From 10380e451aa9bf80f5a9008c544abc0853e9b832 Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
Date: Thu, 20 May 2021 22:34:20 +0200
Subject: [PATCH] Simplify schemas by allowing at most one of "&" or "/" in a
 definition

---
 .../packages/schema/src/compiler.ts           |   2 +-
 .../packages/schema/src/compiler/context.ts   |  11 +-
 .../schema/src/compiler/genconverter.ts       |  73 ++++-----
 .../packages/schema/src/compiler/gentype.ts   |  28 ++--
 .../schema/src/compiler/genunconverter.ts     |  96 ++++++------
 .../packages/schema/src/gen/schema.ts         | 146 +++++++-----------
 .../javascript/packages/schema/src/meta.ts    |   3 -
 .../javascript/packages/schema/src/reader.ts  | 117 ++++++--------
 schema/schema.bin                             |   6 +-
 schema/schema.prs                             |  17 +-
 10 files changed, 224 insertions(+), 275 deletions(-)

diff --git a/implementations/javascript/packages/schema/src/compiler.ts b/implementations/javascript/packages/schema/src/compiler.ts
index 4c63e25..adc7fbb 100644
--- a/implementations/javascript/packages/schema/src/compiler.ts
+++ b/implementations/javascript/packages/schema/src/compiler.ts
@@ -16,7 +16,7 @@ export function compile(env: M.Environment, schema: M.Schema, options: CompilerO
     mod.defineType(seq(`export type _embedded = `,
                        renderType(embeddedName._variant === 'false'
                            ? Type.ref('any')
-                           : typeForDefinition(mod, M.Definition.Alternative(M.Alternative.Pattern(M.Pattern.SimplePattern(M.SimplePattern.Ref(embeddedName.value)))))),
+                           : typeForDefinition(mod, M.Definition.Pattern(M.Pattern.SimplePattern(M.SimplePattern.Ref(embeddedName.value))))),
                        `;`));
     mod.defineType(`export type _val = _.Value<_embedded>;`);
 
diff --git a/implementations/javascript/packages/schema/src/compiler/context.ts b/implementations/javascript/packages/schema/src/compiler/context.ts
index e10b306..692b07b 100644
--- a/implementations/javascript/packages/schema/src/compiler/context.ts
+++ b/implementations/javascript/packages/schema/src/compiler/context.ts
@@ -46,13 +46,12 @@ export class ModuleContext {
         if (refCount > RECURSION_LIMIT) {
             throw new Error('Recursion limit exceeded');
         }
-        if (p._variant === 'Alternative' &&
-            p.value._variant === 'Pattern' &&
-            p.value.value._variant === 'SimplePattern' &&
-            p.value.value.value._variant === 'Ref')
+        if (p._variant === 'Pattern' &&
+            p.value._variant === 'SimplePattern' &&
+            p.value.value._variant === 'Ref')
         {
-            return M.lookup(refPosition(p.value.value.value.value),
-                            p.value.value.value.value,
+            return M.lookup(refPosition(p.value.value.value),
+                            p.value.value.value,
                             this.env,
                             (p) => this.derefPattern(p, refCount + 1),
                             (_modId, _modPath, pp) => this.derefPattern(pp ?? p, refCount + 1));
diff --git a/implementations/javascript/packages/schema/src/compiler/genconverter.ts b/implementations/javascript/packages/schema/src/compiler/genconverter.ts
index 4f5ad0c..df9a8c0 100644
--- a/implementations/javascript/packages/schema/src/compiler/genconverter.ts
+++ b/implementations/javascript/packages/schema/src/compiler/genconverter.ts
@@ -11,53 +11,54 @@ export function converterForDefinition(
     src: string,
     dest: string): Item[]
 {
-    if (p._variant === 'or') {
-        const alts = [p.pattern, ... p.patterns];
-        function loop(i: number): Item[] {
-            ctx.variantName = alts[i].variantLabel;
-            return [... converterForAlternative(ctx, alts[i].alternative, src, dest),
-                    ... ((i < alts.length - 1)
-                        ? [seq(`if (${dest} === void 0) `, ctx.block(() => loop(i + 1)))]
-                        : [])];
+    switch (p._variant) {
+        case 'or': {
+            const alts = [p.pattern, ... p.patterns];
+            function loop(i: number): Item[] {
+                ctx.variantName = alts[i].variantLabel;
+                return [... converterForPattern(ctx, alts[i].pattern, src, dest),
+                        ... ((i < alts.length - 1)
+                            ? [seq(`if (${dest} === void 0) `, ctx.block(() => loop(i + 1)))]
+                            : [])];
+            }
+            return loop(0);
         }
-        return loop(0);
-    } else {
-        ctx.variantName = void 0;
-        return converterForAlternative(ctx, p.value, src, dest);
+        case 'and': {
+            const pcs = [p.pattern, ... p.patterns];
+            function loop(i: number): Item[] {
+                return (i < pcs.length)
+                    ? converterFor(ctx, pcs[i], src, () => loop(i + 1))
+                    : [ctx.buildCapturedCompound(dest)];
+            }
+            return loop(0);
+        }
+        case 'Pattern':
+            ctx.variantName = void 0;
+            return converterForPattern(ctx, p.value, src, dest);
     }
 }
 
