Chapter 3: Variable Declarations

Co-authored-by: Dibyendu Majumdar <mobile@majumdar.org.uk> Co-authored-by: Yichen Yan <oraluben@outlook.com> Co-authored-by: Thalia Archibald <thalia@archibald.dev> Co-authored-by: Tamas Hadhazy <helsgithub15@gmail.com> Co-authored-by: Hsiang-Ying Fu <66062782+fuhsnn@users.noreply.github.com> Co-authored-by: XmiliaH <45106915+XmiliaH@users.noreply.github.com> Co-authored-by: Tamás Hadházy <85063808+Hels15@users.noreply.github.com> Co-authored-by: tannal <tannal2409@gmail.com> Co-authored-by: hadha <helsgithub15@gmail.com> Co-authored-by: godalming123 <68993177+godalming123@users.noreply.github.com> Co-authored-by: RobertObkircher <robert.obkircher@gmail.com>
author: Cliff Click <cliffc@acm.org> 2023-10-01 18:01:54 +0100
committer: Cliff Click <cliffc@acm.org> 2026-10-04 13:30:41 -0700
commit: bafb37e0078950acdf0d0218a977beaf05e0b6ac (patch)
tree: 03ca39c0f3b409b014a0f0659b65e5f3567af140 /docs/chapter03
parent: c9ca49691ac9040eb0459ac6de6c2fe62a347a02 (diff)
download: Simple-bafb37e0078950acdf0d0218a977beaf05e0b6ac.tar.gz
Simple-bafb37e0078950acdf0d0218a977beaf05e0b6ac.zip
16 files changed, 893 insertions, 0 deletions
diff --git a/docs/chapter03/03-grammar.md b/docs/chapter03/03-grammar.md
new file mode 100644
index 00000000..1d36b532
--- /dev/null
+++ b/docs/chapter03/03-grammar.md
@@ -0,0 +1,68 @@
+# Grammar for Chapter 1
+
+```antlrv4
+grammar SimpleLanguage;
+
+program
+    : statement+ EOF
+    ;
+
+statement
+    : returnStatement
+    | declStatement
+    | blockStatment
+    | expressionStatement
+    ;
+
+
+expressionStatement
+    : IDENTIFIER '=' expression ';'
+    ;
+
+blockStatement
+    : '{' statement+ '}'
+    ;
+
+declStatement
+    : 'int' IDENTIFIER '=' expression ';'
+    ;
+
+returnStatement
+    : 'return' expression ';'
+    ;
+
+expression
+    : additiveExpression
+    ;
+
+additiveExpression
+    : multiplicativeExpression (('+' | '-') multiplicativeExpression)*
+    ;
+
+multiplicativeExpression
+    : unaryExpression (('*' | '/') unaryExpression)*
+    ;
+
+unaryExpression
+    : ('-') unaryExpression
+    | primaryExpression
+    ;
+
+primaryExpression
+    : IDENTIFIER
+    | INTEGER_LITERAL
+    | '(' expression ')'
+    ;
+
+INTEGER_LITERAL
+    : [1-9][0-9]*
+    | [0]
+    ;
+
+IDENTIFIER
+    : NON_DIGIT (NON_DIGIT | DIGIT)*
+    ;
+
+NON_DIGIT: [a-zA-Z_];
+DEC_DIGIT: [0-9];
+```
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new file mode 100644
index 00000000..7008a44e
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+int a=1; int b=2; int c=0; { int b=3; c=a+b;  } return c;
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+	ordering="in";
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+	Add7 -> Con_3[taillabel=1];
+	Add7 -> Con_6[taillabel=2];
+	edge [style=dashed color=cornflowerblue];
+	Scope1_0:"Scope1_0_a" -> Con_3;
+	Scope1_0:"Scope1_0_b" -> Con_4;
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+	Scope1_1:"Scope1_1_b" -> Con_6;
+}
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+<svg aria-label="Compiler graph" width="888" height="208" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 888 208" style="font-family: sans-serif;"><style>
+    html, body { height:100%; margin:0; font-family:sans-serif; }
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+    #graph svg { display:block; }
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+Type not computed
+
+[0] → #3  ASSOC  0: a
+[1] → #4  ASSOC  0: b
+[2] → #7  ASSOC  0: c
+[3] → #6  ASSOC  1: b</title><line class="row" x1="0" x2="192" y1="30" y2="30"/><line class="row" x1="48" x2="48" y1="0" y2="30"/><line class="row" x1="96" x2="96" y1="0" y2="30"/><line class="row" x1="144" x2="144" y1="0" y2="30"/><text class="bind" x="24" y="20" text-anchor="middle">0: a</text><text class="bind" x="72" y="20" text-anchor="middle">0: b</text><text class="bind" x="120" y="20" text-anchor="middle">0: c</text><text class="bind" x="168" y="20" text-anchor="middle">1: b</text><circle class="port" cx="24" cy="0" r="3" fill="#536477"/><circle class="port" cx="72" cy="0" r="3" fill="#536477"/><circle class="port" cx="120" cy="0" r="3" fill="#536477"/><circle class="port" cx="168" cy="0" r="3" fill="#536477"/><text class="slot" x="24" y="-7" text-anchor="middle">0</text><text class="slot" x="72" y="-7" text-anchor="middle">1</text><text class="slot" x="120" y="-7" text-anchor="middle">2</text><text class="slot" x="168" y="-7" text-anchor="middle">3</text></g><g class="node" id="n2" data-id="2" transform="translate(24,30)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Start</tspan><tspan class="node-id">  #2</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#2 Start
+Type not computed
+
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+Type not computed
+
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+Type not computed
+
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+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n7" data-id="7" transform="translate(176,134)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>+</tspan><tspan class="node-id">  #7</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#7 +
+Type not computed
+
+[0] → —  DATA
+[1] → #3  DATA
+[2] → #6  DATA</title><circle class="port" cx="30" cy="-3" r="3" fill="white"/><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><circle class="port" cx="90" cy="-3" r="3" fill="#536477"/><text class="slot" x="30" y="-10" text-anchor="middle">0</text><text class="slot" x="60" y="-10" text-anchor="middle">1</text><text class="slot" x="90" y="-10" text-anchor="middle">2</text></g></g><g class="region-heads" style="opacity: 1;"/><g class="shortcuts" style="opacity: 1;"/><g class="peep-ghosts" pointer-events="none"/></g></svg>
diff --git a/docs/chapter03/03-graph2.gv b/docs/chapter03/03-graph2.gv
new file mode 100644
index 00000000..cafa7f25
