Chapter 17b: Syntax Sugar

Co-authored-by: Jun Kawasaki <jun784@gmail.com>

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diff --git a/docs/chapter17b/17-grammar.ja.md b/docs/chapter17b/17-grammar.ja.md
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+# 第17b章の文法
+
+[English](17-grammar.md) | 日本語
+
+```antlrv4
+grammar SimpleLanguage;
+
+// Name lookup, assignable operands, type compatibility, and access permissions
+// are checked by the compiler in addition to these syntax rules.
+program : statement* EOF ;
+
+block : '{' statement* '}' ;
+
+statement
+    : block
+    | returnStatement
+    | ifStatement
+    | whileStatement
+    | forStatement
+    | breakStatement
+    | continueStatement
+    | structDeclaration
+    | declaration ';'
+    | assignment ';'
+    | ';'
+    ;
+
+returnStatement   : 'return' assignment ';' ;
+ifStatement       : 'if' '(' assignment ')' statement ('else' statement)? ;
+whileStatement    : 'while' '(' assignment ')' statement ;
+breakStatement    : 'break' ';' ;
+continueStatement : 'continue' ';' ;
+
+forStatement
+    : 'for' '(' (declaration | assignment)? ';' assignment? ';' assignment? ')' statement
+    ;
+
+structDeclaration : 'struct' IDENTIFIER block ';' ;
+
+declaration : declarationType binding (',' binding)* ;
+declarationType : type | 'var' | 'val' ;
+binding : bindingModifier? IDENTIFIER ('=' initializer)? ;
+bindingModifier : '!' | '~' ;
+initializer : assignment ;
+
+// The prefix qualifies the named struct reference, not an enclosing array.
+// Each [] / [~] suffix qualifies its own array layer. ? requires a reference.
+type
+    : primitiveType typeSuffix*
+    | accessModifier? typeName typeSuffix*
+    ;
+accessModifier : '!' | '~' ;
+typeSuffix : '?' | '[]' | '[~]' ;
+typeName : IDENTIFIER ;
+
+primitiveType
+    : 'int' | 'i8' | 'i16' | 'i32' | 'i64'
+    | 'u1' | 'u8' | 'u16' | 'u32' | 'byte' | 'bool'
+    | 'flt' | 'f32' | 'f64'
+    ;
+
+assignment : expression (assignmentOperator assignment)? ;
+assignmentOperator
+    : '=' | '+=' | '-=' | '*=' | '/=' | '&=' | '|=' | '^='
+    | '<<=' | '>>=' | '>>>='
+    ;
+
+expression : bitwiseExpression ('?' assignment (':' assignment)?)? ;
+
+bitwiseExpression
+    : comparisonExpression (('&' | '|' | '^') comparisonExpression)*
+    ;
+
+comparisonExpression
+    : shiftExpression (('==' | '!=' | '<' | '<=' | '>' | '>=') shiftExpression)*
+    ;
+
+shiftExpression
+    : additiveExpression (('<<' | '>>' | '>>>') additiveExpression)*
+    ;
+
+additiveExpression
+    : multiplicativeExpression (('+' | '-') multiplicativeExpression)*
+    ;
+
+multiplicativeExpression
+    : unaryExpression (('*' | '/') unaryExpression)*
+    ;
+
+unaryExpression
+    : ('-' | '!') unaryExpression
+    | updateOperator IDENTIFIER
+    | postfixExpression
+    ;
+
+// Prefix updates require a local name; postfix updates also allow fields
+// and array elements. All updates require an assignable operand.
+updateOperator : '++' | '--' ;
+postfixExpression : primaryExpression postfixSuffix* updateOperator? ;
+postfixSuffix : '.' IDENTIFIER | '[' assignment ']' | '#' ;
+
+primaryExpression
+    : INTEGER_LITERAL
+    | FLOAT_LITERAL
+    | 'true'
+    | 'false'
+    | 'null'
+    | IDENTIFIER
+    | '(' assignment ')'
+    | newExpression
+    ;
+
+// Struct initialization uses a block; array allocation supplies a length.