-function converterForAlternative(
+function converterForPattern(
     ctx: FunctionContext,
-    p: M.Alternative,
+    p: M.Pattern,
     src: string,
     dest: string): Item[]
 {
-    if (p._variant === 'and') {
-        const alts = [p.pattern, ... p.patterns];
-        function loop(i: number): Item[] {
-            return (i < alts.length)
-                ? converterFor(ctx, alts[i], src, () => loop(i + 1))
-                : [ctx.buildCapturedCompound(dest)];
-        }
-        return loop(0);
-    } else {
-        return converterFor(ctx, M.NamedPattern.anonymous(p.value), src, simpleValue => {
-            if (simpleValue === void 0) {
+    return converterFor(ctx, M.NamedPattern.anonymous(p), src, simpleValue => {
+        if (simpleValue === void 0) {
+            return [ctx.buildCapturedCompound(dest)];
+        } else if (ctx.variantName !== void 0) {
+            if (typeFor(ctx.mod, p).kind === 'unit') {
                 return [ctx.buildCapturedCompound(dest)];
-            } else if (ctx.variantName !== void 0) {
-                if (typeFor(ctx.mod, p.value).kind === 'unit') {
-                    return [ctx.buildCapturedCompound(dest)];
-                } else {
-                    return [ctx.withCapture('value',
-                                            simpleValue,
-                                            () => ctx.buildCapturedCompound(dest))];
-                }
             } else {
-                return [`${dest} = ${simpleValue}`];
+                return [ctx.withCapture('value',
+                                        simpleValue,
+                                        () => ctx.buildCapturedCompound(dest))];
             }
-        });
-    }
+        } else {
+            return [`${dest} = ${simpleValue}`];
+        }
+    });
 }
 
 function converterForTuple(ctx: FunctionContext,
diff --git a/implementations/javascript/packages/schema/src/compiler/gentype.ts b/implementations/javascript/packages/schema/src/compiler/gentype.ts
index a9abe6c..a8ffa67 100644
--- a/implementations/javascript/packages/schema/src/compiler/gentype.ts
+++ b/implementations/javascript/packages/schema/src/compiler/gentype.ts
@@ -4,24 +4,22 @@ import { ModuleContext } from "./context";
 import { ANY_TYPE, AtomicType, CollectionType, FieldMap, SimpleType, Type } from "./type";
 
 export function typeForDefinition(mod: ModuleContext, d: M.Definition): Type {
-    if (d._variant === 'or') {
-        return Type.union(
-            new Map([d.pattern, ... d.patterns].map(a =>
-                [a.variantLabel, typeForAlternative(mod, a.alternative)])));
-    } else {
-        return typeForAlternative(mod, d.value);
+    switch (d._variant) {
+        case 'or':
+            return Type.union(
+                new Map([d.pattern, ... d.patterns].map(a =>
+                    [a.variantLabel, typeFor(mod, a.pattern)])));
+        case 'and':
+            return typeForIntersection(mod, [d.pattern, ... d.patterns]);
+        case 'Pattern':
+            return typeFor(mod, d.value);
     }
 }
 
-export function typeForAlternative(mod: ModuleContext, a: M.Alternative): SimpleType {
-    if (a._variant === 'and') {
-        const fs = new Map();
-        gatherFields(fs, mod, a.pattern);
-        a.patterns.forEach(n => gatherFields(fs, mod, n));
-        return fs.size > 0 ? Type.record(fs) : Type.unit();
-    } else {
-        return typeFor(mod, a.value);
-    }
+export function typeForIntersection(mod: ModuleContext, ps: M.NamedPattern[]): SimpleType {
+    const fs = new Map();
+    ps.forEach(p => gatherFields(fs, mod, p));
+    return fs.size > 0 ? Type.record(fs) : Type.unit();
 }
 
 export function setType(mod: ModuleContext, p: M.SimplePattern): CollectionType {
diff --git a/implementations/javascript/packages/schema/src/compiler/genunconverter.ts b/implementations/javascript/packages/schema/src/compiler/genunconverter.ts
index d03855b..332db2f 100644
--- a/implementations/javascript/packages/schema/src/compiler/genunconverter.ts
+++ b/implementations/javascript/packages/schema/src/compiler/genunconverter.ts
@@ -2,8 +2,8 @@ import { refPosition } from '../reader';
 import * as M from '../meta';
 import { block, brackets, formatItems, Item, parens, seq } from './block';
 import { FunctionContext } from "./context";
-import { typeForAlternative } from './gentype';
 import { FieldType, renderType, SimpleType } from './type';
+import { typeFor, typeForIntersection } from './gentype';
 