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+int a=1; int b=2; int c=0; { int b=3; c=a+b;  } return c;
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+	Return8 -> Start2[taillabel=0 color=red];
+	Return8 -> Add7[taillabel=1];
+	edge [style=dashed color=cornflowerblue];
+	Scope1_0:"Scope1_0_a" -> Con_3;
+	Scope1_0:"Scope1_0_b" -> Con_4;
+	Scope1_0:"Scope1_0_c" -> Add7;
+}
diff --git a/docs/chapter03/03-graph2.json b/docs/chapter03/03-graph2.json
new file mode 100644
index 00000000..80397161
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+++ b/docs/chapter03/03-graph2.json
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+    {"id": 8, "label": "Return", "type": null, "kind": "CTRL", "edges": [{"idx": 0, "def": 2, "role": "CTRL", "label": null}, {"idx": 1, "def": 7, "role": "DATA", "label": null}], "proj": null}
+  ],
+  "groups": [
+  ]
+}
diff --git a/docs/chapter03/03-graph2.svg b/docs/chapter03/03-graph2.svg
new file mode 100644
index 00000000..3904d87e
--- /dev/null
+++ b/docs/chapter03/03-graph2.svg
@@ -0,0 +1,89 @@
+<svg aria-label="Compiler graph" width="840" height="312" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 840 312" style="font-family: sans-serif;"><style>
+    html, body { height:100%; margin:0; font-family:sans-serif; }
+    .viewer { height:100%; display:grid; grid-template-rows:auto minmax(0,1fr) auto; }
+    .source { padding:8px; border-bottom:1px solid #ccc; }
+    #program { width:min(600px,80vw); vertical-align:middle; }
+    #status { margin-top:4px; }
+    #graph { min-height:0; overflow:hidden; position:relative; background:#fafbfc; }
+    #elk { width:100%; height:100%; }
+    #graph svg { display:block; }
+    .tools { display:flex; flex-wrap:wrap; align-items:center; gap:14px; margin-top:8px; font-size:12px; }
+    .hint { color:#616c78; }
+    .ctrl { color:#b63838; } .mem { color:#2867b2; } .data { color:#536477; }
+    .edge { fill:none; stroke-width:1.5; }
+    .edge.CTRL { stroke-width:2; }
+    .edge.ASSOC { stroke-dasharray:4 4; }
+    .edge.PARSER { stroke-dasharray:5 4; }
+    .parser rect { fill:#f6f0ff; stroke:#7956a5; stroke-width:1.5; stroke-dasharray:5 4; }
+    .edge.selected { stroke-width:3.5; }
+    .edge.bundle { stroke-width:4; }
+    .edge.bundle.selected { stroke-width:6; }
+    .edge-hit { fill:none; stroke:transparent; stroke-width:12; vector-effect:non-scaling-stroke; pointer-events:stroke; cursor:pointer; }
+    .edge-jump { fill:transparent; pointer-events:all; cursor:pointer; }
+    .node { cursor:pointer; }
+    .box { stroke:#758191; stroke-width:1; }
+    .node.held .box { stroke-dasharray:5 3; }
+    .node.near .box { stroke:#c18221; stroke-width:2; }
+    .node.focus .box { stroke:#9c4900; stroke-width:3; }
+    .node.selected .box { stroke:#1569b9; stroke-width:3; }
+    .node.folded .box { stroke-width:4; }
+    .node.folding .box { fill:#f4ccd7; }
+    .fold-tag { font-size:9px; font-weight:700; fill:#963751; }
+    .peep-area { fill:#fff3d9; fill-opacity:.8; stroke:#c18221; stroke-width:2; pointer-events:none; }
+    .node.peep-edit .box { stroke:#9c4900; stroke-width:3; }
+    .node.error .box { stroke:#b42318; stroke-width:4; }
+    #event.error { color:#b42318; font-weight:600; white-space:pre-wrap; overflow-wrap:anywhere; }
+    .peep-ghosts { pointer-events:none; }
+    .region-box { stroke:#9da9b8; stroke-width:1.5; }
+    .fold-btn { cursor:pointer; }
+    .fold-btn rect { fill:white; stroke:#596674; }
+    .fold-btn text { font-size:14px; fill:#152330; }
+    .fold-btn:focus rect { stroke:#1569b9; stroke-width:2; }
+    .shortcut { cursor:pointer; }
+    .shortcut path { fill:none; stroke-width:1.5; }
+    .shortcut rect { fill:#fff8ec; stroke:#b63838; stroke-dasharray:3 2; }
+    .shortcut text { font-size:11px; fill:#783030; }
+    .shortcut.selected rect, .shortcut:focus rect { stroke-width:2.5; }
+    .label { font-size:12px; fill:#152330; font-weight:600; }
+    .node-id { font-size:10px; fill:#596674; font-weight:400; }
+    .type { font-size:11px; fill:#455768; }
+    .port { stroke:#536477; stroke-width:1; }
+    .row { stroke:#b6afcf; stroke-width:1; }
+    .bind { font-size:12px; fill:#152330; }
+    .slot { font-size:10px; fill:#364352; paint-order:stroke; stroke:#fafbfc; stroke-width:3; }
+    #detail { position:absolute; top:8px; right:8px; margin:0; padding:12px; max-width:320px;
+      max-height:45%; overflow:auto; white-space:pre-wrap; overflow-wrap:anywhere;
+      background:#fffffff2; border:1px solid #bac5d0; border-radius:4px; font-size:12px; }
+    .controls { display:flex; flex-wrap:wrap; justify-content:center; align-items:center; gap:6px; padding:6px; }
+    .button { color:white; background:black; font-size:20px; min-width:30px; }
+    .button:disabled { background:grey; }
+    .count { font-size:20px; min-width:35px; text-align:center; }
+    #N { width:6ch; }
+    #scrub { width:clamp(120px,35vw,600px); }
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+Type not computed
+
+[0] → #3  ASSOC  0: a
+[1] → #4  ASSOC  0: b
+[2] → #7  ASSOC  0: c</title><line class="row" x1="0" x2="144" y1="30" y2="30"/><line class="row" x1="48" x2="48" y1="0" y2="30"/><line class="row" x1="96" x2="96" y1="0" y2="30"/><text class="bind" x="24" y="20" text-anchor="middle">0: a</text><text class="bind" x="72" y="20" text-anchor="middle">0: b</text><text class="bind" x="120" y="20" text-anchor="middle">0: c</text><circle class="port" cx="24" cy="0" r="3" fill="#536477"/><circle class="port" cx="72" cy="0" r="3" fill="#536477"/><circle class="port" cx="120" cy="0" r="3" fill="#536477"/><text class="slot" x="24" y="-7" text-anchor="middle">0</text><text class="slot" x="72" y="-7" text-anchor="middle">1</text><text class="slot" x="120" y="-7" text-anchor="middle">2</text></g><g class="node" id="n2" data-id="2" transform="translate(24,134)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Start</tspan><tspan class="node-id">  #2</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#2 Start
