemptyset(&sigact.sa_mask);
diff --git a/src/stdlib/tomo.h b/src/stdlib/tomo.h
index e42b562..b5642ec 100644
--- a/src/stdlib/tomo.h
+++ b/src/stdlib/tomo.h
@@ -22,7 +22,6 @@
 #include "paths.h"
 #include "pointers.h"
 #include "print.h"
-#include "rng.h"
 #include "siphash.h"
 #include "structs.h"
 #include "tables.h"
diff --git a/test/arrays.tm b/test/arrays.tm
index 2c9f472..66819a7 100644
--- a/test/arrays.tm
+++ b/test/arrays.tm
@@ -101,7 +101,7 @@ func main():
 	>> ["A", "B", "C"]:sample(10, [1.0, 0.5, 0.0])
 
 	do:
-		>> heap := @[random:int(1, 50) for _ in 10]
+		>> heap := @[(i * 1337) mod 37 for i in 10]
 		>> heap:heapify()
 		>> heap
 		sorted := @[:Int]
@@ -109,8 +109,8 @@ func main():
 			sorted:insert(heap:heap_pop() or stop)
 		>> sorted == sorted:sorted()
 		= yes
-		for _ in 10:
-			heap:heap_push(random:int(1, 50))
+		for i in 10:
+			heap:heap_push((i*13337) mod 37)
 		>> heap
 		sorted = @[:Int]
 		repeat:
diff --git a/test/integers.tm b/test/integers.tm
index c8fd5c9..04256c8 100644
--- a/test/integers.tm
+++ b/test/integers.tm
@@ -85,12 +85,12 @@ func main():
 		= 10000000000000000000000
 
 	do:
-		for in 20:
-			>> n := random:int(-999999, 999999)
-			>> d := random:int(-999, 999)
-			!! n=$n, d=$d:
-			>> (n/d)*d + (n mod d) == n
-			= yes
+		interesting_numerators := [-999999, -100, -23, -1, 0, 1, 23, 100, 999999]
+		interesting_denominators := [-99, -20, -17, -1, 1, 17, 20, 99]
+		for n in interesting_numerators:
+			for d in interesting_denominators:
+				>> (n/d)*d + (n mod d) == n
+				= yes
 
 	>> 0:next_prime()
 	= 2
diff --git a/test/rng.tm b/test/rng.tm
deleted file mode 100644
index 1814d58..0000000
--- a/test/rng.tm
+++ /dev/null
@@ -1,40 +0,0 @@
-# Random Number Generator tests
-
-func main():
-    !! Default RNG:
-    >> random:int64()
-
-    >> original_rng := RNG.new([:Byte])
-    >> copy := original_rng:copy()
-
-    for rng in [original_rng, copy]:
-        !! RNG: $rng
-        >> rng:int(1, 1000)
-        = 921
-        >> rng:int64(1, 1000)
-        = Int64(324)
-        >> rng:int32(1, 1000)
-        = Int32(586)
-        >> rng:int16(1, 1000)
-        = Int16(453)
-        >> rng:int8(1, 100)
-        = Int8(53)
-        >> rng:byte()
-        = Byte(0xDC)
-        >> rng:bytes(10)
-        = [:Byte, 0xA0, 0x5A, 0x10, 0x3F, 0x6C, 0xD1, 0x35, 0xC2, 0x87, 0x8C]
-        >> rng:bool(p=0.8)
-        = yes
-        >> rng:num()
-        = 0.03492503353647658
-        >> rng:num32(1, 1000)
-        = Num32(761.05908)
-
-        !! Random array methods:
-        >> nums := [10*i for i in 10]
-        >> nums:shuffled(rng=rng)
-        = [30, 50, 100, 20, 90, 10, 80, 40, 70, 60]
-        >> nums:random(rng=rng)
-        = 70
-        >> nums:sample(10, weights=[1.0/Num(i) for i in nums.length], rng=rng)
-        = [10, 20, 10, 10, 30, 70, 10, 40, 60, 80]