 export function unconverterForDefinition(
     ctx: FunctionContext,
@@ -11,61 +11,59 @@ export function unconverterForDefinition(
     def: M.Definition,
     src: string): Item[]
 {
-    if (def._variant === 'or') {
-        return [seq(`switch (${src}._variant) `, block(
-            ... [def.pattern, ... def.patterns].map(p =>
-                seq(`case `, JSON.stringify(p.variantLabel), `: `, ctx.block(() => {
-                    const hasValueField =
-                        p.alternative._variant === 'Pattern' &&
-                        p.alternative.value._variant === 'SimplePattern';
-                    return [seq(`return `, unconverterForAlternative(
-                        ctx, name, p.alternative, hasValueField ? `${src}.value` : src))];
-                })))))];
-    } else {
-        return [seq(`return `, unconverterForAlternative(ctx, name, def.value, `${src}`))];
+    switch (def._variant) {
+        case 'or':
+            return [seq(`switch (${src}._variant) `, block(
+                ... [def.pattern, ... def.patterns].map(p =>
+                    seq(`case `, JSON.stringify(p.variantLabel), `: `, ctx.block(() => {
+                        const hasValueField = p.pattern._variant === 'SimplePattern';
+                        return [seq(`return `, unconverterForPattern(
+                            ctx, name, p.pattern, hasValueField ? `${src}.value` : src))];
+                    })))))];
+        case 'and': {
+            const ps = [def.pattern , ... def.patterns];
+            const t = typeForIntersection(ctx.mod, ps);
+            const errs: [string, InsufficientInformationError][] = [];
+            const cs = ps.flatMap(p => {
+                if (p._variant === 'anonymous' && p.value._variant === 'SimplePattern') {
+                    return [];
+                } else {
+                    try {
+                        return [unconverterForNamed(ctx, p, src, t)];
+                    } catch (e) {
+                        if (e instanceof InsufficientInformationError) {
+                            errs.push([name + '/' + (M.nameFor(p) ?? '<anonymous>'), e]);
+                            return [];
+                        }
+                        throw e;
+                    }
+                }
+            });
+            if (cs.length === 0 || errs.length > 0) {
+                throw new Error(`Cannot produce unconverter for ${name}: ` +
+                    errs.map(e => `${e[0]}: ${e[1].message}`).join(', '));
+            }
+            return [seq(`return `, (cs.length === 1)
+                ? cs[0]
+                : seq(`_.merge`, parens(`(a, b) => (a === b) ? a : void 0`, ... cs)))];
+        }
+        case 'Pattern':
+            return [seq(`return `, unconverterForPattern(ctx, name, def.value, `${src}`))];
     }
 }
 
 export class InsufficientInformationError extends Error {}
 
-function unconverterForAlternative(
-    ctx: FunctionContext,
-    name: string,
-    a: M.Alternative,
-    src: string): Item
+function unconverterForPattern(ctx: FunctionContext, name: string, a: M.Pattern, src: string): Item
 {
-    const t = typeForAlternative(ctx.mod, a);
-    if (a._variant === 'and') {
-        const errs: [string, InsufficientInformationError][] = [];
-        const cs = [a.pattern, ... a.patterns].flatMap(p => {
-            if (p._variant === 'anonymous' && p.value._variant === 'SimplePattern') {
-                return [];
-            } else {
-                try {
-                    return [unconverterForNamed(ctx, p, src, t)];
-                } catch (e) {
-                    if (e instanceof InsufficientInformationError) {
-                        errs.push([name + '/' + (M.nameFor(p) ?? '<anonymous>'), e]);
-                        return [];
-                    }
-                    throw e;
-                }
-            }
-        });
-        if (cs.length === 0 || errs.length > 0) {
-            throw new Error(`Cannot produce unconverter for ${name}: ` +
-                errs.map(e => `${e[0]}: ${e[1].message}`).join(', '));
-        }
-        return (cs.length === 1) ? cs[0] : seq(`_.merge`, parens(`(a, b) => (a === b) ? a : void 0`, ... cs));
-    } else {
-        try {
-            return unconverterFor(ctx, a.value, src, t);
-        } catch (e) {
-            if (e instanceof InsufficientInformationError) {
-                throw new Error(`Cannot produce unconverter for ${name}: ${e.message}`);
-            }
-            throw e;
+    const t = typeFor(ctx.mod, a);
+    try {
+        return unconverterFor(ctx, a, src, t);
+    } catch (e) {
+        if (e instanceof InsufficientInformationError) {
+            throw new Error(`Cannot produce unconverter for ${name}: ${e.message}`);
         }
+        throw e;
     }
 }
 
diff --git a/implementations/javascript/packages/schema/src/gen/schema.ts b/implementations/javascript/packages/schema/src/gen/schema.ts
index bd9b96e..fc9585b 100644
--- a/implementations/javascript/packages/schema/src/gen/schema.ts
+++ b/implementations/javascript/packages/schema/src/gen/schema.ts
@@ -55,12 +55,6 @@ export type Definition = (
         "pattern": NamedAlternative,
         "patterns": Array<NamedAlternative>
     } |
-    {"_variant": "Alternative", "value": Alternative}
-);
-
-export type NamedAlternative = {"variantLabel": string, "alternative": Alternative};
-
-export type Alternative = (
     {"_variant": "and", "pattern": NamedPattern, "patterns": Array<NamedPattern>} |
     {"_variant": "Pattern", "value": Pattern}
 );
@@ -103,6 +97,8 @@ export type AtomKind = (
     {"_variant": "Symbol"}
 );
 
