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pattern-matching Expert skill for implementing pattern matching including exhaustiveness checking, decision tree compilation, and efficient match dispatch code generation.
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2 arquivos name pattern-matching description Expert skill for implementing pattern matching including exhaustiveness checking, decision tree compilation, and efficient match dispatch code generation. allowed-tools Read, Write, Edit, Bash, Glob, Grep graph {"domains":["domain:software-engineering"],"specializations":["specialization:programming-languages"],"skillAreas":["skill-area:compiler-implementation","skill-area:language-design"],"roles":["role:backend-engineer"]}
Pattern Matching Skill
Implement pattern matching for programming languages including exhaustiveness checking, usefulness analysis, and efficient compilation to decision trees.
Capabilities
Parse pattern syntax (constructor, wildcard, binding, literals)
Implement exhaustiveness and usefulness checking
Compile patterns to decision trees
Implement guard clause handling
Design or-patterns and as-patterns
Implement nested pattern matching
Optimize pattern match coverage
Generate efficient match dispatch code
Usage
Invoke this skill when you need to:
Add pattern matching to a language
Implement exhaustiveness checking
Compile patterns efficiently
Handle complex pattern features
Inputs
patternTypes array Yes Types of patterns to support targetLanguage string Yes Language for implementation compilationStrategy string No Strategy (decision-tree, backtracking) features array No Advanced features to implement
Pattern Types {
"patternTypes" : [
"wildcard" ,
"variable" ,
"literal" ,
"constructor" ,
"tuple" ,
"record" ,
"list" ,
"or-pattern" ,
"as-pattern" ,
"guard"
]
}
Feature Options {
"features" : [
"exhaustiveness-checking" ,
"usefulness-checking" ,
"decision-tree-compilation" ,
"guard-clauses" ,
"nested-patterns" ,
"view-patterns" ,
"active-patterns"
]
}
Output Structure pattern-matching/
├── syntax/
│ ├── pattern.grammar # Pattern syntax
│ └── match-expr.grammar # Match expression syntax
├── analysis/
│ ├── exhaustiveness.ts # Exhaustiveness checker
│ ├── usefulness.ts # Usefulness/redundancy checker
│ └── pattern-types.ts # Pattern type inference
├── compilation/
│ ├── decision-tree.ts # Decision tree builder
│ ├── code-generator.ts # Code generation
│ └── optimizer.ts # Pattern optimization
├── runtime/
│ ├── matcher.ts # Runtime matching (interpreter)
│ └── guards.ts # Guard evaluation
└── tests/
├── exhaustiveness.test.ts
├── compilation.test.ts
└── runtime.test.ts
Pattern Syntax
type Pattern =
| { type : 'wildcard' }
| { type : 'variable' ; name : string }
| { type : 'literal' ; value : Literal }
| { type : 'constructor' ; name : string ; args : Pattern [] }
| { type : 'tuple' ; elements : Pattern [] }
| { type : 'record' ; fields : Map <string , Pattern > }
| { type : 'list' ; elements : Pattern []; rest ?: Pattern }
| { type : 'or' ; patterns : Pattern [] }
| { type : 'as' ; pattern : Pattern ; name : string }
| { type : 'guard' ; pattern : Pattern ; guard : Expr };
interface MatchExpr {
scrutinee : Expr ;
arms : MatchArm [];
}
interface MatchArm {
pattern : Pattern ;
guard ?: Expr ;
body : Expr ;
}
Exhaustiveness Checking
type PatternMatrix = Pattern [][];
function isExhaustive (matrix : PatternMatrix , types : Type []boolean {
if (matrix.length === 0 ) return false ;
if (types.length === 0 ) return true ;
const firstCol = matrix.map (row =>0 ]);
const sigma = getConstructorSignature (types[0 ]);
if (sigma.isComplete (firstCol)) {
return sigma.constructors .every (ctor =>isExhaustive (specialize (matrix, ctor), specializationTypes (types, ctor))
);
} else {
return isExhaustive (defaultMatrix (matrix), types.slice (1 ));
}
}
function findUncoveredCase (matrix : PatternMatrix , types : Type []Pattern [] | null {
if (matrix.length === 0 ) {
return types.map (generateWildcard);
}
if (types.length === 0 ) return null ;
const sigma = getConstructorSignature (types[0 ]);
const firstCol = matrix.map (row =>0 ]);
if (sigma.isComplete (firstCol)) {
for (const ctor of sigma.constructors ) {
const witness = findUncoveredCase (
specialize (matrix, ctor),
specializationTypes (types, ctor)
);
if (witness) {