+Type not computed
+
+</title></g><g class="node" id="n3" data-id="3" transform="translate(176,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#1</tspan><tspan class="node-id">  #3</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#3 #1
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n4" data-id="4" transform="translate(328,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#2</tspan><tspan class="node-id">  #4</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#4 #2
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n6" data-id="6" transform="translate(480,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#3</tspan><tspan class="node-id">  #6</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#6 #3
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n7" data-id="7" transform="translate(176,134)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>+</tspan><tspan class="node-id">  #7</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#7 +
+Type not computed
+
+[0] → —  DATA
+[1] → #3  DATA
+[2] → #6  DATA</title><circle class="port" cx="30" cy="-3" r="3" fill="white"/><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><circle class="port" cx="90" cy="-3" r="3" fill="#536477"/><text class="slot" x="30" y="-10" text-anchor="middle">0</text><text class="slot" x="60" y="-10" text-anchor="middle">1</text><text class="slot" x="90" y="-10" text-anchor="middle">2</text></g><g class="node" id="n8" data-id="8" transform="translate(44,238)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Return</tspan><tspan class="node-id">  #8</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#8 Return
+Type not computed
+
+[0] → #2  CTRL
+[1] → #7  DATA</title><circle class="port" cx="40" cy="-3" r="3" fill="#536477"/><circle class="port" cx="80" cy="-3" r="3" fill="#536477"/><text class="slot" x="40" y="-10" text-anchor="middle">0</text><text class="slot" x="80" y="-10" text-anchor="middle">1</text></g></g><g class="region-heads" style="opacity: 1;"/><g class="shortcuts" style="opacity: 1;"/><g class="peep-ghosts" pointer-events="none"/></g></svg>
diff --git a/docs/chapter03/03-graph3.gv b/docs/chapter03/03-graph3.gv
new file mode 100644
index 00000000..791a7dc1
--- /dev/null
+++ b/docs/chapter03/03-graph3.gv
@@ -0,0 +1,37 @@
+digraph chapter03 {
+/*
+int x0=1; int y0=2; int x1=3; int y1=4; return (x0-x1)*(x0-x1) + (y0-y1)*(y0-y1);
+*/
+	rankdir=BT;
+	ordering="in";
+	concentrate="true";
+	subgraph cluster_Nodes {
+		Start2 [ shape=box style=filled fillcolor=yellow label="Start" ];
+		Con_3 [ label="#1" ];
+		Con_4 [ label="#2" ];
+		Con_20 [ label="#8" ];
+		Con_5 [ label="#3" ];
+		Return21 [ shape=box style=filled fillcolor=yellow label="Return" ];
+		Con_6 [ label="#4" ];
+	}
+	node [shape=plaintext];
+	subgraph cluster_Scope1_0 {
+		Scope1_0 [label=<
+			<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
+			<TR><TD BGCOLOR="cyan">0</TD><TD PORT="Scope1_0_y0">y0</TD><TD PORT="Scope1_0_x0">x0</TD><TD PORT="Scope1_0_y1">y1</TD><TD PORT="Scope1_0_x1">x1</TD></TR>
+			</TABLE>>];
+	}
+	edge [ fontname=Helvetica, fontsize=8 ];
+	Con_3 -> Start2[taillabel=0 style=dotted];
+	Con_4 -> Start2[taillabel=0 style=dotted];
+	Con_20 -> Start2[taillabel=0 style=dotted];
+	Con_5 -> Start2[taillabel=0 style=dotted];
+	Return21 -> Start2[taillabel=0 color=red];
+	Return21 -> Con_20[taillabel=1];
+	Con_6 -> Start2[taillabel=0 style=dotted];
+	edge [style=dashed color=cornflowerblue];
+	Scope1_0:"Scope1_0_y0" -> Con_4;
+	Scope1_0:"Scope1_0_x0" -> Con_3;
+	Scope1_0:"Scope1_0_y1" -> Con_6;
+	Scope1_0:"Scope1_0_x1" -> Con_5;
+}
diff --git a/docs/chapter03/03-graph3.json b/docs/chapter03/03-graph3.json
new file mode 100644
index 00000000..a6d6175a
--- /dev/null
+++ b/docs/chapter03/03-graph3.json
@@ -0,0 +1,19 @@
+{
+  "ver": 1,
+  "comp": "chapter03/docs/03-graph3.svg",
+  "step": 1,
+  "roots": [],
+  "scope": 0,
+  "nodes": [
+    {"id": 1, "label": "Scope", "type": null, "kind": "SCOPE", "edges": [{"idx": 0, "def": 4, "role": "ASSOC", "label": "0: y0"}, {"idx": 1, "def": 3, "role": "ASSOC", "label": "0: x0"}, {"idx": 2, "def": 6, "role": "ASSOC", "label": "0: y1"}, {"idx": 3, "def": 5, "role": "ASSOC", "label": "0: x1"}], "proj": null},
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+  ],
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+}
diff --git a/docs/chapter03/03-graph3.svg b/docs/chapter03/03-graph3.svg
new file mode 100644
index 00000000..4c5db5e0
--- /dev/null
+++ b/docs/chapter03/03-graph3.svg
@@ -0,0 +1,91 @@
+<svg aria-label="Compiler graph" width="1204" height="208" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1204 208" style="font-family: sans-serif;"><style>
+    html, body { height:100%; margin:0; font-family:sans-serif; }
+    .viewer { height:100%; display:grid; grid-template-rows:auto minmax(0,1fr) auto; }
+    .source { padding:8px; border-bottom:1px solid #ccc; }
+    #program { width:min(600px,80vw); vertical-align:middle; }
+    #status { margin-top:4px; }
+    #graph { min-height:0; overflow:hidden; position:relative; background:#fafbfc; }
+    #elk { width:100%; height:100%; }
+    #graph svg { display:block; }
+    .tools { display:flex; flex-wrap:wrap; align-items:center; gap:14px; margin-top:8px; font-size:12px; }
+    .hint { color:#616c78; }
+    .ctrl { color:#b63838; } .mem { color:#2867b2; } .data { color:#536477; }
+    .edge { fill:none; stroke-width:1.5; }
+    .edge.CTRL { stroke-width:2; }
+    .edge.ASSOC { stroke-dasharray:4 4; }
+    .edge.PARSER { stroke-dasharray:5 4; }
+    .parser rect { fill:#f6f0ff; stroke:#7956a5; stroke-width:1.5; stroke-dasharray:5 4; }
+    .edge.selected { stroke-width:3.5; }
+    .edge.bundle { stroke-width:4; }