+export type NamedAlternative = {"variantLabel": string, "pattern": Pattern};
+
 export type NamedSimplePattern = (
     {"_variant": "named", "value": NamedSimplePattern_} |
     {"_variant": "anonymous", "value": SimplePattern}
@@ -143,14 +139,8 @@ export namespace Definition {
     export function or(
         {pattern, patterns}: {pattern: NamedAlternative, patterns: Array<NamedAlternative>}
     ): Definition {return {"_variant": "or", "pattern": pattern, "patterns": patterns};};
-    export function Alternative(value: Alternative): Definition {return {"_variant": "Alternative", "value": value};};
-}
-
-export function NamedAlternative({variantLabel, alternative}: {variantLabel: string, alternative: Alternative}): NamedAlternative {return {"variantLabel": variantLabel, "alternative": alternative};}
-
-export namespace Alternative {
-    export function and({pattern, patterns}: {pattern: NamedPattern, patterns: Array<NamedPattern>}): Alternative {return {"_variant": "and", "pattern": pattern, "patterns": patterns};};
-    export function Pattern(value: Pattern): Alternative {return {"_variant": "Pattern", "value": value};};
+    export function and({pattern, patterns}: {pattern: NamedPattern, patterns: Array<NamedPattern>}): Definition {return {"_variant": "and", "pattern": pattern, "patterns": patterns};};
+    export function Pattern(value: Pattern): Definition {return {"_variant": "Pattern", "value": value};};
 }
 
 export namespace Pattern {
@@ -187,6 +177,8 @@ export namespace AtomKind {
     export function Symbol(): AtomKind {return {"_variant": "Symbol"};};
 }
 
+export function NamedAlternative({variantLabel, pattern}: {variantLabel: string, pattern: Pattern}): NamedAlternative {return {"variantLabel": variantLabel, "pattern": pattern};}
+
 export namespace NamedSimplePattern {
     export function named(value: NamedSimplePattern_): NamedSimplePattern {return {"_variant": "named", "value": value};};
     export function anonymous(value: SimplePattern): NamedSimplePattern {return {"_variant": "anonymous", "value": value};};
@@ -415,9 +407,37 @@ export function toDefinition(v: _val): undefined | Definition {
         };
     };
     if (result === void 0) {
-        let _tmp6: (Alternative) | undefined;
-        _tmp6 = toAlternative(v);
-        if (_tmp6 !== void 0) {result = {"_variant": "Alternative", "value": _tmp6};};
+        if (_.Record.isRecord<_val, _.Tuple<_val>, _embedded>(v)) {
+            let _tmp6: (null) | undefined;
+            _tmp6 = _.is(v.label, $and) ? null : void 0;
+            if (_tmp6 !== void 0) {
+                if (_.Array.isArray(v[0]) && v[0].length >= 1) {
+                    let _tmp7: (NamedPattern) | undefined;
+                    _tmp7 = toNamedPattern(v[0][0]);
+                    if (_tmp7 !== void 0) {
+                        let _tmp8: (Array<_val>) | undefined;
+                        let _tmp9: (Array<NamedPattern>) | undefined;
+                        _tmp8 = v[0].slice(1);
+                        {
+                            _tmp9 = [];
+                            for (const _tmp10 of _tmp8) {
+                                let _tmp11: (NamedPattern) | undefined;
+                                _tmp11 = toNamedPattern(_tmp10);
+                                if (_tmp11 !== void 0) {_tmp9.push(_tmp11); continue;};
+                                _tmp9 = void 0;
+                                break;
+                            };
+                            if (_tmp9 !== void 0) {result = {"_variant": "and", "pattern": _tmp7, "patterns": _tmp9};};
+                        };
+                    };
+                };
+            };
+        };
+        if (result === void 0) {
+            let _tmp12: (Pattern) | undefined;
+            _tmp12 = toPattern(v);
+            if (_tmp12 !== void 0) {result = {"_variant": "Pattern", "value": _tmp12};};
+        };
     };
     return result;
 }
@@ -435,76 +455,6 @@ export function fromDefinition(_v: Definition): _val {
                 ]
             );
         };
-        case "Alternative": {return fromAlternative(_v.value);};
-    };
-}
-
-export function asNamedAlternative(v: _val): NamedAlternative {
-    let result = toNamedAlternative(v);
-    if (result === void 0) throw new TypeError(`Invalid NamedAlternative: ${_.stringify(v)}`);
-    return result;
-}
-
-export function toNamedAlternative(v: _val): undefined | NamedAlternative {
-    let result: undefined | NamedAlternative;
-    if (_.Array.isArray(v) && v.length === 2) {
-        let _tmp0: (string) | undefined;
-        _tmp0 = typeof v[0] === 'string' ? v[0] : void 0;
-        if (_tmp0 !== void 0) {
-            let _tmp1: (Alternative) | undefined;
-            _tmp1 = toAlternative(v[1]);
-            if (_tmp1 !== void 0) {result = {"variantLabel": _tmp0, "alternative": _tmp1};};
-        };
-    };
-    return result;
-}
-
-export function fromNamedAlternative(_v: NamedAlternative): _val {return [_v["variantLabel"], fromAlternative(_v["alternative"])];}
-
-export function asAlternative(v: _val): Alternative {
-    let result = toAlternative(v);
-    if (result === void 0) throw new TypeError(`Invalid Alternative: ${_.stringify(v)}`);
-    return result;
-}
-
-export function toAlternative(v: _val): undefined | Alternative {
-    let result: undefined | Alternative;
-    if (_.Record.isRecord<_val, _.Tuple<_val>, _embedded>(v)) {
-        let _tmp0: (null) | undefined;
-        _tmp0 = _.is(v.label, $and) ? null : void 0;
-        if (_tmp0 !== void 0) {
-            if (_.Array.isArray(v[0]) && v[0].length >= 1) {
-                let _tmp1: (NamedPattern) | undefined;
-                _tmp1 = toNamedPattern(v[0][0]);
-                if (_tmp1 !== void 0) {
-                    let _tmp2: (Array<_val>) | undefined;
-                    let _tmp3: (Array<NamedPattern>) | undefined;
-                    _tmp2 = v[0].slice(1);
-                    {
-                        _tmp3 = [];
-                        for (const _tmp4 of _tmp2) {
-                            let _tmp5: (NamedPattern) | undefined;
-                            _tmp5 = toNamedPattern(_tmp4);
-                            if (_tmp5 !== void 0) {_tmp3.push(_tmp5); continue;};
-                            _tmp3 = void 0;
-                            break;
-                        };
-                        if (_tmp3 !== void 0) {result = {"_variant": "and", "pattern": _tmp1, "patterns": _tmp3};};
-                    };
-                };
-            };
-        };
-    };
-    if (result === void 0) {
-        let _tmp6: (Pattern) | undefined;
-        _tmp6 = toPattern(v);
-        if (_tmp6 !== void 0) {result = {"_variant": "Pattern", "value": _tmp6};};
-    };
-    return result;
-}
-
-export function fromAlternative(_v: Alternative): _val {
-    switch (_v._variant) {
         case "and": {
             return _.Record(
                 $and,
@@ -827,6 +777,28 @@ export function fromAtomKind(_v: AtomKind): _val {
     };
 }
 