return [applyConstructor (ctor, witness.slice (0 , ctor.arity )), ...witness.slice (ctor.arity )];
}
}
return null ;
} else {
const missing = sigma.constructors .find (c =>some (p =>matchesCtor (p, c)));
if (missing) {
return [generatePattern (missing), ...types.slice (1 ).map (generateWildcard)];
}
return findUncoveredCase (defaultMatrix (matrix), types.slice (1 ));
}
}
Decision Tree Compilation
type DecisionTree =
| { type : 'fail' }
| { type : 'leaf' ; bindings : Map <string , Access >; body : Expr }
| { type : 'switch' ; access : Access ; cases : SwitchCase []; default ?: DecisionTree };
interface SwitchCase {
constructor : Constructor ;
tree : DecisionTree ;
}
interface Access {
root : string ;
path : AccessStep [];
}
type AccessStep =
| { type : 'field' ; index : number }
| { type : 'deref' };
function compilePatterns (arms : MatchArm [], scrutinee : Access DecisionTree {
if (arms.length === 0 ) return { type : 'fail' };
const column = selectColumn (arms);
const groups = groupByConstructor (arms, column);
if (groups.size === 0 ) {
const bindings = extractBindings (arms[0 ].pattern , scrutinee);
return { type : 'leaf' , bindings, body : arms[0 ].body };
}
const cases : SwitchCase [] = [];
for (const [ctor, ctorArms] of groups) {
const specializedAccess = extendAccess (scrutinee, ctor);
cases.push ({
constructor : ctor,
tree : compilePatterns (specializeArms (ctorArms, ctor), specializedAccess)
});
}
const defaultArms = arms.filter (arm =>isWildcard (arm.pattern , column));
const defaultTree = defaultArms.length > 0
? compilePatterns (defaultArms, scrutinee)
: undefined ;
return { type : 'switch' , access : scrutinee, cases, default : defaultTree };
}
Guard Clause Handling
interface GuardedArm {
pattern : Pattern ;
guard : Expr | null ;
body : Expr ;
}
function exhaustivenessWithGuards (arms : GuardedArm [], types : Type []Warning [] {
const warnings : Warning [] = [];
const unguardedMatrix = arms.map (arm =>pattern ]);
if (!isExhaustive (unguardedMatrix, types)) {
warnings.push ({
type : 'possibly-non-exhaustive' ,
message : 'Match may not be exhaustive (guards present)' ,
suggestion : 'Consider adding a catch-all pattern'
});
}
return warnings;
}
type GuardedTree =
| { type : 'fail' }
| { type : 'guard' ; test : Expr ; success : GuardedTree ; failure : GuardedTree }
| { type : 'leaf' ; bindings : Map <string , Access >; body : Expr }
| { type : 'switch' ; access : Access ; cases : SwitchCase []; default ?: GuardedTree };
Code Generation
function generateCode (tree : DecisionTree , target : CodeTarget Code {
switch (tree.type ) {
case 'fail' :
return target.emitMatchFailure ();
case 'leaf' :
const setup = Array .from (tree.bindings .entries ())
.map (([name, access] ) => target.emitBinding (name, access));
return target.emitBlock ([...setup, target.emitExpr (tree.body )]);
case 'switch' :
return target.emitSwitch (
target.emitAccess (tree.access ),
tree.cases .map (c =>test : target.emitConstructorTest (c.constructor ),
body : generateCode (c.tree , target)
})),
tree.default ? generateCode (tree.default , target) : target.emitMatchFailure ()
);
}
}
function emitRustMatch (tree : DecisionTree string {
}
Or-Patterns and As-Patterns
function expandOrPattern (pattern : Pattern Pattern [] {
if (pattern.type === 'or' ) {
return pattern.patterns .flatMap (expandOrPattern);
}
return [pattern];
}
function handleAsPattern (
pattern : AsPattern ,
access : Access ,
bindings : Map <string , Access >
): void {
bindings.set (pattern.name , access);
extractBindings (pattern.pattern , access, bindings);
}
Workflow
Define pattern syntax - Grammar for patternsImplement pattern parser - Parse patterns to ASTBuild exhaustiveness checker - Matrix-based analysisAdd usefulness checker - Detect redundant patternsImplement decision tree compilation - Efficient matchingGenerate target code - From decision treesHandle guards - Conservative guard analysisWrite tests - Exhaustiveness, compilation, runtime
Best Practices Applied
Conservative exhaustiveness with guards
Informative non-exhaustiveness witnesses
Efficient decision tree compilation
Proper binding extraction order
Support for nested patterns
Clear redundancy warnings
References
Target Processes
pattern-matching-implementation.js
parser-development.js
code-generation-llvm.js
interpreter-implementation.js