+    .edge.bundle.selected { stroke-width:6; }
+    .edge-hit { fill:none; stroke:transparent; stroke-width:12; vector-effect:non-scaling-stroke; pointer-events:stroke; cursor:pointer; }
+    .edge-jump { fill:transparent; pointer-events:all; cursor:pointer; }
+    .node { cursor:pointer; }
+    .box { stroke:#758191; stroke-width:1; }
+    .node.held .box { stroke-dasharray:5 3; }
+    .node.near .box { stroke:#c18221; stroke-width:2; }
+    .node.focus .box { stroke:#9c4900; stroke-width:3; }
+    .node.selected .box { stroke:#1569b9; stroke-width:3; }
+    .node.folded .box { stroke-width:4; }
+    .node.folding .box { fill:#f4ccd7; }
+    .fold-tag { font-size:9px; font-weight:700; fill:#963751; }
+    .peep-area { fill:#fff3d9; fill-opacity:.8; stroke:#c18221; stroke-width:2; pointer-events:none; }
+    .node.peep-edit .box { stroke:#9c4900; stroke-width:3; }
+    .node.error .box { stroke:#b42318; stroke-width:4; }
+    #event.error { color:#b42318; font-weight:600; white-space:pre-wrap; overflow-wrap:anywhere; }
+    .peep-ghosts { pointer-events:none; }
+    .region-box { stroke:#9da9b8; stroke-width:1.5; }
+    .fold-btn { cursor:pointer; }
+    .fold-btn rect { fill:white; stroke:#596674; }
+    .fold-btn text { font-size:14px; fill:#152330; }
+    .fold-btn:focus rect { stroke:#1569b9; stroke-width:2; }
+    .shortcut { cursor:pointer; }
+    .shortcut path { fill:none; stroke-width:1.5; }
+    .shortcut rect { fill:#fff8ec; stroke:#b63838; stroke-dasharray:3 2; }
+    .shortcut text { font-size:11px; fill:#783030; }
+    .shortcut.selected rect, .shortcut:focus rect { stroke-width:2.5; }
+    .label { font-size:12px; fill:#152330; font-weight:600; }
+    .node-id { font-size:10px; fill:#596674; font-weight:400; }
+    .type { font-size:11px; fill:#455768; }
+    .port { stroke:#536477; stroke-width:1; }
+    .row { stroke:#b6afcf; stroke-width:1; }
+    .bind { font-size:12px; fill:#152330; }
+    .slot { font-size:10px; fill:#364352; paint-order:stroke; stroke:#fafbfc; stroke-width:3; }
+    #detail { position:absolute; top:8px; right:8px; margin:0; padding:12px; max-width:320px;
+      max-height:45%; overflow:auto; white-space:pre-wrap; overflow-wrap:anywhere;
+      background:#fffffff2; border:1px solid #bac5d0; border-radius:4px; font-size:12px; }
+    .controls { display:flex; flex-wrap:wrap; justify-content:center; align-items:center; gap:6px; padding:6px; }
+    .button { color:white; background:black; font-size:20px; min-width:30px; }
+    .button:disabled { background:grey; }
+    .count { font-size:20px; min-width:35px; text-align:center; }
+    #N { width:6ch; }
+    #scrub { width:clamp(120px,35vw,600px); }
+  </style><defs><marker id="arrow-CTRL" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#b63838"/></marker><marker id="arrow-DATA" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#536477"/></marker><marker id="arrow-MEM" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#2867b2"/></marker><marker id="arrow-ASSOC" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#9396a3"/></marker><marker id="arrow-PARSER" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#7956a5"/></marker></defs><rect width="100%" height="100%" fill="rgb(250, 251, 252)"/><g><g class="regions" style="opacity: 1;"/><rect class="peep-area" rx="36" style="opacity: 0;"/><g class="edges"><path class="edge ASSOC" id="e1i0" d="M388,77 C388,101 1001.5,74 1001.5,98" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#1[0] → #4 · ASSOC · 0: y0</title></path><path class="edge ASSOC" id="e1i1" d="M236,77 C236,101 1052.5,74 1052.5,98" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#1[1] → #3 · ASSOC · 0: x0</title></path><path class="edge ASSOC" id="e1i2" d="M692,77 C692,101 1103.5,74 1103.5,98" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#1[2] → #6 · ASSOC · 0: y1</title></path><path class="edge ASSOC" id="e1i3" d="M540,77 C540,101 1154.5,74 1154.5,98" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#1[3] → #5 · ASSOC · 0: x1</title></path><path class="edge ASSOC" id="e3i0" d="M84,77 C84,101 236,3 236,27" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#3[0] → #2 · ASSOC</title></path><path class="edge ASSOC" id="e4i0" d="M84,77 C84,101 388,3 388,27" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#4[0] → #2 · ASSOC</title></path><path class="edge ASSOC" id="e5i0" d="M84,77 C84,101 540,3 540,27" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#5[0] → #2 · ASSOC</title></path><path class="edge ASSOC" id="e6i0" d="M84,77 C84,101 692,3 692,27" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#6[0] → #2 · ASSOC</title></path><path class="edge ASSOC" id="e20i0" d="M84,77 C84,101 844,3 844,27" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#20[0] → #2 · ASSOC</title></path><path class="edge CTRL" id="e21i0" d="M84,80 L84,128" stroke="#b63838" marker-start="url(#arrow-CTRL)" style="opacity: 1;"><title>#21[0] → #2 · CTRL</title></path><path class="edge DATA" id="e21i1" d="M844,80 L844,85 Q844,90 839,90 L132,90 Q124,90 124,98 L124,128" stroke="#536477" marker-start="url(#arrow-DATA)" style="opacity: 1;"><title>#21[1] → #20 · DATA</title></path></g><g class="edge-hits"/><g class="parser" style="opacity: 1;"/><g class="nodes"><g class="node" id="n1" data-id="1" transform="translate(976,98)" style="opacity: 1;"><path class="box" d="M4,0H200Q204,0 204,4V52Q204,56 200,56H4Q0,56 0,52V4Q0,0 4,0Z" fill="#e5e0ff"/><text class="label" text-anchor="middle" x="102" y="48"><tspan>Scope</tspan><tspan class="node-id">  #1</tspan></text><text class="type" text-anchor="middle" y="35" x="102"/><title>#1 Scope
+Type not computed
+
+[0] → #4  ASSOC  0: y0
+[1] → #3  ASSOC  0: x0
+[2] → #6  ASSOC  0: y1
