From 107ce1646e24b0d30f7fc42e831a7e5f03daecc3 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sat, 30 Sep 2023 11:01:22 +0100
Subject: Parse when expressions

---
 .../java/org/shedlang/compiler/parser/Parser.java  | 41 +++++++++++++++++++++-
 .../org/shedlang/compiler/parser/TokenType.java    |  2 ++
 .../org/shedlang/compiler/parser/Tokeniser.java    |  2 ++
 3 files changed, 44 insertions(+), 1 deletion(-)

(limited to 'src/main/java/org/shedlang/compiler/parser')

diff --git a/src/main/java/org/shedlang/compiler/parser/Parser.java b/src/main/java/org/shedlang/compiler/parser/Parser.java
index 84900688..71490933 100644
--- a/src/main/java/org/shedlang/compiler/parser/Parser.java
+++ b/src/main/java/org/shedlang/compiler/parser/Parser.java
@@ -540,6 +540,8 @@ public class Parser {
             case KEYWORD_IF -> parseIf(tokens);
 
             case KEYWORD_FALSE, KEYWORD_TRUE -> parseBoolLiteral(tokens);
+            
+            case KEYWORD_WHEN -> parseWhen(tokens);
 
             case STRING -> parseStringLiteral(tokens);
 
@@ -812,7 +814,6 @@ public class Parser {
         return new UntypedTupleTypeNode(elements, source);
     }
 
-
     private static UntypedTypeLevelReferenceNode parseTypeLevelReference(TokenIterator<TokenType> tokens) {
         var start = tokens.position();
 
@@ -824,6 +825,44 @@ public class Parser {
         return new UntypedTypeLevelReferenceNode(name, source);
     }
 
+    private static UntypedExpressionNode parseWhen(TokenIterator<TokenType> tokens) {
+        var start = tokens.position();
+
+        tokens.skip(TokenType.KEYWORD_WHEN);
+
+        tokens.skip(TokenType.SYMBOL_PAREN_OPEN);
+        var expression = parseTopLevelExpression(tokens);
+        tokens.skip(TokenType.SYMBOL_PAREN_CLOSE);
+
+        tokens.skip(TokenType.SYMBOL_BRACE_OPEN);
+        var cases = parseMany(
+            () -> tokens.isNext(TokenType.SYMBOL_BRACE_CLOSE),
+            () -> parseWhenCase(tokens),
+            () -> true
+        );
+        tokens.skip(TokenType.SYMBOL_BRACE_CLOSE);
+
+        var end = tokens.position();
+        var source = start.to(end);
+
+        return new UntypedWhenNode(expression, cases, source);
+    }
+
+    private static UntypedWhenCaseNode parseWhenCase(TokenIterator<TokenType> tokens) {
+        var start = tokens.position();
+
+        tokens.skip(TokenType.KEYWORD_IS);
+
+        var caseType = parseTopLevelTypeLevelExpression(tokens);
+
+        var body = parseBlock(tokens);
+
+        var end = tokens.position();
+        var source = start.to(end);
+
+        return new UntypedWhenCaseNode(caseType, body, source);
+    }
+
     private static UntypedFunctionStatementNode parseWhile(
         TokenIterator<TokenType> tokens
     ) {
diff --git a/src/main/java/org/shedlang/compiler/parser/TokenType.java b/src/main/java/org/shedlang/compiler/parser/TokenType.java
index 9c8183dc..e2350ae2 100644
--- a/src/main/java/org/shedlang/compiler/parser/TokenType.java
+++ b/src/main/java/org/shedlang/compiler/parser/TokenType.java
@@ -14,12 +14,14 @@ public enum TokenType {
     KEYWORD_FALSE,
     KEYWORD_FUN,
     KEYWORD_IF,
+    KEYWORD_IS,
     KEYWORD_RETURN,
     KEYWORD_STRUCT,
     KEYWORD_SUMTYPE,
     KEYWORD_TRUE,
     KEYWORD_VAL,
     KEYWORD_VAR,
+    KEYWORD_WHEN,
     KEYWORD_WHILE,
 
     SYMBOL_BANG,
diff --git a/src/main/java/org/shedlang/compiler/parser/Tokeniser.java b/src/main/java/org/shedlang/compiler/parser/Tokeniser.java
index 7659d717..e7f04189 100644
--- a/src/main/java/org/shedlang/compiler/parser/Tokeniser.java
+++ b/src/main/java/org/shedlang/compiler/parser/Tokeniser.java
@@ -18,12 +18,14 @@ public class Tokeniser {
         Map.entry("false", TokenType.KEYWORD_FALSE),
         Map.entry("fun", TokenType.KEYWORD_FUN),
         Map.entry("if", TokenType.KEYWORD_IF),
+        Map.entry("is", TokenType.KEYWORD_IS),
         Map.entry("return", TokenType.KEYWORD_RETURN),
         Map.entry("struct", TokenType.KEYWORD_STRUCT),
         Map.entry("sumtype", TokenType.KEYWORD_SUMTYPE),
         Map.entry("true", TokenType.KEYWORD_TRUE),
         Map.entry("val", TokenType.KEYWORD_VAL),
         Map.entry("var", TokenType.KEYWORD_VAR),
+        Map.entry("when", TokenType.KEYWORD_WHEN),
         Map.entry("while", TokenType.KEYWORD_WHILE)
     );
 
-- 
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