Improve multiline let formatting.

2 files changed, 43 insertions, 20 deletions

diff --git a/main.tex b/main.tex
index c2eaafe..0e0c6ff 100644
--- a/main.tex
+++ b/main.tex
@@ -171,21 +171,47 @@
 \newcommand\letkw{\ensuremath{\mathsf{let}}}
 \newcommand\lettm[3]{\letkw~{#2} \coloneq {#1}~\mathsf{in}~{#3}}
 \ExplSyntaxOn
-\NewDocumentCommand \squid_letpart {m m}
-  { \letkw & {#1} = \cr
-    & {#2} \cr
-    \mathsf{in} &
+%% args:
+%%   1. Do I need a & on the first line?
+%%   2. Binder name
+%%   3. Is value multiline?
+%%   4. Value
+\NewDocumentCommand \squid_letpart {m m m m}
+  { \IfBooleanTF{#3}
+      { \letkw \IfBooleanTF{#1}{&}{\nobreakspace} {#2} = \cr
+        & {#4} \cr
+        \mathsf{in}
+      }
+      { \letkw \IfBooleanTF{#1}{&}{\nobreakspace} {#2} = {#4} \nobreakspace \mathsf{in}
+      }
   }
-\NewDocumentCommand \squid_contlet {> {\SplitArgument{1}{=}} m}
-  { \squid_letpart #1 \squid_checklet [\cr]
+%% args:
+%%   1. Do I need a & on the first line?
+%%   2. Binder name
+%%   3. Is value multiline?
+%%   4. Value
+%%   ... further processing
+\NewDocumentCommand \squid_contlet {m m s m}
+  { \squid_letpart {#1} {#2} {#3} {#4}
+    \IfBooleanTF{#3}
+      { \squid_checklet [\BooleanFalse] }
+      { \squid_checklet [\BooleanTrue] }
   }
+%% args:
+%%   1. If something, do I need a new line?
+%%   2. Is the next arg not a binder?
+%%   ... further processing
 \NewDocumentCommand \squid_checklet {o s m}
   { \IfBooleanTF{#2}
-      { \IfNoValueF{#1}{#1} & {#3}
+      { \IfNoValueF{#1}{\IfBooleanT{#1}{\cr}} & {#3}
         \end{array}
         \wlog{End~let}
       }
-      { \IfNoValueF{#1}{#1} \squid_contlet {#3}
+      { \IfNoValueTF{#1}
+          { \squid_contlet \BooleanTrue {#3} }
+          { \IfBooleanTF{#1}{\cr}{&}
+            \squid_contlet {#1} {#3}
+          }
       }
   }
 \NewDocumentCommand \dolet {O{t}}
diff --git a/sec/systemt.ltx b/sec/systemt.ltx
index 54ba5f2..e66f499 100644
--- a/sec/systemt.ltx
+++ b/sec/systemt.ltx
@@ -171,8 +171,8 @@ the fold. Below is the fold over binary trees.
     \mathsf{leaf}(n). f(n);
     \mathsf{branch}(x, y). g(x, y)
   } \coloneq
-  \dolet{
-    go = \doprimrec*{t}{\arb}{h}{
+  \dolet{go}*{
+    \doprimrec*{t}{\arb}{h}{
       \lambda i. \domatch*{i}{
         \mathsf{leaf}(n). f(n);
         \mathsf{branch}(l, r). g(h(l), h(r))}}
@@ -206,21 +206,18 @@ respectively, and then case split on this sum. We detail this in \cref{fig:churc
       \mathsf{leaf}(n).     f(n);
       \mathsf{branch}(x,y). g(x, y)
     } \coloneq
-    \dolet[t]{
-      \roll = \lambda x. \domatch*[t]{x}{
+    \dolet[t]{\roll}*{
+      \lambda x. \domatch*[t]{x}{
         \mathsf{Left}(n).     \mathsf{leaf}(n);
-        \mathsf{Right}(x, y). \mathsf{branch}(x, y)
-      }
-    }{
-      x = \dofoldmatch*{t}{
+        \mathsf{Right}(x, y). \mathsf{branch}(x, y)}
+    }{x}*{
+      \dofoldmatch*{t}{
         \mathsf{leaf}(n).      \mathsf{Left}(n);
-        \mathsf{branch}(x, y). \mathsf{Right}(\roll~x, \roll~y)
-      }
+        \mathsf{branch}(x, y). \mathsf{Right}(\roll~x, \roll~y)}
     }*{
       \domatch*{x}{
         \mathsf{Left}(n).     f(n);
-        \mathsf{Right}(x, y). g(x, y)
-      }
+        \mathsf{Right}(x, y). g(x, y)}
     }
   \]
   \caption{How to perform pattern matching on binary trees for Church encodings.