+export function asNamedAlternative(v: _val): NamedAlternative {
+    let result = toNamedAlternative(v);
+    if (result === void 0) throw new TypeError(`Invalid NamedAlternative: ${_.stringify(v)}`);
+    return result;
+}
+
+export function toNamedAlternative(v: _val): undefined | NamedAlternative {
+    let result: undefined | NamedAlternative;
+    if (_.Array.isArray(v) && v.length === 2) {
+        let _tmp0: (string) | undefined;
+        _tmp0 = typeof v[0] === 'string' ? v[0] : void 0;
+        if (_tmp0 !== void 0) {
+            let _tmp1: (Pattern) | undefined;
+            _tmp1 = toPattern(v[1]);
+            if (_tmp1 !== void 0) {result = {"variantLabel": _tmp0, "pattern": _tmp1};};
+        };
+    };
+    return result;
+}
+
+export function fromNamedAlternative(_v: NamedAlternative): _val {return [_v["variantLabel"], fromPattern(_v["pattern"])];}
+
 export function asNamedSimplePattern(v: _val): NamedSimplePattern {
     let result = toNamedSimplePattern(v);
     if (result === void 0) throw new TypeError(`Invalid NamedSimplePattern: ${_.stringify(v)}`);
diff --git a/implementations/javascript/packages/schema/src/meta.ts b/implementations/javascript/packages/schema/src/meta.ts
index 708c139..8d839b1 100644
--- a/implementations/javascript/packages/schema/src/meta.ts
+++ b/implementations/javascript/packages/schema/src/meta.ts
@@ -1,13 +1,10 @@
 import { is, Position } from '@preserves/core';
 import * as M from './gen/schema';
 import { SchemaSyntaxError } from './error';
-import type { AtomicType } from './compiler/type';
 import { isJsKeyword } from './compiler/jskw';
 
 export * from './gen/schema';
 
-export type Builtin = { type: AtomicType, pattern: M.Alternative };
-
 export type Input = M._val;
 
 export function isValidToken(s: string): boolean {
diff --git a/implementations/javascript/packages/schema/src/reader.ts b/implementations/javascript/packages/schema/src/reader.ts
index b35fb68..fcefdf6 100644
--- a/implementations/javascript/packages/schema/src/reader.ts
+++ b/implementations/javascript/packages/schema/src/reader.ts
@@ -1,5 +1,5 @@
 import { Reader, Annotated, Dictionary, is, peel, preserves, Record, strip, Tuple, Position, position, ReaderOptions, stringify, isCompound, KeyedDictionary } from '@preserves/core';
-import { Input, Pattern, Schema, Alternative, Definition, CompoundPattern, SimplePattern } from './meta';
+import { Input, Pattern, Schema, Definition, CompoundPattern, SimplePattern } from './meta';
 import * as M from './meta';
 import { SchemaSyntaxError } from './error';
 
