Destructuring & patterns

nois-lang · Jun 11, 2023 · 85c6e53 · 85c6e53
1 parent 807c37f
commit 85c6e53
Show file tree

Hide file tree

Showing 5 changed files with 107 additions and 30 deletions.
diff --git a/data/features.no b/data/features.no
@@ -36,16 +36,19 @@ fn foo(): Unit {
     // alternative syntax
     Vec2.fmt(vec)
 
-    // TODO: method call syntax for ambiguous methods
-    // Vec2.Display.fmt(vec)
+    // method call syntax for ambiguous methods
+    Vec2.Display.fmt(vec)
 
     // if
     let a = if True { 4 } else { 2 + 6 }
 
     // TODO: loops
 
-    // TODO: destructuring
-    // let Vec { x } = vec
+    // destructuring
+    let Vec(x) = vec
+
+    // destructuring alias
+    let Vec(x: b) = vec
 
     // TODO: match
     // let b = match 4 {

diff --git a/nois.bnf b/nois.bnf
@@ -2,7 +2,7 @@ module              ::= statement*
                     ;
 statement           ::= var-def | fn-def | kind-def | impl-def | type-def | return-stmt | expr
                     ;
-  var-def           ::= LET-KEYWORD IDENTIFIER type-annot? EQUALS expr
+  var-def           ::= LET-KEYWORD pattern type-annot? EQUALS expr
                     ;
   fn-def            ::= FN-KEYWORD type-expr params? type-annot? block?
                     ;
@@ -78,7 +78,7 @@ statement           ::= var-def | fn-def | kind-def | impl-def | type-def | retu
                     ;
     params          ::= O-PAREN (param (COMMA param)*)? COMMA? C-PAREN
                     ;
-        param       ::= IDENTIFIER type-annot?
+        param       ::= pattern type-annot?
                     ;
 block               ::= O-BRACE statement* C-BRACE
                     ;
@@ -90,5 +90,13 @@ type-annot          ::= COLON type-expr
                     ;
 if-expr             ::= IF-KEYWORD expr block (ELSE-KEYWORD block)?
                     ;
-hole                ::= UNDERSCORE
+pattern             ::= con-pattern | IDENTIFIER | hole
+                    ;
+  con-pattern       ::= IDENTIFIER con-pattern-params
+                    ;
+  con-pattern-params::= O-PAREN (field-pattern (COMMA field-pattern)*)? COMMA? C-PAREN
+                    ;
+    field-pattern   ::= IDENTIFIER (COLON pattern)? | spread-op
+                    ;
+  hole              ::= UNDERSCORE
                     ;
diff --git a/src/parser/parser-fns.ts b/src/parser/parser-fns.ts
@@ -54,12 +54,12 @@ const parseStatement = (parser: Parser): void => {
 }
 
 /**
- * var-def ::= LET-KEYWORD IDENTIFIER type-annot? EQUALS expr
+ * var-def ::= LET-KEYWORD pattern type-annot? EQUALS expr
  */
 const parseVarDef = (parser: Parser): void => {
     const mark = parser.open()
     parser.expect('let-keyword')
-    parser.expect('identifier')
+    parsePattern(parser)
     if (parser.at('colon')) {
         parseTypeAnnot(parser)
     }
@@ -357,6 +357,13 @@ const parsePrefixOp = (parser: Parser): void => {
     parser.close(mark, 'prefix-op')
 }
 
+const parseSpreadOp = (parser: Parser): void => {
+    const mark = parser.open()
+    parser.expect('period')
+    parser.expect('period')
+    parser.close(mark, 'spread-op')
+}
+
 /**
  * postfix-op ::= call-op
  */
@@ -484,7 +491,7 @@ const parseParams = (parser: Parser): void => {
  */
 const parseParam = (parser: Parser): void => {
     const mark = parser.open()
-    parser.expect('identifier')
+    parsePattern(parser)
     if (parser.at('colon')) {
         parseTypeAnnot(parser)
     }
@@ -560,6 +567,74 @@ const parseIfExpr = (parser: Parser): void => {
     parser.close(mark, 'if-expr')
 }
 