+[3] → #5  ASSOC  0: x1</title><line class="row" x1="0" x2="204" y1="30" y2="30"/><line class="row" x1="51" x2="51" y1="0" y2="30"/><line class="row" x1="102" x2="102" y1="0" y2="30"/><line class="row" x1="153" x2="153" y1="0" y2="30"/><text class="bind" x="25.5" y="20" text-anchor="middle">0: y0</text><text class="bind" x="76.5" y="20" text-anchor="middle">0: x0</text><text class="bind" x="127.5" y="20" text-anchor="middle">0: y1</text><text class="bind" x="178.5" y="20" text-anchor="middle">0: x1</text><circle class="port" cx="25.5" cy="0" r="3" fill="#536477"/><circle class="port" cx="76.5" cy="0" r="3" fill="#536477"/><circle class="port" cx="127.5" cy="0" r="3" fill="#536477"/><circle class="port" cx="178.5" cy="0" r="3" fill="#536477"/><text class="slot" x="25.5" y="-7" text-anchor="middle">0</text><text class="slot" x="76.5" y="-7" text-anchor="middle">1</text><text class="slot" x="127.5" y="-7" text-anchor="middle">2</text><text class="slot" x="178.5" y="-7" text-anchor="middle">3</text></g><g class="node" id="n2" data-id="2" transform="translate(24,30)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Start</tspan><tspan class="node-id">  #2</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#2 Start
+Type not computed
+
+</title></g><g class="node" id="n3" data-id="3" transform="translate(176,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#1</tspan><tspan class="node-id">  #3</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#3 #1
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n4" data-id="4" transform="translate(328,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#2</tspan><tspan class="node-id">  #4</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#4 #2
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n5" data-id="5" transform="translate(480,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#3</tspan><tspan class="node-id">  #5</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#5 #3
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n6" data-id="6" transform="translate(632,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#4</tspan><tspan class="node-id">  #6</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#6 #4
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n20" data-id="20" transform="translate(784,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#8</tspan><tspan class="node-id">  #20</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#20 #8
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n21" data-id="21" transform="translate(44,134)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Return</tspan><tspan class="node-id">  #21</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#21 Return
+Type not computed
+
+[0] → #2  CTRL
+[1] → #20  DATA</title><circle class="port" cx="40" cy="-3" r="3" fill="#536477"/><circle class="port" cx="80" cy="-3" r="3" fill="#536477"/><text class="slot" x="40" y="-10" text-anchor="middle">0</text><text class="slot" x="80" y="-10" text-anchor="middle">1</text></g></g><g class="region-heads" style="opacity: 1;"/><g class="shortcuts" style="opacity: 1;"/><g class="peep-ghosts" pointer-events="none"/></g></svg>
diff --git a/docs/chapter03/03-graph4.json b/docs/chapter03/03-graph4.json
new file mode 100644
index 00000000..b594eee2
--- /dev/null
+++ b/docs/chapter03/03-graph4.json
@@ -0,0 +1,17 @@
+{
+  "ver": 1,
+  "comp": "chapter03/docs/03-graph4.svg",
+  "step": 1,
+  "roots": [],
+  "scope": 0,
+  "nodes": [
+    {"id": 1, "label": "Scope", "type": null, "kind": "SCOPE", "edges": [{"idx": 0, "def": 3, "role": "ASSOC", "label": "0: a"}, {"idx": 1, "def": 4, "role": "ASSOC", "label": "0: b"}, {"idx": 2, "def": 8, "role": "ASSOC", "label": "0: c"}, {"idx": 3, "def": 6, "role": "ASSOC", "label": "1: b"}], "proj": null},
+    {"id": 2, "label": "Start", "type": null, "kind": "CTRL", "edges": [], "proj": null},
+    {"id": 3, "label": "#1", "type": null, "kind": "DATA", "edges": [{"idx": 0, "def": 2, "role": "ASSOC", "label": null}], "proj": null},
+    {"id": 4, "label": "#2", "type": null, "kind": "DATA", "edges": [{"idx": 0, "def": 2, "role": "ASSOC", "label": null}], "proj": null},
+    {"id": 6, "label": "#5", "type": null, "kind": "DATA", "edges": [{"idx": 0, "def": 2, "role": "ASSOC", "label": null}], "proj": null},
+    {"id": 8, "label": "#6", "type": null, "kind": "DATA", "edges": [{"idx": 0, "def": 2, "role": "ASSOC", "label": null}], "proj": null}
+  ],
+  "groups": [
+  ]
+}
diff --git a/docs/chapter03/03-graph4.svg b/docs/chapter03/03-graph4.svg
new file mode 100644
index 00000000..c773ef9b
--- /dev/null
+++ b/docs/chapter03/03-graph4.svg
@@ -0,0 +1,84 @@
+<svg aria-label="Compiler graph" width="1040" height="178" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1040 178" style="font-family: sans-serif;"><style>
+    html, body { height:100%; margin:0; font-family:sans-serif; }
+    .viewer { height:100%; display:grid; grid-template-rows:auto minmax(0,1fr) auto; }
+    .source { padding:8px; border-bottom:1px solid #ccc; }
+    #program { width:min(600px,80vw); vertical-align:middle; }
+    #status { margin-top:4px; }
+    #graph { min-height:0; overflow:hidden; position:relative; background:#fafbfc; }
+    #elk { width:100%; height:100%; }
+    #graph svg { display:block; }
+    .tools { display:flex; flex-wrap:wrap; align-items:center; gap:14px; margin-top:8px; font-size:12px; }
+    .hint { color:#616c78; }
+    .ctrl { color:#b63838; } .mem { color:#2867b2; } .data { color:#536477; }
+    .edge { fill:none; stroke-width:1.5; }
+    .edge.CTRL { stroke-width:2; }
+    .edge.ASSOC { stroke-dasharray:4 4; }
+    .edge.PARSER { stroke-dasharray:5 4; }
+    .parser rect { fill:#f6f0ff; stroke:#7956a5; stroke-width:1.5; stroke-dasharray:5 4; }
+    .edge.selected { stroke-width:3.5; }
+    .edge.bundle { stroke-width:4; }
+    .edge.bundle.selected { stroke-width:6; }
+    .edge-hit { fill:none; stroke:transparent; stroke-width:12; vector-effect:non-scaling-stroke; pointer-events:stroke; cursor:pointer; }