@@ -71,9 +71,7 @@ export function parseSchema(toplevelTokens: Array<Input>,
     function process(toplevelTokens: Array<Input>): void {
         const toplevelClauses = splitBy(peel(toplevelTokens) as Array<Input>, M.DOT);
         for (const clause of toplevelClauses) {
-            if (!Array.isArray(clause)) {
-                invalidClause(clause);
-            } else if (clause.length >= 2 && is(clause[1], M.EQUALS)) {
+            if (clause.length >= 2 && is(clause[1], M.EQUALS)) {
                 const pos = position(clause[0]);
                 const name = peel(clause[0]);
                 if (typeof name !== 'symbol') invalidClause(clause);
@@ -126,51 +124,45 @@ function namedMustBeSimple(p: Position | null): never {
 }
 
 function parseDefinition(name: symbol, pos: Position | null, body: Array<Input>): Definition {
-    let nextAnonymousAlternativeNumber = 0;
-    function alternativeName([input, p]: readonly [Array<Input>, Alternative])
-    : M.NamedAlternative
+    function alternativeName(input: Array<Input>): M.NamedAlternative
     {
         const n = findName(input) || findName(input[0]);
+        const p = parsePattern(name, input);
         if (n !== false) {
-            return M.NamedAlternative({ variantLabel: n.description!, alternative: p });
+            return M.NamedAlternative({ variantLabel: n.description!, pattern: p });
         }
-        if (p._variant === 'Pattern' &&
-            p.value._variant === 'CompoundPattern' &&
-            p.value.value._variant === 'rec' &&
-            p.value.value.label._variant === 'anonymous' &&
-            p.value.value.label.value._variant === 'SimplePattern' &&
-            p.value.value.label.value.value._variant === 'lit' &&
-            typeof p.value.value.label.value.value.value === 'symbol')
+        if (p._variant === 'CompoundPattern' &&
+            p.value._variant === 'rec' &&
+            p.value.label._variant === 'anonymous' &&
+            p.value.label.value._variant === 'SimplePattern' &&
+            p.value.label.value.value._variant === 'lit' &&
+            typeof p.value.label.value.value.value === 'symbol')
         {
             return M.NamedAlternative({
-                variantLabel: p.value.value.label.value.value.value.description!,
-                alternative: p
+                variantLabel: p.value.label.value.value.value.description!,
+                pattern: p
             });
         }
-        if (p._variant === 'Pattern' &&
-            p.value._variant === 'SimplePattern' &&
-            p.value.value._variant === 'Ref')
+        if (p._variant === 'SimplePattern' &&
+            p.value._variant === 'Ref')
         {
             return M.NamedAlternative({
-                variantLabel: p.value.value.value.name.description!,
-                alternative: p
+                variantLabel: p.value.value.name.description!,
+                pattern: p
             });
         }
-        if (p._variant === 'Pattern' &&
-            p.value._variant === 'SimplePattern' &&
-            p.value.value._variant === 'lit')
+        if (p._variant === 'SimplePattern' &&
+            p.value._variant === 'lit')
         {
-            const s = M.namelike(p.value.value.value);
-            if (s !== void 0) return M.NamedAlternative({ variantLabel: s, alternative: p });
+            const s = M.namelike(p.value.value);
+            if (s !== void 0) return M.NamedAlternative({ variantLabel: s, pattern: p });
         }
-        return M.NamedAlternative({
-            variantLabel: '_anonymous' + nextAnonymousAlternativeNumber++,
-            alternative: p
-        });
+        throw new SchemaSyntaxError(preserves`Name missing for alternative: ${input}`, pos);
     }
 
-    function patternName([input, p]: readonly [Array<Input>, Pattern]) : M.NamedPattern {
+    function patternName(input: Array<Input>): M.NamedPattern {
         const n = findName(input) || findName(input[0]);
+        const p = parsePattern(name, input);
         if (n !== false) {
             if (p._variant !== 'SimplePattern') namedMustBeSimple(position(input[0]));
             return M.NamedPattern.named(M.NamedSimplePattern_({ name: n, pattern: p.value }));
@@ -178,28 +170,32 @@ function parseDefinition(name: symbol, pos: Position | null, body: Array<Input>)
         return M.NamedPattern.anonymous(p);
     }
 
-    // TODO: deal with situation where there's an or of ands, where
-    // the branches of the and are named. The parsing is ambiguous, and
-    // with the current code I think (?) you end up with the same name
-    // attached to the or-branch as to the leftmost and-branch.
+    const andPieces = splitBy(body, M.ANDSYM);
+    const orPieces = splitBy(body, M.ORSYM);
 
-    return parseOp(pos,
-                   body,
-                   M.ORSYM,
-                   p => [p, parseOp(pos,
-                                    p,
-                                    M.ANDSYM,
-                                    p => [p, parsePattern(name, p)] as const,
-                                    (p0, ps) => M.Alternative.and({
-                                        pattern: patternName(p0),
-                                        patterns: ps.map(patternName)
-                                    }),
-                                    p => M.Alternative.Pattern(p[1]))] as const,
-                   (p0, ps) => M.Definition.or({
-                       pattern: alternativeName(p0),
-                       patterns: ps.map(alternativeName)
-                   }),
-                   p => M.Definition.Alternative(p[1]));
+    if (andPieces.length === 0 || orPieces.length === 0) {
+        throw new SchemaSyntaxError(preserves`Invalid Schema clause: ${body}`, pos);
+    }
+
+    if (andPieces.length > 1 && orPieces.length > 1) {
+        throw new SchemaSyntaxError(preserves`Mixed "or" and "and" clause: ${body}`, pos);
+    }
+
+    if (andPieces.length > 1) {
+        return M.Definition.and({
+            pattern: patternName(andPieces[0]),
+            patterns: andPieces.slice(1).map(patternName),
+        });
+    }
+
+    if (orPieces.length > 1) {
+        return M.Definition.or({
+            pattern: alternativeName(orPieces[0]),
+            patterns: orPieces.slice(1).map(alternativeName),
+        });
+    }
+
+    return M.Definition.Pattern(parsePattern(name, orPieces[0]));
 }
 
