# Qwen format probe — YAML surface

**Model:** Qwen/Qwen3-Coder-Next; single-shot; YAML dialect; converted via verified PyYAML round-trip.

---

## L0_const — ✅ green

tokens: prompt=649 completion=58

model YAML:
```yaml
module:
- m
- fn:
  - answer
  - type:
    - fn-type:
      - params: []
      - ret:
        - own:
          - con:
            - Int
  - params: []
  - body:
    - '42'
```

converted Form-A:
```
(module m (fn answer (type (fn-type (params) (ret (own (con Int))))) (params) (body 42)))
```


## L1_arith — ❌ yaml-convert

tokens: prompt=651 completion=87

model YAML:
```yaml
module:
- demo_m
- fn:
  - triple
  - type:
    - fn-type:
      - params:
        - own:
          - con:
            - Int
      - ret:
        - own:
          - con:
            - Int
  - params:
    - x
  - body:
    - app:
      - app:
        - *
      - x
      - '3'
```


**yaml-convert:**
```
converter rejected model YAML: while scanning an alias
  in "<unicode string>", line 20, column 11:
            - *
              ^
expected alphabetic or numeric character, but found '\n'
  in "<unicode string>", line 20, column 12:
            - *
               ^
```

## L2_print — ❌ yaml-convert

tokens: prompt=646 completion=94

model YAML:
```yaml
module:
- demo_c
- fn:
  - m
  - type:
    - fn-type:
      - params: []
      - ret:
        - own:
          - con:
            - Unit
      - effects:
        - IO
  - params: []
  - body:
    - seq:
      - app:
        - print
        - '7
      - do:
        - io/print_str
        - '"\n"'
```


**yaml-convert:**
```
converter rejected model YAML: while parsing a block mapping
  in "<unicode string>", line 17, column 9:
          - app:
            ^
expected <block end>, but found '<scalar>'
  in "<unicode string>", line 22, column 12:
            - '"\n"'
               ^
```

## L3_adt — ✅ green

tokens: prompt=665 completion=136

model YAML:
```yaml
module:
- demo_m
- data:
  - Light
  - ctor:
    - Red
  - ctor:
    - Green
- fn:
  - code
  - type:
    - fn-type:
      - params:
        - own:
          - con:
            - Light
      - ret:
        - own:
          - con:
            - Int
  - params:
    - l
  - body:
    - match:
      - l
      - case:
        - pat-ctor:
          - Red
        - '0'
      - case:
        - pat-ctor:
          - Green
        - '1'
```

converted Form-A:
```
(module demo_m (data Light (ctor Red) (ctor Green)) (fn code (type (fn-type (params (own (con Light))) (ret (own (con Int))))) (params l) (body (match l (case (pat-ctor Red) 0) (case (pat-ctor Green) 1)))))
```


## L4_rec — ❌ yaml-convert

tokens: prompt=677 completion=359

model YAML:
```yaml
module:
- demo_m
- data:
  - IntList
  - ctor:
    - Nil
  - ctor:
    - Cons
  - con:
    - Int
  - con:
    - IntList
- fn:
  - length
  - type:
    - fn-type:
      - params:
        - own:
          - con:
            - IntList
      - ret:
        - own:
          - con:
            - Int
  - params:
    - xs
  - body:
    - match:
      - xs
      - case:
        - pat-ctor:
          - Nil
        - '0'
      - case:
        - pat-ctor:
          - Cons
          - h
          - t
        - app:
          - +
          - '1'
          - app:
            - length
            - t
- fn:
  - main
  - type:
    - fn-type:
      - params: []
      - ret:
        - own:
          - con:
            - Unit
      - effects:
        - IO
  - params: []
  - body:
    - let:
      - xs
      - term-ctor:
        - IntList
        - Cons
        - '1'
        - term-ctor:
          - IntList
        - Cons
        - '2'
        - term-ctor:
          - IntList
        - Cons
        - '3'
        - term-ctor:
          - IntList
        - Nil
      - seq:
        - app:
          - print
          - app:
            - length
            - xs
      - do:
        - io/print_str
        - '"\n"
```


**yaml-convert:**
```
converter rejected model YAML: while scanning a quoted scalar
  in "<unicode string>", line 83, column 11:
            - '"\n"
              ^
found unexpected end of stream
  in "<unicode string>", line 83, column 16:
            - '"\n"
                   ^
```