+    .edge-jump { fill:transparent; pointer-events:all; cursor:pointer; }
+    .node { cursor:pointer; }
+    .box { stroke:#758191; stroke-width:1; }
+    .node.held .box { stroke-dasharray:5 3; }
+    .node.near .box { stroke:#c18221; stroke-width:2; }
+    .node.focus .box { stroke:#9c4900; stroke-width:3; }
+    .node.selected .box { stroke:#1569b9; stroke-width:3; }
+    .node.folded .box { stroke-width:4; }
+    .node.folding .box { fill:#f4ccd7; }
+    .fold-tag { font-size:9px; font-weight:700; fill:#963751; }
+    .peep-area { fill:#fff3d9; fill-opacity:.8; stroke:#c18221; stroke-width:2; pointer-events:none; }
+    .node.peep-edit .box { stroke:#9c4900; stroke-width:3; }
+    .node.error .box { stroke:#b42318; stroke-width:4; }
+    #event.error { color:#b42318; font-weight:600; white-space:pre-wrap; overflow-wrap:anywhere; }
+    .peep-ghosts { pointer-events:none; }
+    .region-box { stroke:#9da9b8; stroke-width:1.5; }
+    .fold-btn { cursor:pointer; }
+    .fold-btn rect { fill:white; stroke:#596674; }
+    .fold-btn text { font-size:14px; fill:#152330; }
+    .fold-btn:focus rect { stroke:#1569b9; stroke-width:2; }
+    .shortcut { cursor:pointer; }
+    .shortcut path { fill:none; stroke-width:1.5; }
+    .shortcut rect { fill:#fff8ec; stroke:#b63838; stroke-dasharray:3 2; }
+    .shortcut text { font-size:11px; fill:#783030; }
+    .shortcut.selected rect, .shortcut:focus rect { stroke-width:2.5; }
+    .label { font-size:12px; fill:#152330; font-weight:600; }
+    .node-id { font-size:10px; fill:#596674; font-weight:400; }
+    .type { font-size:11px; fill:#455768; }
+    .port { stroke:#536477; stroke-width:1; }
+    .row { stroke:#b6afcf; stroke-width:1; }
+    .bind { font-size:12px; fill:#152330; }
+    .slot { font-size:10px; fill:#364352; paint-order:stroke; stroke:#fafbfc; stroke-width:3; }
+    #detail { position:absolute; top:8px; right:8px; margin:0; padding:12px; max-width:320px;
+      max-height:45%; overflow:auto; white-space:pre-wrap; overflow-wrap:anywhere;
+      background:#fffffff2; border:1px solid #bac5d0; border-radius:4px; font-size:12px; }
+    .controls { display:flex; flex-wrap:wrap; justify-content:center; align-items:center; gap:6px; padding:6px; }
+    .button { color:white; background:black; font-size:20px; min-width:30px; }
+    .button:disabled { background:grey; }
+    .count { font-size:20px; min-width:35px; text-align:center; }
+    #N { width:6ch; }
+    #scrub { width:clamp(120px,35vw,600px); }
+  </style><defs><marker id="arrow-CTRL" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#b63838"/></marker><marker id="arrow-DATA" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#536477"/></marker><marker id="arrow-MEM" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#2867b2"/></marker><marker id="arrow-ASSOC" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#9396a3"/></marker><marker id="arrow-PARSER" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#7956a5"/></marker></defs><rect width="100%" height="100%" fill="rgb(250, 251, 252)"/><g><g class="regions" style="opacity: 1;"/><rect class="peep-area" rx="36" style="opacity: 0;"/><g class="edges"><path class="edge ASSOC" id="e1i0" d="M236,77 C236,101 848,74 848,98" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#1[0] → #3 · ASSOC · 0: a</title></path><path class="edge ASSOC" id="e1i1" d="M388,77 C388,101 896,74 896,98" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#1[1] → #4 · ASSOC · 0: b</title></path><path class="edge ASSOC" id="e1i2" d="M692,77 C692,101 944,74 944,98" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#1[2] → #8 · ASSOC · 0: c</title></path><path class="edge ASSOC" id="e1i3" d="M540,77 C540,101 992,74 992,98" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#1[3] → #6 · ASSOC · 1: b</title></path><path class="edge ASSOC" id="e3i0" d="M84,77 C84,101 236,3 236,27" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#3[0] → #2 · ASSOC</title></path><path class="edge ASSOC" id="e4i0" d="M84,77 C84,101 388,3 388,27" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#4[0] → #2 · ASSOC</title></path><path class="edge ASSOC" id="e6i0" d="M84,77 C84,101 540,3 540,27" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#6[0] → #2 · ASSOC</title></path><path class="edge ASSOC" id="e8i0" d="M84,77 C84,101 692,3 692,27" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#8[0] → #2 · ASSOC</title></path></g><g class="edge-hits"/><g class="parser" style="opacity: 1;"/><g class="nodes"><g class="node" id="n1" data-id="1" transform="translate(824,98)" style="opacity: 1;"><path class="box" d="M4,0H188Q192,0 192,4V52Q192,56 188,56H4Q0,56 0,52V4Q0,0 4,0Z" fill="#e5e0ff"/><text class="label" text-anchor="middle" x="96" y="48"><tspan>Scope</tspan><tspan class="node-id">  #1</tspan></text><text class="type" text-anchor="middle" y="35" x="96"/><title>#1 Scope
+Type not computed
+
+[0] → #3  ASSOC  0: a
+[1] → #4  ASSOC  0: b
+[2] → #8  ASSOC  0: c
+[3] → #6  ASSOC  1: b</title><line class="row" x1="0" x2="192" y1="30" y2="30"/><line class="row" x1="48" x2="48" y1="0" y2="30"/><line class="row" x1="96" x2="96" y1="0" y2="30"/><line class="row" x1="144" x2="144" y1="0" y2="30"/><text class="bind" x="24" y="20" text-anchor="middle">0: a</text><text class="bind" x="72" y="20" text-anchor="middle">0: b</text><text class="bind" x="120" y="20" text-anchor="middle">0: c</text><text class="bind" x="168" y="20" text-anchor="middle">1: b</text><circle class="port" cx="24" cy="0" r="3" fill="#536477"/><circle class="port" cx="72" cy="0" r="3" fill="#536477"/><circle class="port" cx="120" cy="0" r="3" fill="#536477"/><circle class="port" cx="168" cy="0" r="3" fill="#536477"/><text class="slot" x="24" y="-7" text-anchor="middle">0</text><text class="slot" x="72" y="-7" text-anchor="middle">1</text><text class="slot" x="120" y="-7" text-anchor="middle">2</text><text class="slot" x="168" y="-7" text-anchor="middle">3</text></g><g class="node" id="n2" data-id="2" transform="translate(24,30)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Start</tspan><tspan class="node-id">  #2</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#2 Start