 function parsePattern(name: symbol, body0: Array<Input>): Pattern {
@@ -348,21 +344,6 @@ function parsePattern(name: symbol, body0: Array<Input>): Pattern {
                        () => M.Pattern.CompoundPattern(parseCompound(body[0])));
 }
 
-function parseOp<Each, Combined>(pos: Position | null,
-                                 body: Array<Input>,
-                                 op: Input,
-                                 each: (p: Array<Input>) => Each,
-                                 combineN: (p0: Each, ps: Array<Each>) => Combined,
-                                 finish1: (p: Each) => Combined): Combined
-{
-    const pieces = splitBy(body, op).map(each);
-    if (pieces.length === 0) {
-        throw new SchemaSyntaxError(
-            preserves`Invalid Schema clause: cannot handle empty ${op}`, pos);
-    }
-    return (pieces.length === 1) ? finish1(pieces[0]) : combineN(pieces[0], pieces.slice(1));
-}
-
 function findName(x: Input): symbol | false {
     if (!Annotated.isAnnotated<never>(x)) return false;
     for (const a0 of x.annotations) {
diff --git a/schema/schema.bin b/schema/schema.bin
index 5f613fb..2c1b1df 100644
--- a/schema/schema.bin
+++ b/schema/schema.bin
@@ -3,6 +3,6 @@ ModulePath
 ModulePath„´łrefµ„łSchema„„łPattern´łorµµ±
SimplePattern´łrefµ„ł
SimplePattern„„µ±CompoundPattern´łrefµ„łCompoundPattern„„„„łVersion´łlit‘„łAtomKind´łorµµ±Boolean´łlitłBoolean„„µ±Float´łlitłFloat„„µ±Double´łlitłDouble„„µ±
SignedInteger´łlitł
SignedInteger„„µ±String´łlitłString„„µ±
 ByteString´łlitł
 ByteString„„µ±Symbol´łlitłSymbol„„„„ł
-Definition´łorµµ±or´łrec´łlitłor„´łtupleµ´łtuple*µ´łnamedłpattern´łrefµ„łNamedAlternative„„„´łnamedłpatterns´łrefµ„łNamedAlternative„„„„„„„µ±Alternative´łrefµ„łAlternative„„„„ł
-ModulePath´łtuple*µ„´łatomłSymbol„„łAlternative´łorµµ±and´łrec´łlitłand„´łtupleµ´łtuple*µ´łnamedłpattern´łrefµ„łNamedPattern„„„´łnamedłpatterns´łrefµ„łNamedPattern„„„„„„„µ±Pattern´łrefµ„łPattern„„„„łDefinitions´łdictof´łatomłSymbol„´łrefµ„ł
-Definition„„łNamedPattern´łorµµ±named´łrefµ„łNamedSimplePattern_„„µ±	anonymous´łrefµ„łPattern„„„„ł
SimplePattern´łorµµ±any´łlitłany„„µ±atom´łrec´łlitłatom„´łtupleµ´łnamedłatomKind´łrefµ„łAtomKind„„„„„„µ±embedded´łrec´łlitłembedded„´łtupleµ„„„„µ±lit´łrec´łlitłlit„´łtupleµ´łnamedłvaluełany„„„„„µ±Ref´łrefµ„łRef„„„„łCompoundPattern´łorµµ±rec´łrec´łlitłrec„´łtupleµ´łnamedłlabel´łrefµ„łNamedPattern„„´łnamedłfields´łrefµ„łNamedPattern„„„„„„µ±tuple´łrec´łlitłtuple„´łtupleµ´łtuple*µ„´łnamedłpatterns´łrefµ„łNamedPattern„„„„„„„µ±tuple*´łrec´łlitłtuple*„´łtupleµ´łtuple*µ„´łnamedłfixed´łrefµ„łNamedPattern„„„´łnamedłvariable´łrefµ„łNamedSimplePattern„„„„„„µ±setof´łrec´łlitłsetof„´łtupleµ´łnamedłpattern´łrefµ„ł
SimplePattern„„„„„„µ±dictof´łrec´łlitłdictof„´łtupleµ´łnamedłkey´łrefµ„ł
SimplePattern„„´łnamedłvalue´łrefµ„ł
SimplePattern„„„„„„µ±dict´łrec´łlitłdict„´łtupleµ´łnamedłentries´łrefµ„łDictionaryEntries„„„„„„„„łEmbeddedTypeName´łorµµ±Ref´łrefµ„łRef„„µ±false´łlit€„„„„łNamedAlternative´łtupleµ´łnamedłvariantLabel´łatomłString„„´łnamedłalternative´łrefµ„łAlternative„„„„łDictionaryEntries´łdictofłany´łrefµ„łNamedSimplePattern„„łNamedSimplePattern´łorµµ±named´łrefµ„łNamedSimplePattern_„„µ±	anonymous´łrefµ„ł
SimplePattern„„„„łNamedSimplePattern_´łrec´łlitłnamed„´łtupleµ´łnamedłname´łatomłSymbol„„´łnamedłpattern´łrefµ„ł
SimplePattern„„„„„„łembeddedType€„„
\ No newline at end of file
+Definition´łorµµ±or´łrec´łlitłor„´łtupleµ´łtuple*µ´łnamedłpattern´łrefµ„łNamedAlternative„„„´łnamedłpatterns´łrefµ„łNamedAlternative„„„„„„„µ±and´łrec´łlitłand„´łtupleµ´łtuple*µ´łnamedłpattern´łrefµ„łNamedPattern„„„´łnamedłpatterns´łrefµ„łNamedPattern„„„„„„„µ±Pattern´łrefµ„łPattern„„„„ł
+ModulePath´łtuple*µ„´łatomłSymbol„„łDefinitions´łdictof´łatomłSymbol„´łrefµ„ł
+Definition„„łNamedPattern´łorµµ±named´łrefµ„łNamedSimplePattern_„„µ±	anonymous´łrefµ„łPattern„„„„ł
SimplePattern´łorµµ±any´łlitłany„„µ±atom´łrec´łlitłatom„´łtupleµ´łnamedłatomKind´łrefµ„łAtomKind„„„„„„µ±embedded´łrec´łlitłembedded„´łtupleµ„„„„µ±lit´łrec´łlitłlit„´łtupleµ´łnamedłvaluełany„„„„„µ±Ref´łrefµ„łRef„„„„łCompoundPattern´łorµµ±rec´łrec´łlitłrec„´łtupleµ´łnamedłlabel´łrefµ„łNamedPattern„„´łnamedłfields´łrefµ„łNamedPattern„„„„„„µ±tuple´łrec´łlitłtuple„´łtupleµ´łtuple*µ„´łnamedłpatterns´łrefµ„łNamedPattern„„„„„„„µ±tuple*´łrec´łlitłtuple*„´łtupleµ´łtuple*µ„´łnamedłfixed´łrefµ„łNamedPattern„„„´łnamedłvariable´łrefµ„łNamedSimplePattern„„„„„„µ±setof´łrec´łlitłsetof„´łtupleµ´łnamedłpattern´łrefµ„ł
SimplePattern„„„„„„µ±dictof´łrec´łlitłdictof„´łtupleµ´łnamedłkey´łrefµ„ł
SimplePattern„„´łnamedłvalue´łrefµ„ł
SimplePattern„„„„„„µ±dict´łrec´łlitłdict„´łtupleµ´łnamedłentries´łrefµ„łDictionaryEntries„„„„„„„„łEmbeddedTypeName´łorµµ±Ref´łrefµ„łRef„„µ±false´łlit€„„„„łNamedAlternative´łtupleµ´łnamedłvariantLabel´łatomłString„„´łnamedłpattern´łrefµ„łPattern„„„„łDictionaryEntries´łdictofłany´łrefµ„łNamedSimplePattern„„łNamedSimplePattern´łorµµ±named´łrefµ„łNamedSimplePattern_„„µ±	anonymous´łrefµ„ł
SimplePattern„„„„łNamedSimplePattern_´łrec´łlitłnamed„´łtupleµ´łnamedłname´łatomłSymbol„„´łnamedłpattern´łrefµ„ł
SimplePattern„„„„„„łembeddedType€„„
\ No newline at end of file
diff --git a/schema/schema.prs b/schema/schema.prs
index 8e7a685..6e4f0b9 100644
--- a/schema/schema.prs
+++ b/schema/schema.prs
@@ -21,15 +21,16 @@ EmbeddedTypeName = Ref / #f.
 