+newExpression : 'new' type ('[' assignment ']' | block)? ;
+
+INTEGER_LITERAL : '0' | [1-9] DIGIT* ;
+FLOAT_LITERAL : DIGIT+ ('.' DIGIT* ('e' DIGIT+)? | 'e' DIGIT+) ;
+IDENTIFIER : NON_DIGIT (NON_DIGIT | DIGIT)* ;
+fragment NON_DIGIT : [a-zA-Z_] ;
+fragment DIGIT : [0-9] ;
+WHITESPACE : [ \t\r\n]+ -> skip ;
+LINE_COMMENT : '//' ~[\r\n]* -> skip ;
+```
diff --git a/docs/chapter17b/17-grammar.md b/docs/chapter17b/17-grammar.md
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+# Grammar for Chapter 17b
+
+English | [日本語](17-grammar.ja.md)
+
+```antlrv4
+grammar SimpleLanguage;
+
+// Name lookup, assignable operands, type compatibility, and access permissions
+// are checked by the compiler in addition to these syntax rules.
+program : statement* EOF ;
+
+block : '{' statement* '}' ;
+
+statement
+    : block
+    | returnStatement
+    | ifStatement
+    | whileStatement
+    | forStatement
+    | breakStatement
+    | continueStatement
+    | structDeclaration
+    | declaration ';'
+    | assignment ';'
+    | ';'
+    ;
+
+returnStatement   : 'return' assignment ';' ;
+ifStatement       : 'if' '(' assignment ')' statement ('else' statement)? ;
+whileStatement    : 'while' '(' assignment ')' statement ;
+breakStatement    : 'break' ';' ;
+continueStatement : 'continue' ';' ;
+
+forStatement
+    : 'for' '(' (declaration | assignment)? ';' assignment? ';' assignment? ')' statement
+    ;
+
+structDeclaration : 'struct' IDENTIFIER block ';' ;
+
+declaration : declarationType binding (',' binding)* ;
+declarationType : type | 'var' | 'val' ;
+binding : bindingModifier? IDENTIFIER ('=' initializer)? ;
+bindingModifier : '!' | '~' ;
+initializer : assignment ;
+
+// The prefix qualifies the named struct reference, not an enclosing array.
+// Each [] / [~] suffix qualifies its own array layer. ? requires a reference.
+type
+    : primitiveType typeSuffix*
+    | accessModifier? typeName typeSuffix*
+    ;
+accessModifier : '!' | '~' ;
+typeSuffix : '?' | '[]' | '[~]' ;
+typeName : IDENTIFIER ;
+
+primitiveType
+    : 'int' | 'i8' | 'i16' | 'i32' | 'i64'
+    | 'u1' | 'u8' | 'u16' | 'u32' | 'byte' | 'bool'
+    | 'flt' | 'f32' | 'f64'
+    ;
+
+assignment : expression (assignmentOperator assignment)? ;
+assignmentOperator
+    : '=' | '+=' | '-=' | '*=' | '/=' | '&=' | '|=' | '^='
+    | '<<=' | '>>=' | '>>>='
+    ;
+
+expression : bitwiseExpression ('?' assignment (':' assignment)?)? ;
+
+bitwiseExpression
+    : comparisonExpression (('&' | '|' | '^') comparisonExpression)*
+    ;
+
+comparisonExpression
+    : shiftExpression (('==' | '!=' | '<' | '<=' | '>' | '>=') shiftExpression)*
+    ;
+
+shiftExpression
+    : additiveExpression (('<<' | '>>' | '>>>') additiveExpression)*
+    ;
+
+additiveExpression
+    : multiplicativeExpression (('+' | '-') multiplicativeExpression)*
+    ;
+
+multiplicativeExpression
+    : unaryExpression (('*' | '/') unaryExpression)*
+    ;
+
+unaryExpression
+    : ('-' | '!') unaryExpression
+    | updateOperator IDENTIFIER
+    | postfixExpression
+    ;
+
+// Prefix updates require a local name; postfix updates also allow fields
+// and array elements. All updates require an assignable operand.
+updateOperator : '++' | '--' ;
+postfixExpression : primaryExpression postfixSuffix* updateOperator? ;
+postfixSuffix : '.' IDENTIFIER | '[' assignment ']' | '#' ;
+
+primaryExpression
+    : INTEGER_LITERAL
+    | FLOAT_LITERAL
+    | 'true'
+    | 'false'
+    | 'null'
+    | IDENTIFIER
+    | '(' assignment ')'
+    | newExpression
+    ;
+
+// Struct initialization uses a block; array allocation supplies a length.