+Type not computed
+
+</title></g><g class="node" id="n3" data-id="3" transform="translate(176,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#1</tspan><tspan class="node-id">  #3</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#3 #1
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n4" data-id="4" transform="translate(328,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#2</tspan><tspan class="node-id">  #4</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#4 #2
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n6" data-id="6" transform="translate(480,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#5</tspan><tspan class="node-id">  #6</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#6 #5
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n8" data-id="8" transform="translate(632,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#6</tspan><tspan class="node-id">  #8</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#8 #6
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g></g><g class="region-heads" style="opacity: 1;"/><g class="shortcuts" style="opacity: 1;"/><g class="peep-ghosts" pointer-events="none"/></g></svg>
diff --git a/docs/chapter03/03-graph5.json b/docs/chapter03/03-graph5.json
new file mode 100644
index 00000000..476ad586
--- /dev/null
+++ b/docs/chapter03/03-graph5.json
@@ -0,0 +1,17 @@
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diff --git a/docs/chapter03/03-graph5.svg b/docs/chapter03/03-graph5.svg
new file mode 100644
index 00000000..a62d03bb
--- /dev/null
+++ b/docs/chapter03/03-graph5.svg
@@ -0,0 +1,84 @@
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+Type not computed
+
+[0] → #3  ASSOC  0: a
+[1] → #4  ASSOC  0: b
+[2] → #11  ASSOC  0: c
+[3] → #9  ASSOC  1: e</title><line class="row" x1="0" x2="192" y1="30" y2="30"/><line class="row" x1="48" x2="48" y1="0" y2="30"/><line class="row" x1="96" x2="96" y1="0" y2="30"/><line class="row" x1="144" x2="144" y1="0" y2="30"/><text class="bind" x="24" y="20" text-anchor="middle">0: a</text><text class="bind" x="72" y="20" text-anchor="middle">0: b</text><text class="bind" x="120" y="20" text-anchor="middle">0: c</text><text class="bind" x="168" y="20" text-anchor="middle">1: e</text><circle class="port" cx="24" cy="0" r="3" fill="#536477"/><circle class="port" cx="72" cy="0" r="3" fill="#536477"/><circle class="port" cx="120" cy="0" r="3" fill="#536477"/><circle class="port" cx="168" cy="0" r="3" fill="#536477"/><text class="slot" x="24" y="-7" text-anchor="middle">0</text><text class="slot" x="72" y="-7" text-anchor="middle">1</text><text class="slot" x="120" y="-7" text-anchor="middle">2</text><text class="slot" x="168" y="-7" text-anchor="middle">3</text></g><g class="node" id="n2" data-id="2" transform="translate(24,30)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Start</tspan><tspan class="node-id">  #2</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#2 Start
+Type not computed
+
+</title></g><g class="node" id="n3" data-id="3" transform="translate(176,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#1</tspan><tspan class="node-id">  #3</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#3 #1
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n4" data-id="4" transform="translate(328,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#2</tspan><tspan class="node-id">  #4</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#4 #2
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n9" data-id="9" transform="translate(480,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#6</tspan><tspan class="node-id">  #9</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#9 #6
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n11" data-id="11" transform="translate(632,30)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#7</tspan><tspan class="node-id">  #11</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#11 #7
+Type not computed
+
+[0] → #2  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g></g><g class="region-heads" style="opacity: 1;"/><g class="shortcuts" style="opacity: 1;"/><g class="peep-ghosts" pointer-events="none"/></g></svg>
diff --git a/docs/chapter03/Makefile b/docs/chapter03/Makefile
new file mode 100644
index 00000000..6fa0f057
--- /dev/null
+++ b/docs/chapter03/Makefile
@@ -0,0 +1 @@
+include ../../graph/docs.mk
diff --git a/docs/chapter03/README.md b/docs/chapter03/README.md
new file mode 100644
index 00000000..29ff8ee4
--- /dev/null
+++ b/docs/chapter03/README.md
@@ -0,0 +1,191 @@
+# Chapter 3: Variable Declarations
+
+[Previous: Chapter 2](../chapter02/README.md) |
+[Next: Chapter 4](../chapter04/README.md)
+
+# Table of Contents
+
+1. [Extensions to Intermediate Representation](#extensions-to-intermediate-representation)
+2. [Symbol Tables](#symbol-tables)
+3. [ScopeNode](#scopenode)
+4. [Demonstration](#demonstration)
+5. [Enabling peephole optimizations](#enabling-peephole-optimizations)
+
+You can also read [this chapter](https://github.com/SeaOfNodes/Simple/tree/linear-chapter03) in a linear Git revision history on the [linear](https://github.com/SeaOfNodes/Simple/tree/linear) branch and [compare](https://github.com/SeaOfNodes/Simple/compare/linear-chapter02...linear-chapter03) it to the previous chapter.
+
+In this chapter we extend the language grammar to allow variable declarations. This allows us to write:
+
+```
+int a=1;
+int b=2;
+int c=0;
+{
+    int b=3;
+    c=a+b;
+}
+return c;
+```
+
+Here is the [complete language grammar](03-grammar.md) for this chapter.