 Definitions = { symbol: Definition ...:... }.
 
-; Pattern / Pattern / ...
-; and the empty pattern is <or []>
-Definition = <or [@pattern NamedAlternative @patterns NamedAlternative ...]> / Alternative .
+Definition =
+  ; Pattern / Pattern / ...
+  / <or [@pattern NamedAlternative @patterns NamedAlternative ...]>
 
-NamedAlternative = [@variantLabel string @alternative Alternative].
+  ; Pattern & Pattern & ...
+  / <and [@pattern NamedPattern @patterns NamedPattern ...]>
 
-; Pattern & Pattern & ...
-; and the universal pattern, "any", is <and []>
-Alternative = <and [@pattern NamedPattern @patterns NamedPattern ...]> / Pattern .
+  ; Pattern
+  / Pattern
+.
 
 Pattern = SimplePattern / CompoundPattern .
 
@@ -76,6 +77,8 @@ DictionaryEntries = { any: NamedSimplePattern ...:... }.
 
 AtomKind = =Boolean / =Float / =Double / =SignedInteger / =String / =ByteString / =Symbol .
 
+NamedAlternative = [@variantLabel string @pattern Pattern].
+
 NamedSimplePattern = @named NamedSimplePattern_ / @anonymous SimplePattern .
 NamedPattern = @named NamedSimplePattern_ / @anonymous Pattern .