+newExpression : 'new' type ('[' assignment ']' | block)? ;
+
+INTEGER_LITERAL : '0' | [1-9] DIGIT* ;
+FLOAT_LITERAL : DIGIT+ ('.' DIGIT* ('e' DIGIT+)? | 'e' DIGIT+) ;
+IDENTIFIER : NON_DIGIT (NON_DIGIT | DIGIT)* ;
+fragment NON_DIGIT : [a-zA-Z_] ;
+fragment DIGIT : [0-9] ;
+WHITESPACE : [ \t\r\n]+ -> skip ;
+LINE_COMMENT : '//' ~[\r\n]* -> skip ;
+```
diff --git a/docs/chapter17b/Makefile b/docs/chapter17b/Makefile
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+GV := $(wildcard *.gv)
+SVG := $(patsubst %.gv,%.svg,$(GV))
+
+.PHONY: all
+all: $(SVG)
+
+%.svg: %.gv
+	dot -Tsvg $< > $@
+
+.PHONY: clean
+clean:
+	@rm -f $(SVG)
diff --git a/docs/chapter17b/README.ja.md b/docs/chapter17b/README.ja.md
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+# 第17b章: 糖衣構文
+
+[English](README.md) | 日本語
+
+[前: 第17a章](../chapter17a/README.ja.md) |
+[次: 第18章](../chapter18/README.ja.md)
+
+この文書は [原文](README.md) の日本語訳です。
+
+この章の[完全な言語文法](17-grammar.ja.md)はこちらです。
+
+## 目次
+
+1. [前置・後置インクリメント](#前置後置インクリメント)
+2. [複合代入](#複合代入)
+3. [var/val](#var-と-val)
+4. [三項演算](#三項演算)
+5. [for ループ](#for-ループ)
+
+第17a章では、代入で確認する権限を確立しました。この章ではその権限を変えずに、代入と制御フローを短く書く方法を追加します。その後、第18章で関数と呼び出しを導入します。
+
+## 前置・後置インクリメント
+
+`arg++` と `arg--` を、通常の意味で許します。値を更新し、式の値は更新前の値になります。最長一致を使うので、`arg---arg` は `(arg--)-arg` としてパースします。
+
+`s.fld++` と `ary[idx]++`、それらの `--` 版も許します。
+
+前置インクリメントは、今のところ識別子についてだけ許します。例は `--pc` です。
+
+## 複合代入
+
+後置インクリメントと同じ方向で、局所変数への `op=` 代入も、ほかの言語に似た意味論で許すようになります。サポートする演算子は `+=`、`-=`、`*=`、`/=`、`&=`、`|=`、`^=`、`<<=`、`>>=`、`>>>=` です。ビット演算とシフトの代入には整数オペランドが必要です。`>>=` は符号を保持し、`>>>=` はゼロを入れます。代入は右辺を1回評価し、結果を変数の型に狭めて格納し、その格納値を式の結果とします。代入は、`x |= y <<= 2` のように右から左に結合します。
+
+## var と val
+
+`var` と `val` は変数を宣言し、その型を推論します。`var` は再代入可能な束縛、`val` は固定の束縛を推論します。両方とも初期化式のアクセス権限を保ちます。どちらも、書き込み可能なオブジェクトを読み取り専用にはしません。この2つの独立した権限は[第17a章](../chapter17a/README.ja.md)から来ています。
+
+```cpp
+struct Point { int x; };
+val p = new Point; // Fixed binding to a writable new object
+p.x = 3;           // Allowed
+// p = new Point;  // Error: fixed binding
+Point view = p;    // Explicit read-only view
+var q = view;      // Reassignable binding, still read-only access
+// q.x = 4;        // Error: cannot restore write permission by inference
+```
+
+型推論には初期化子が必須です。プリミティブでは広い数値型（`int` または `flt`）を推論し、参照ではアクセス権限を保持します。再代入可能な推論された参照は、後で空の値を保持できるように null を許容します。明示的な型は、宣言された幅と null 許容性を維持します。関数パラメータには依然として明示的な型が必要です。
+
+## 三項演算
+
+`pred ? e_true : e_false` を許します。`pred ? e_true` も許し、この場合の false の結果は true の結果のゼロ型版です。
+
+## for ループ
+
+C/C++ 形式の `for` ループを許します。
+
+`for( init; test; next ) body`
+
+例:
+
+```cpp
+int sum=0;
+for( int i=0; i<arg; i++ )
+    sum += i;
+return sum;
+```
+
+`init`、`test`、`next` のどれも空にできます。`init` には新しい変数の宣言を許し、そのスコープは `for` 式に限定されます。
+
+```cpp
+int sum=0;
+for( int i=0; i<arg; i++ )
+    sum += i;
+return i; // ERROR: Undefined name 'i'
+```
+
+誤った `find` 呼び出し:
+
+```cpp
+for( int i=0; i<ary#; i++ )
+  if( ary[i]==e )
+    break;
+do_stuff(i); // ERROR: undefined name 'i'
+```
+
+`find` 呼び出しの例:
+
+```cpp
+for( int i=0; i<ary#; i++ )
+  if( ary[i]==e )
+    return i;
+return -1;
+```
diff --git a/docs/chapter17b/README.md b/docs/chapter17b/README.md
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+# Chapter 17b: Syntax Sugar
+
+English | [日本語](README.ja.md)
+
+[Previous: Chapter 17a](../chapter17a/README.md) |
+[Next: Chapter 18](../chapter18/README.md)
+
+
+Here is the [complete language grammar](17-grammar.md) for this chapter.