+
+
+## Extensions to Intermediate Representation
+
+In this chapter we introduce:
+
+| Node Name | Type         | Description                    | Inputs                          | Value |
+|-----------|--------------|--------------------------------|---------------------------------|-------|
+| Scope     | Symbol Table | Represents scopes in the graph | All nodes that define variables | None  |
+
+and keep all nodes from prior chapters.
+
+## Symbol Tables
+
+To support variable declarations and lexical scopes, we introduce symbol tables
+in the parser. A symbol table maps names to nodes.
+
+We maintain a *stack* of symbol tables.
+When a new lexical scope is created we push a new symbol table to the stack;
+when scope exits the topmost symbol table is popped from the stack.
+
+Declaring a name adds it to the current symbol table.  If a name is assigned
+to, then its mapping in the most recent symbol table is updated.  If a name is
+accessed, its mapping is looked up in the symbol tables.  The lookup goes up
+the stack of symbol tables, in lexical order.
+
+## ScopeNode
+
+A ScopeNode encapsulates the stack of symbol tables that are used to implement lexical scopes.
+
+* The nodes referenced by the names in a lexical scope become inputs to the
+  ScopeNode; this makes ScopeNode a user of these values, thus keeping them
+  alive while a particular lexical scope is alive.  When the lexical scope
+  ends, those inputs are removed. This is crucial because peepholes will remove
+  dead Nodes and every new Node is effectively dead at the instant of creation.
+* In [Chapter 5](../chapter05/README.md) when we implement branches, the ScopeNode gets duplicated at a branch point and then gets merged when the branch joins. This allows
+  the names to evolve in each branch independently. At the merge point, names that have diverged require a Phi node.
+* In [Chapter 7](../chapter07/README.md) additional logic is deployed for handling Phis from back edges.
+* The ScopeNode is used to track some other values such as the Control token starting from [Chapter 4](../chapter04/README.md), and whole memory starting from [Chapter 10](../chapter10/README.md). Special name bindings are used
+  for these, and each name is tracked across branches and then merged at merge points.
+* In [Chapter 10](../chapter10/README.md) the ScopeNode is enhanced to also maintain the declared type for each name.
+
+From an implementation standpoint, each symbol table is represented as a `HashMap<String,Integer>`, where the `String` is the variable name, and the `Integer` is an index into the inputs of the
+ScopeNode. To access the Node associated with a name, first the symbol table is consulted, and then the ScopeNode's inputs to find the required Node.
+The stack of symbol tables is represented as `Stack<HashMap<String,Integer>>`.
+
+When a lexical scope is exited, we not only pop the symbol table representing the
+scope from the stack, but also remove the relevant input nodes.  If the variable's expression
+only exists for the Scope mapping (e.g., "just in case" the Parser parses code
+that uses the variable) this is when the expression dies:
+```
+  int a=1;
+  {
+      int b=a*a*a;
+  }  // When this scope closes and ends, b (and the cube of a) dies
+  return a;
+```
+
+
+In the visualization, we show the ScopeNode in a separate purple box. Each
+binding is labelled with its lexical scope level. We show the edge from each
+variable in the symbol table to the defining
+Node in the graph.
+
+The ScopeNode is neither a Data Node nor a Control Node; it really is a utility for maintaining symbol tables, name lookups, plays a crucial role in deciding where Phi nodes are required.
+Representing it as a Node allows us to leverage the Sea of Nodes def-use architecture to maintain liveness of values in scope.
+
+A ScopeNode has no outputs.
+
+## Demonstration
+
+We show the output from the following code.
+
+```
+01      int a=1;
+02      int b=2;
+03      int c=0;
+04      {
+05          int b=3;
+07          c=a+b;
+08      }
+09      return c;
+```
+
+* When we start parsing the example above, we start with a symbol table (at level 0).
+The variables `a`, `b`, and `c` are registered in this table.
+* On line 4, we start a nested scope. At this point, a new symbol table is pushed (at level 1).
+* On line 5, a variable `b` is declared. `b` is registered in the symbol table at level 1. This then
+hides the variable with the same name on line 2.
+* On line 7, we update the variable `c`. Variable lookup will find it in the symbol table at level 0.
+The schematic below shows the variable bindings and arithmetic before constant
+folding. The compiler applies peepholes as it builds the graph, so the actual
+result of this example is `return 4;`.
+
+![Graph1](./03-graph1.svg)
+
+The diagram shows the ScopeNode's bindings with their scope levels. The two
+bindings for `b` belong to different lexical scopes.
+
+* When we exit the nested scope on line 8, the symbol table at level 1 is popped.
+* At line 9, our graph looks like this:
+
+![Graph2](./03-graph2.svg)
+
+As we see, only 1 symbol table is present at this point.
+
+We can also have multiple scopes at the same level during the execution of the program,
+but only one will be active at a time because the symbol table can only hold one symbol table
+for each scope level.
+
+For example:
+```
+01   int a=1;
+02   int b=2;
+03   int c=0;
+04   {
+05       int b=5;
+06       c=a+b;
+08   }
+09   {
+10       int e=6;
+11       c = a+e;
+13   }
+14    return c;
+```
+Here both scopes starting from `(04-08)` and `(09-13)` are at the same level:
+```java
+public final Stack<HashMap<String, Integer>> _scopes;
+```
+The `_scopes` stack holds nested scopes, with index 0 representing the highest (global)
+scope and deeper indices representing more nested scopes.
+Popping returns the current scope and moves to the outer one.
+There is a direct one-to-one mapping between each index and its corresponding scope.
+
+The first nested scope (04-08):
+
+![Graph4](./03-graph4.svg)
+
+The second nested scope (09-13):
+
+![Graph5](./03-graph5.svg)
+
+ - In both cases the index which represents the depth of the scope is 1.
+## Enabling peephole optimizations
+
+Once we enable peephole optimizations, the parser is able to reduce all the expressions down to a
+constant. This is illustrated nicely below.
+
+```
+01      int x0=1;
+02      int y0=2;
+03      int x1=3;
+04      int y1=4;
+05      return (x0-x1)*(x0-x1) + (y0-y1)*(y0-y1);
+```
+
+The graph for the example above is displayed below.
+
+![Graph2](./03-graph3.svg)
+
+The return node has the constant `8` as its data value!  When the parsing ends
+and the scope at level 0 is removed, only the `return 8` remains.
author	Cliff Click <cliffc@acm.org>	2023-10-01 18:01:54 +0100
committer	Cliff Click <cliffc@acm.org>	2026-10-04 13:30:41 -0700
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