+/**
+ * pattern ::= con-pattern | IDENTIFIER | hole
+ */
+const parsePattern = (parser: Parser): void => {
+    const mark = parser.open()
+    if (parser.at('identifier') && parser.nth(1) === 'o-paren') {
+        parseConPattern(parser)
+    } else if (parser.at('identifier')) {
+        parser.expect('identifier')
+    } else if (parser.at('underscore')) {
+        parseHole(parser)
+    } else {
+        parser.advanceWithError('expected pattern')
+    }
+    parser.close(mark, 'pattern')
+}
+
+/**
+ * con-pattern ::= IDENTIFIER con-pattern-params
+ */
+const parseConPattern = (parser: Parser): void => {
+    const mark = parser.open()
+    parser.expect('identifier')
+    parseConPatternParams(parser)
+    parser.close(mark, 'con-pattern')
+}
+
+/**
+ * con-pattern-params::= O-PAREN (field-pattern (COMMA field-pattern)*)? COMMA? C-PAREN
+ */
+const parseConPatternParams = (parser: Parser): void => {
+    const mark = parser.open()
+    parser.expect('o-paren')
+    while (!parser.at('c-paren') && !parser.eof()) {
+        parseFieldPattern(parser)
+        if (!parser.at('c-paren')) {
+            parser.expect('comma')
+        }
+    }
+    parser.expect('c-paren')
+    parser.close(mark, 'con-pattern-params')
+}
+
+/**
+ * field-pattern ::= IDENTIFIER (COLON pattern) | spread-op
+ */
+const parseFieldPattern = (parser: Parser): void => {
+    const mark = parser.open()
+    if (parser.at('identifier')) {
+        parser.expect('identifier')
+        if (parser.consume('colon')) {
+            parsePattern(parser)
+        }
+    } else if (parser.at('period')) {
+        parseSpreadOp(parser)
+    }
+    parser.close(mark, 'field-pattern')
+}
+
+/**
+ * hole ::= UNDERSCORE
+ */
+const parseHole = (parser: Parser): void => {
+    const mark = parser.open()
+    parser.expect('underscore')
+    parser.close(mark, 'hole')
+}
+
 const parseTodo = (parser: Parser): void => {
     parser.advanceWithError('todo')
 }
diff --git a/src/parser/parser.spec.ts b/src/parser/parser.spec.ts
@@ -33,17 +33,11 @@ describe('parser', () => {
     describe('parse var-def', () => {
         it('miss identifier', () => {
             const { errors } = parse('let = 4')
-            expect(errors.length).toEqual(1)
+            expect(errors.length).toEqual(2)
             expect(errors[0]).toEqual({
-                'expected': ['identifier'],
-                'got': {
-                    'kind': 'equals',
-                    'location': {
-                        'end': 4,
-                        'start': 4
-                    },
-                    'value': '='
-                }
+                'expected': [],
+                'got': { 'kind': 'equals', 'location': { 'end': 4, 'start': 4 }, 'value': '=' },
+                'message': 'expected pattern'
             })
         })
     })
@@ -64,23 +58,15 @@ describe('parser', () => {
                                         {
                                             'block': [
                                                 { 'o-brace': '{' },
-                                                {
-                                                    'statement': [{
-                                                        'expr': [{ 'sub-expr': [{ 'operand': [{ 'identifier': 'b' }] }] }]
-                                                    }]
-                                                },
+                                                { 'statement': [{ 'expr': [{ 'sub-expr': [{ 'operand': [{ 'identifier': 'b' }] }] }] }] },
                                                 { 'c-brace': '}' }
                                             ]
                                         },
                                         { 'else-keyword': 'else' },
                                         {
                                             'block': [
                                                 { 'o-brace': '{' },
-                                                {
-                                                    'statement': [{
-                                                        'expr': [{ 'sub-expr': [{ 'operand': [{ 'identifier': 'c' }] }] }]
-                                                    }]
-                                                },
+                                                { 'statement': [{ 'expr': [{ 'sub-expr': [{ 'operand': [{ 'identifier': 'c' }] }] }] }] },
                                                 { 'c-brace': '}' }
                                             ]
                                         }

diff --git a/src/parser/parser.ts b/src/parser/parser.ts
@@ -53,6 +53,11 @@ export const treeKinds = <const>[
     'type-expr',
     'type-params',
     'if-expr',
+    'pattern',
+    'con-pattern',
+    'con-pattern-params',
+    'field-pattern',
+    'hole',
 ]
 export type TreeKind = typeof treeKinds[number]