## L5_series_len — ❌ check

tokens: prompt=945 completion=215

model YAML:
```yaml
module:
- demo_m
- fn:
  - main
  - type:
    - fn-type:
      - params: []
      - ret:
        - own:
          - con:
            - Unit
      - effects:
        - IO
  - params: []
  - body:
    - let:
      - s
      - new:
        - Series
        - con:
          - Float
        - '3'
    - let:
      - s
      - app:
        - Series.push
        - s
        - '1.0'
    - let:
      - s
      - app:
        - Series.push
        - s
        - '2.0'
    - let:
      - s
      - app:
        - Series.push
        - s
        - '3.0'
    - seq:
      - app:
        - print
      - app:
        - Series.len
      - s
    - do:
      - io/print_str
      - '"\n"'
```

converted Form-A:
```
(module demo_m (fn main (type (fn-type (params) (ret (own (con Unit))) (effects IO))) (params) (body (let s (new Series (con Float) 3)) (let s (app Series.push s 1.0)) (let s (app Series.push s 2.0)) (let s (app Series.push s 3.0)) (seq (app print) (app Series.len) s) (do io/print_str "\n"))))
```

**check:**
```
error: [surface-parse-error] parse error: expected term, got `)` at byte 134
```

## L6_series_at — ❌ check

tokens: prompt=953 completion=226

model YAML:
```yaml
module:
- demo_m
- fn:
  - main
  - type:
    - fn-type:
      - params: []
      - ret:
        - own:
          - con:
            - Unit
      - effects:
        - IO
  - params: []
  - body:
    - let:
      - s
      - new:
        - Series
        - con:
          - Float
        - '3'
    - let:
      - s1
      - app:
        - Series.push
        - s
        - '1.0'
    - let:
      - s2
      - app:
        - Series.push
        - s1
        - '2.0'
    - let:
      - s3
      - app:
        - Series.push
        - s2
        - '3.0'
    - seq:
      - app:
        - print
      - app:
        - Series.at
      - s3
      - '0'
    - do:
      - io/print_str
      - '"\n"'
```

converted Form-A:
```
(module demo_m (fn main (type (fn-type (params) (ret (own (con Unit))) (effects IO))) (params) (body (let s (new Series (con Float) 3)) (let s1 (app Series.push s 1.0)) (let s2 (app Series.push s1 2.0)) (let s3 (app Series.push s2 3.0)) (seq (app print) (app Series.at) s3 0) (do io/print_str "\n"))))
```

**check:**
```
error: [surface-parse-error] parse error: expected term, got `)` at byte 134
```

## L7_sma — ❌ check

tokens: prompt=1036 completion=469

model YAML:
```yaml
module:
- demo_m
- fn:
  - main
  - type:
    - fn-type:
      - params: []
      - ret:
        - own:
          - con:
            - Unit
      - effects:
        - IO
  - params: []
  - body:
    - let:
      - s
      - new:
        - Series
        - con:
          - Float
        - '3'
    - let:
      - s
      - app:
        - Series.push
        - s
        - '1.0'
    - let:
      - s
      - app:
        - Series.push
        - s
        - '5.0'
    - seq:
      - app:
        - print
      - app:
        - /
      - app:
        - Series.sum
      - s
      - '3.0'
    - let:
      - s
      - app:
        - Series.push
      - s
      - '3.0'
    - seq:
      - app:
        - print
      - app:
        - /
      - app:
        - Series.sum
      - s
      - '3.0'
    - let:
      - s
      - app:
        - Series.push
      - s
      - '8.0'
    - seq:
      - app:
        - print
      - app:
        - /
      - app:
        - Series.sum
      - s
      - '3.0'
    - let:
      - s
      - app:
        - Series.push
      - s
      - '6.0'
    - seq:
      - app:
        - print
      - app:
        - /
      - app:
        - Series.sum
      - s
      - '3.0'
    - let:
      - s
      - app:
        - Series.push
      - s
      - '2.0'
    - seq:
      - app:
        - print
      - app:
        - /
      - app:
        - Series.sum
      - s
      - '3.0'
    - do:
      - io/print_str
      - '"\n"'
```

converted Form-A:
```
(module demo_m (fn main (type (fn-type (params) (ret (own (con Unit))) (effects IO))) (params) (body (let s (new Series (con Float) 3)) (let s (app Series.push s 1.0)) (let s (app Series.push s 5.0)) (seq (app print) (app /) (app Series.sum) s 3.0) (let s (app Series.push) s 3.0) (seq (app print) (app /) (app Series.sum) s 3.0) (let s (app Series.push) s 8.0) (seq (app print) (app /) (app Series.sum) s 3.0) (let s (app Series.push) s 6.0) (seq (app print) (app /) (app Series.sum) s 3.0) (let s (app Series.push) s 2.0) (seq (app print) (app /) (app Series.sum) s 3.0) (do io/print_str "\n"))))
```

**check:**
```
error: [surface-parse-error] parse error: expected term, got `)` at byte 134
```


---
## Ladder

- L0_const: ✅ green
- L1_arith: ❌ yaml-convert
- L2_print: ❌ yaml-convert
- L3_adt: ✅ green
- L4_rec: ❌ yaml-convert
- L5_series_len: ❌ check
- L6_series_at: ❌ check
- L7_sma: ❌ check