+
+## Table of Contents
+
+1. [Pre/Post-increment](#prepost-increment)
+2. [Operator assignment](#operator-assignment)
+3. [var/val](#var--val)
+4. [Trinary](#trinary)
+5. [For Loops](#for-loops)
+
+Chapter 17a established the permissions checked by assignments. This chapter
+adds shorter ways to write assignments and control flow without changing those
+permissions. Chapter 18 then introduces functions and calls.
+
+## Pre/Post-increment
+
+Allow `arg++` and `arg--` with the usual meanings; the value is updated and the
+expression is the pre-update value.  Greedy match is used so `arg---arg` parses
+as `(arg--)-arg`.
+
+Also allows `s.fld++` and `ary[idx]++`, and their `--` variants.
+
+Allow pre-increment for identifiers only, for now: `--pc`.
+
+
+## Operator assignment
+
+Along the same lines as post-increment, we now allow `op=` assignment
+on local variables with semantics similar to other languages. The supported
+operators are `+=`, `-=`, `*=`, `/=`, `&=`, `|=`, `^=`, `<<=`, `>>=`, and `>>>=`.
+Bitwise and shift assignments require integer operands; `>>=` preserves the sign
+while `>>>=` shifts in zeros. The assignment evaluates its right-hand side once,
+stores the result narrowed to the variable's type, and yields that stored value.
+Assignments associate right-to-left, as in `x |= y <<= 2`.
+
+
+
+## var & val
+
+`var` and `val` declare variables and infer their types; `var` infers a
+reassignable binding while `val` infers a fixed binding.  Both preserve access
+permissions from the initializing expression.  Neither makes a writable object
+read-only.  The two independent permissions come from [Chapter
+17a](../chapter17a/README.md).
+
+```cpp
+struct Point { int x; };
+val p = new Point; // Fixed binding to a writable new object
+p.x = 3;           // Allowed
+// p = new Point;  // Error: fixed binding
+Point view = p;    // Explicit read-only view
+var q = view;      // Reassignable binding, still read-only access
+// q.x = 4;        // Error: cannot restore write permission by inference
+```
+
+The initializer is required for type inference.  Primitives infer their broad
+numeric type (`int` or `flt`); references retain their access permissions.  A
+reassignable inferred reference allows null so it can later hold the empty
+value.  Explicit types retain their declared width and nullability.  Function
+parameters still require explicit types.
+
+## Trinary
+
+Allow `pred ? e_true : e_false`.  Also allow `pred ? e_true`, where the false result
+is the zero type version of the true result.
+
+
+## For Loops
+
+Allow C/C++ style `for` loops:
+
+`for( init; test; next ) body`
+
+Example:
+
+```cpp
+int sum=0;
+for( int i=0; i<arg; i++ )
+    sum += i;
+return sum;
+```
+
+Any of `init`, `test` and `next` can be empty.  `init` allows for declaration
+of a new variable, with scope limited to the `for` expression.
+
+```cpp
+int sum=0;
+for( int i=0; i<arg; i++ )
+    sum += i;
+return i; // ERROR: Undefined name 'i'
+```
+
+A broken `find` call:
+```cpp
+for( int i=0; i<ary#; i++ )
+  if( ary[i]==e )
+    break;
+do_stuff(i); // ERROR: undefined name 'i'
+```
+
+An example `find` call:
+```cpp
+for( int i=0; i<ary#; i++ )
+  if( ary[i]==e )
+    return i;
+return -1;
+```