Add variables

Signed-off-by: Christian Lindig <lindig@gmail.com>

lib/lexer.mll

@@ -8,6 +8,8 @@
 
 let digit  = ['0'-'9']
 let digits = digit digit*
+let alpha  = ['a'-'z']
+let id     = alpha (digit|alpha)*
 
 let seconds = digits  ('.' digits)?
 
@@ -31,7 +33,8 @@ rule token = parse
 | '('             { LPAREN }
 | ')'             { RPAREN }
 | '^'             { CARET }
-
+| '='             { EQUAL }
+| id as id        { ID(id) }
 | _               { EOL }
 
 | eof             { EOL }

lib/parser.mly

@@ -1,7 +1,22 @@
+
+%{
+
+let fail fmt = Printf.ksprintf failwith fmt
+
+let t = Hashtbl.create 10
+
+let add id num = Hashtbl.replace t id num
+let lookup id = Hashtbl.find_opt t id |> function
+  | Some v -> v
+  | None -> fail "unknown value %s" id
+
+%}
+
 %token <float> NUM
+%token <string> ID
 %token PLUS MINUS TIMES DIV CARET
 %token LPAREN RPAREN
-%token EOL
+%token EQUAL EOL
 %left PLUS MINUS        /* lowest precedence */
 %left TIMES DIV         /* medium precedence */
 %nonassoc UMINUS        /* highest precedence */
@@ -16,6 +31,8 @@ main:
 ;
 expr:
     NUM                     { $1 }
+  | ID                      { lookup $1 }
+  | ID EQUAL expr           { add $1 $3; $3 }
   | LPAREN expr RPAREN      { $2 }
   | expr PLUS expr          { $1 +. $3 }
   | expr MINUS expr         { $1 -. $3 }

tcalc.opam

@@ -1,6 +1,6 @@
 opam-version: "2.0"
 synopsis: "Minimal desktop calculator for timestamps"
-description: """
+description: """\
 TCalc implements a minimal desktop calculator that in addition to
 floating point numbers recognises durations in hh:min:sec format and
 converts them to seconds. This can simplify time-based calculations."""