From 5a90102b20d18966b69496d85361d14c085479db Mon Sep 17 00:00:00 2001
From: Flavian Kaufmann <flavian@flaviankaufmann.ch>
Date: Wed, 21 May 2025 07:45:30 +0200
Subject: syntax doc

---
 README.md       | 44 +++++++++++++++++++++++++++++++++++++++++++-
 res/syntax.ebnf | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 src/driver.c    |  2 +-
 src/repl.c      | 14 +++++++-------
 4 files changed, 98 insertions(+), 9 deletions(-)
 create mode 100644 res/syntax.ebnf

diff --git a/README.md b/README.md
index dc39ac2..a86f2df 100644
--- a/README.md
+++ b/README.md
@@ -13,4 +13,46 @@ A small interpreter of the IMP programming language.
 
 - [flex](https://github.com/westes/flex)
 - [bison](https://www.gnu.org/software/bison)
-- [readline](https://tiswww.case.edu/php/chet/readline/rltop.html)
\ No newline at end of file
+- [readline](https://tiswww.case.edu/php/chet/readline/rltop.html)
+
+## IMP
+
+[Syntax](/res/syntax.ebnf)
+
+**Statement <stm>**
+Variable assignment:
+- `<var> := <aexp>` any variable not assigned, has the value 0.
+
+Local variable:
+- `var <var> := <aexp> in <stm> end`
+
+Control flow:
+- `if <bexp> then <stm> else <stm> end`
+- `while <bexp> do <stm> end`
+- `(<stm>; <stm>)` sequential composition, the first statement runs before the second
+- `skip`, nop
+
+**Expression**
+Arithmetic Expression <aexp>:
+- `<num>`
+- `<var>`
+- `(<aexp> + <aexp>)
+- `(<aexp> - <aexp>)
+- `(<aexp> + <aexp>)
+
+Boolean Expression <bexp>:
+- `not <bexp>
+- `(<bexp> or <bexp>)
+- `(<bexp> and <bexp>)
+- `<aexp> = <aexp>`
+- `<aexp> # <aexp>` not equals
+- `<aexp> < <aexp>`
+- `<aexp> <= <aexp>`
+- `<aexp> > <aexp>`
+- `<aexp> >= <aexp>`
+
+**Variable <var>**
+- `[a-zA-Z][A-Za-z0-9]*`
+
+**Numeral <num>**
+- `[0-9]+`
diff --git a/res/syntax.ebnf b/res/syntax.ebnf
new file mode 100644
index 0000000..85990c5
--- /dev/null
+++ b/res/syntax.ebnf
@@ -0,0 +1,47 @@
+letter_uppercase      = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M"
+                      | "N" | "O" | "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"
+                      ;
+
+letter_lowercase      = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m"
+                      | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z"
+                      ;
+
+letter                = letter_uppercase | letter_lowercase
+                      ;
+
+digit                 = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
+                      ;
+
+identifier            = letter , { letter | digit }
+                      ;
+
+numeral               = digit | ( numeral , digit )
+                      ;
+
+variable              = identifier
+                      ;
+
+arithmetic_operation  = "+" | "-" | "*"
+                      ;
+
+arithmetic_expression = ( "(" , arithmetic_expression , arithmetic_operation , arithmetic_expression , ")" )
+                      | variable | numeral ;
+
+boolean_operation     = "or" | "not"
+                      ;
+
+relational_operation  = "=" | "#" | "<" | "<=" | ">" | ">="
+                      ;
+
+boolean_expression    = ( "(" , boolean_expression , boolean_operation , boolean_expression , ")" )
+                      | ( "not" , boolean_expression )
+                      | ( arithmetic_expression , relational_operation , arithmetic_expression )
+                      ;
+
+statement             = "skip"
+                      | ( variable , ":=" , arithmetic_expression )
+                      | ( "(" , statement , ";" , "statement" , ")" )
+                      | ( "if" , boolean_expression , "then" , statement , "else" , statement , "end" )
+                      | ( "while" , boolean_expression , "do" , statement , "end" )
+                      | ( "var" , variable , ":=", arithmetic_expression , "in" , statement , "end" )
+                      ;
\ No newline at end of file
diff --git a/src/driver.c b/src/driver.c
index 60d3ce2..fc2a3ae 100644
--- a/src/driver.c
+++ b/src/driver.c
@@ -25,7 +25,7 @@ int main(int argc, char **argv) {
       fprintf(stderr, 
         "Usage: %s [-i program.imp]\n"
         "  -i <program.imp>   interpret program and exit\n"
-        "  (no args)   start REPL\n",
+        "  (no args)          start REPL\n",
         argv[0]);
       return (opt == 'h') ? EXIT_SUCCESS : EXIT_FAILURE;
     }
diff --git a/src/repl.c b/src/repl.c
index 9c61b98..5ea9792 100644
--- a/src/repl.c
+++ b/src/repl.c
@@ -7,14 +7,14 @@
 #include <string.h>
 
 static void print_help(void) {
-  puts(
-    "IMP REPL (type IMP statements or commands starting with '%')\n"
+  printf(
+    "IMP REPL (type IMP statements or commands starting with '%%')\n"
     "Commands:\n"
-    "  %quit                   exit\n"
-    "  %run <path/to/file.imp> interpret program\n"
-    "  %set <var> <val>        set variable\n"
-    "  %print [<var>]          print variable, or all variables\n"
-    "  %help                   show this message\n");
+    "  %%quit                   exit\n"
+    "  %%run <path/to/file.imp> interpret program\n"
+    "  %%set <var> <val>        set variable\n"
+    "  %%print [<var>]          print variable, or all variables\n"
+    "  %%help                   show this message\n");
 }
 
 static void repl_exec_command(hashmap_t context, const char *command) {
-- 
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